International Journal of Modern Physics B

Honeycomb composites are now fairly widely used in civilian and military aircraft structures. Common defects found in these materials are delaminations by impact damage and their presence will lead to structural weaknesses which could lead failure of the airframe structures. It is important to develop effective non-destructive testing procedures to identify these defects and increase the safety of aircraft travel. This paper describes the detection technique of impact damage defect using thermography and ESPI. The results obtained with the two techniques are compared with ultrasonic C-scan testing. The investigation shows that both imaging NDT methods are able to identify the presence of artificial defect and impact damage. The adoption of the thermography allowed significant advantages in inspection condition, and gives smaller error in quantitative estimation of defects.

An acoustic wave signal measured on the gas pipe due to impact force is transfer to the far distance through the medium inside of duct. This signal is very complex since it includes the acoustic wave and solid wave. Acoustic wave is affected by the cavity mode inside of duct. The analysis of this acoustic wave gives information about the impact force. For the analysis of this signal, the correlation technique has been used for a long time. This method has a limitation for the application since the waves have dispersive and cavity mode characteristics for the flexible wave. In this paper, we present the time-frequency method for the identification of impact force and the location of impact on the gas pipe. The results give the useful information for the impact force and are applied to the analysis of leakage location of the gas pipe.

A theoretical analysis of the stress state in specimen of the SHPB experiment was performed in consideration of lateral inertia effect. The nonuniformity of lateral stress in specimen and variety of deforming velocity in the loading process were taken into account in the analysis. A formula to correcting the lateral inertia effect was obtained. The force and deformation velocity of specimen-bar interfaces during the loading process got from a numerical simulation of SHPB were used to verify the theoretical analysis formula. It shows that the deviation of reconstructed curve from the inputted relationship can be brought down with the correction formula.

A pendulum-impact testing machine was developed to measure the impact strength of ball-grid-array (BGA) solder joints between an electronic package and a circuit board. Ball solders were connected to daisy-chain between a dummy electronic package and a circuit board. The upper side of the package was directly bonded to a load cell. The rear side of the circuit board was also bonded to an aluminum alloy block fixed on a base. A pendulum made of aluminum alloy was collided into the load cell to apply tensile impact to the solder joints through the load cell. The history of the impact load could be controlled by raising the angle of the pendulum. The fracture of a BGA solder joint was detected by measuring the resistance of the daisy-chain circuit on the board. Therefore, the impact strengths of the solder joints at electrical disconnection and mechanical breaking of all joints could be determined. The experimental results showed that this method is useful for measuring the impact strength of BGA solder joints.

The nose of a missile, flying through raining region with a supersonic speed, is subjected to the rain erosion because the nose is made of a brittle ceramic material. Various test methods are used to address such a phenomenon. However, most of the methods are expensive and/or require complicated facilities. The simple yet very effective rain erosion test method is developed. It consists of (1) a low pressure air gun, (2) a sabot assembly for launching single rain drop, (3) a stopper, and (4) a specimen holder block. The sabot assembly similar to the hypodermic syringe carries specific amount of water toward the stopper launched by the low pressure air gun. When the impact occurs against the stopper which stops the sabot, the water and the steel plunger (at the back of the sabot) continues pushing the sabot to generate a high pressure in the chamber filled with resilient silicon rubber. The pressurized silicon rubber then is squeezed through the small opening in front of the sabot, thus, accelerates the water droplet to a much higher velocity. The velocity of the droplet is measured by the make-screen method, where there are two aluminum foils with an insulating layer in between. The droplet velocity up to 800 m/s is successfully attained using a low pressure air compressor. The specimen made of a ceramic material is placed in front of the high speed water droplet and the rain erosion damage on the surface of the specimen is observed.

A mini-Split Hopkinson Tensile bar (mSHTB) system is developed. The system employs small diameter polymeric bars, which can achieve a closer impedance match with the specimens, thus it provides a lower noise-to-signal ratio and a longer duration of tensile pulse, which results in a higher maximum strain. With the three element viscoelastic model, a characteristic method for reconstruction of the profiles of strain, particle velocity, and stress in an arbitrary cross section of a viscoelastic bar on the basis of the strain signal measured in one section is developed. Experiments using the mSHTB enable us to appropriately characterize the dynamic behavior of small-sized, low-impedance material under a particular range of high strain rate.

In order to evaluate dynamic deformation behaviors under high strain rates, Kobe Steel has developed and applied a Split-Hopkinson Bar (SHB) apparatus. This paper discusses the validity of the strain measurements and strain rates measured by this SHB apparatus. The strain waves that propagated in the incident and transmitted bars and the specimen are captured using a high-resolution type high-speed photography in detail. The strain wave propagated many times in the incident and transmitted bars and the specimen when the specimen was not broken. The amount of the deformation of the specimen decreases with the propagation frequency of the incident wave. On the other hand, to improve accuracy at the strain and strain rate calculated by the one-dimensional stress wave theory, Young's modulus, the longitudinal wave speed, and the density were accurately determined. It was understood that the calculation value showed the strain and strain rate captured with the high-speed photography are a good agreement. As a result, the validity of the measurement accuracy of this SHB could be shown.

Reliability of automotive parts has been one of the most interesting fields in the automotive industry. Especially small DC motor was issued because of the increasing adoption for passengers' safety and convenience. This study was performed to develop the accelerated life test method using Inverse power law model for small DC motors. The failure mode of small DC motor includes brush wear-out. Inverse power law model is applied effectively the electronic components to reduce the testing time and to achieve the accelerating test conditions. Accelerated life testing method was induced to bring on the brush wear-out as increasing voltage of motor. Life distribution of the small DC motor was supposed to follow Weibull distribution and life test time was calculated under the conditions of B₁₀ life and 90% confidence level.

In this paper, Split Hopkinson Bar technique was used to investigate the shear behaviour of adhesively bonded assemblies at high rates of loading. New sample geometry was adopted so that the compressive wave is transformed in a shear loading in the sample. Samples are conditioned at 20°C and 50% of hygrometry to eliminate any interference with temperature and humidity effects. The new technique is applied to an assembly built with a cyanoacrylate based adhesive and a metallic (Steel) adherent. They are found to be highly rate sensitive.

In this paper, three types of projectiles were designed, which are based on the physical mechanism of high-speed penetrating into concrete targets. The three types of projectiles are ogive nose followed by cylinder, cone and grooved cone shank respectively, which are made of 30CrMnSiNi2A with the yield strength 1570MPa. The unconfined compressive strength of concrete target for test is 50MPa. Seven experiments for striking velocities between 800 and 1100m/s were conducted. The experiments showed that the projectiles of cone and grooved cone shank have better penetration performances and the penetration channels were very straight. Compared with the cylinder shank projectiles, the cone and grooved cone shank projectiles are more effective under the condition of high velocity penetrating into complex geological materials as concrete or rock.

In this paper, the influence of plastic deformation on the rebound behaviour of spheres during oblique impacts with a substrate at various impact angles is analysed using Finite Element Methods (FEM). Both oblique impacts of the elastic spheres with an elastic-plastic substrate and those of an elastic-plastic sphere with an elastic substrate are considered. For each impact case, impact angles ranging from 0° to 85° are specified by either keeping the impact speed constant, i.e, changing impact angle will vary both the normal impact velocities and tangential velocities, or keeping the normal impact velocity constant, i.e., only the tangential velocities are changed for different impact angles. It has been found that, during oblique impacts, the plastic deformation not only dissipates the initial impact kinetic energy but also leads to permanent deformation of the impacting bodies that significantly affect the rebound behaviour of the spheres, especially at relatively high impact angles. Consequently, the rebound behaviour of spheres during oblique impacts depends upon which of contacting bodies (the sphere or the substrate) deforms plastically and different rebound behaviours were observed between the impacts of an elastic sphere with an elastic-plastic substrate and those of an elastic-plastic spheres with an elastic substrate.

An experimental investigation is undertaken to examine the possibility of producing ultra-fine grained bulk material through high-speed impact compression followed by annealing. A gas gun was employed to impose high-rate deformation on oxygen-free high-conductivity copper specimens to 90% strain. Samples were also quasi-statically compressed to identical final strains and similar heat treatment. Results show that after impact compression, grain boundaries widen and become less sharply defined, and many narrow twins are formed. For dynamic loading, grain boundary slip appears to accompany dislocation movement. Two dislocation characteristics were identified and the dislocation density was lower than that in samples compressed quasi-statically. Small dislocation loops were also observed. Portions of grains in specimens subjected to impact were mechanically broken into sizes less than 1 μm before annealing. The microhardness of impacted and statically compressed samples increased respectively by HV50 and HV60. After annealing at 190°C for 1 hour, ultra-fine grains with grain sizes ranging from 40∼200 nanometers were observed in impacted samples. This study highlights the potential of utilizing impact compression to produce bulk material with ultra-fine grains.

Steinberg-Guinan constitutive model is widely used in impact engineering simulations. Shock wave profile measurements of Al, Cu, and W under shock pressures ranging from 4 GPa to 200 GPa were analyzed, and shear modulus G and yield strength Y of these materials were obtained by using the high-pressure sonic velocities and rate independent Lagrange analysis results. Then values of derivatives of G and Y with respect to pressure or temperature at the reference state of these three metals were determined. By analyzing the pressure and temperature dependence of shear modulus and yield strength, we conclude that the relations of Steinberg-Guinan constitutive model, Y/G=constant, are approximately correct on Hugoniot state for these materials. So this is a probable approach to solve the difficulty of measurement of Y under high-pressure and high-temperature directly.

The dynamic compressive properties of 96.3Sn3Ag0.7Cu and 99.3Sn0.7Cu solders were studied by means of a split Hopkinson pressure bar at strain rates ranging from 500 to 2000 s⁻¹. Tests were conducted at room temperature and under uniaxial compressive conditions. Eutectic SnPb solders were used as the reference. From the data of tests, it was found that yield strength and flow stress increased remarkably with the increase of strain rate. On logarithmic scales, the yield strength increased linearly with strain rate. These lead-free solders revealed certain visco-plastic behavior and strain rate sensitivity, which predicted using Johnson-Cook material model. Related parameters in the model were determined from the experiment. Compared with the typical Pb-containing solder Sn63Pb37, these lead-free solders showed some fine properties and could substitute some Pb-containing solder alloys in microelectronic components packaging and interconnects.

Effect of alloy composition on impact tensile properties in Al-Mg-Si base alloys was investigated by means of the split Hopkinson pressure bar method. As a result of the impact test, it was proved that the nominal stress for 5% plastic strain was not changed by changing the strain rate regardless of the alloy composition. In the impact test, the elongation was decreased with increasing the amount of excess Si, while that was increased by the addition of Cu. Fractography revealed that the reduction of the elongation in the excess Si alloy was caused by the change of the fracture mode from the mixture of transgranular and intergranular fracture to the intergranular fracture.

The objective is to characterize the effect of the bimodal distribution of rubber particles and its blend ratio on the mechanical properties of the thermoplastic polypropylene blended with two different styrene-ethylene-butadiene-styrene tri-block copolymer (SEBS) at the intermediate and high strain rates. Tensile tests are conducted at the nominal strain rates from 10⁻¹ to 10² (1/sec). Phase morphology is investigated to estimate the bi-modal rubber particle size distribution. In addition, the in-situ observation is conducted during uniaxially stretching within transmission electron microscopy (TEM) step by step to investigate the deformation events depending on the elongation of samples. The elastic modulus increased gradually as the blend ratio of large rubber particle increased. An increase in the rupture strain was found for the bimodal rubber-particle distributed blend system where the blend ratios of small rubber particle and large rubber particle were the same. This is because the smaller particles dominant blend systems show the band-like craze deformation while the localized plastic deformation is taken place in the larger particles dominated blend systems. The synergistic effect of these rubber particles gives rise to a strong increase in the ductility of these bimodal rubber-particle distributed polypropylene systems.

The dynamic stress-strain characteristics of magnesium alloys have not been clarified sufficiently. Thus, the study investigated both the compressive and tensile dynamic stress-strain characteristics of representative magnesium alloys: AZ61A-F, ZK60A-T5 and AZ31B-F at wide strain rate and temperature ranges. About the strain rate dependency, the dynamic stresses are higher than the static ones under both compressive and tensile loads at elevated temperatures; however the dynamic stress-strain relations change slightly in the dynamic strain rate range. Thus, the magnesium alloys has little strain rate dependence. However, the elongation of the dynamic stress-strain relations under tensile load tends to be larger than that of static one. About the temperature dependency, the yield and flow stresses of the investigated magnesium alloys under compressive load decrease abruptly at temperatures higher than about 600 K in the wide strain rate range. Meanwhile, the ones under tensile load decrease with the temperature more gently. Totally, the magnesium alloys exhibit low temperature dependence. Furthermore, as well known, the yield stresses caused under the tensile load exhibit about twice as high as those under compressive load. This study verified that such a characteristic can be observed over a wide strain rate and temperature ranges.

In this research, the effects of pre-fatigue on the dynamic and quasi-static tensile properties of laser welded butt joints between three kinds of steel plates, i.e. HR270, HR590 and HR780 steels, were investigated using tensile split Hopkinson bar apparatus. There were no significant effects of pre-fatigue on the dynamic and static tensile properties of HR780-HR270 and HR780-HR590 joints. Their fracture occurred in the middle of the weaker base metal parts. However, one or two in three pre-fatigued HR780-HR780 joint specimens broke at the heat affected zone, irrespective of strain rate. Their elongation decreased dramatically from that of the virgin specimens, although there are no changes in the tensile strength.

There are at present several applications where high strength ceramics have replaced metals that are subjected to high speed impact from projectiles. This requires an evaluation of behavior of ceramics under impact at high strain rates. This current study provides information on high strain-rate behavior of alumina tested in shear using torsional Hopkinson bar. Dynamic stress-strain curves were generated to investigate deformation behavior prior to fracture while fractography of the broken specimens was carried out to establish the mode of failure. The results of this investigation are similar to what is obtainable in metallic materials in which mechanism of damage is controlled by strain localization and formation of adiabatic shear bands.

Effects of test temperature and alloy composition on dynamic deformation behavior of Zr-based amorphous alloys were investigated in this study. Dynamic compressive tests were conducted in the temperature range from room temperature to 380°C using a compressive Kolsky bar. Dynamic compressive test results indicated that both maximum compressive stress and total strain of the amorphous alloys decreased with increasing test temperature because shear bands could propagate rapidly as the adiabatic heating effect was added at high temperatures. Maximum compressive stress and total strain of the alloy containing ductile β crystalline phases were higher than those of the monolithic amorphous alloys over the tested temperature range because β phases played a role in forming multiple shear bands. The alloys having lower T_g or ductile phases had more excellent dynamic properties than the LM1 alloy.

In this study, dynamic deformation and fracture behavior of ultra-fine-grained dual phase steels fabricated by equal channel angular pressing (ECAP) was compared with that of conventionally annealed ultra-fine-grained steels. In the ECAPed conventionally annealed specimen, pearlites were decomposed, and the ferrite grain size increased up to 0.5 μm. The intercritically annealed specimen consisted of dual phases of equiaxed ferrites and blocky martensites (volume fraction; 35%, size; 1 μm). The dynamic torsional test results indicated that maximum shear stress of the annealed specimens was lower than that of the as-pressed specimen, but fracture shear strain was higher. These results suggested that annealing or promoting dual phase microstructures of the ECAPed specimens could be a good way to increase the fracture resistance under dynamic loading, as it reduced or prevented the formation of adiabatic shear bands or voids. In particular, the ECAPed ultra-fine-grained dual phase steel can be more reliably used under dynamic conditions since it overcomes the shortcomings of reduced strain hardenability, ductility, and dynamic properties.

Impact processes are often analyzed using the coefficient of restitution which represents the kinetic energy loss during impact. In this paper the effect of strain rate dependency of the yield stress on the coefficient of restitution is investigated experimentally and numerically for the impact of a steel sphere against a steel rod. Finite Element simulations using strain-rate dependent material behavior are carried out. In addition, Finite Element simulations with elastic-plastic material behavior, which ignore the strain rate dependency, are carried out as well as elastic material behavior. Comparisons between the experiments and the simulations using strain-rate dependent material behavior show good agreement, and also prove the strong dependency of the coefficient of restitution on the strain rate dependency of the yield stress for steel. The results from both, the experiments and the simulations show also the strong influence of the wave propagation in the rod on the coefficient of restitution.

The high density ferroelectric ceramic with composition near Pb_0.99(Zr_0.95Ti_0.05)_0.98Nb_0.02O₃ (PZT 95/5-2Nb) has been studied under dynamic loading. To characterize its ferroelectric-to-antiferroelectric(FE/AFE) phase transition under shock wave compression, reverse-impact experiments were conducted to determine the Hugoniot states of poled and unpoled PZT 95/5-2Nb, and the shock-induced depoling currents were examined in an external circuit under short-circuit conditions for the poled PZT 95/5-2Nb. The Hugoniot data and current results identify that the phase transition of FE/AFE has occured in the stress range of 0.4 GPa~1.8 GPa. In the phase transition stress range, the measured short-circuit currents show the increasing of rise time and the decreasing of final levels with the increase of shock stress.

The compressive properties of a biodegradable plastic were measured over a wide range of strain rates from 10⁻⁵ to 10⁴s⁻¹, using a universal testing machine and a split Hopkinson pressure bar method. The yield stress of the biodegradable plastic increased with increasing strain rate and decreased with temperature and water absorption. Empirical equations for the yield stresses were derived for the strain rates from 10⁻⁵ to 10³s⁻¹ and from 10³ to 10⁴s⁻¹, respectively.

High-porosity materials, such as chamotte and mullite, possess a heat of fusion. Owing to their properties, these materials can be used with success as damping materials in containers for airplane, automobile, etc. transportation of radioactive or highly toxic materials. Experimental studies of the dynamic properties have been executed with using some original modifications of the Kolsky method. These modified experiments have allowed studying the dynamic compressibility of high-porosity chamotte at deformations up to 80% and amplitudes up to 50 MPa. The equations of the mathematical model describing shock compacting of chamotte as a highly porous, fragile, collapsing material are presented. Deformation of high-porous materials at non-stationary loadings is usually accompanied by fragile destruction of interpore partitions as observed in other porous ceramic materials. Comparison of numerical and experimental results has shown their good conformity.

Results of experimental studies and numerical modeling of high strain rate of aluminum alloy AK4-1 (analog AU2GN) have been presented. Using Split Hopkinson Pressure Bar (SHPB) method stress-strain curves under compression and tension have been obtained. On the basement of these results appropriate parameters of some constitutive equations have been calculated. Strength and deformation material failure properties, dynamic crack resistance, dynamic friction factor for material pair aluminum-titanium have been obtained by carrying out of modificated SHPB tests. A verification of the constitutive equations has been realized by dynamic indentation method and modified Taylor test.

Sandwich panels can be manufactured in many ways like lamination press, closed mold fabrication, and vacuum bag compaction. During manufacturing, the core and the sheets are attached under certain applied pressure and temperature, associated with a deformation and stress remaining in the sandwich core. This study presents an evaluation of the compressive residual stress effect of the core which occurs during the localized shock loading at the mid-span of a clamped sandwich plate. We simulate such a square lattice core sandwich plate by commercial finite element code, ABAQUS/Explicit. We apply uniform distributed loading on upper face sheet and temperature difference occurred during the manufacturing process is taken here before the impact simulation step. These loadings induce certain amount of residual stresses in core structure of sandwich panel. The computational result from non-residual stress case is verified by comparing with the results of published experimental data on similar investigation. In addition, the effect of existing residual stress at core is analyzed. We also compare the dynamic responses of two clamped sandwich plates with and without pre-stressed core. And impact resistance of sandwich panel is explained in the view of energy capacity. Results show that the shock loading behavior of sandwich panel depends on its manufacturing process and panels with compressive residual stresses have less deformation and high impact energy absorption characteristics.

In this study, we analyzed the relation between mechanical and ballistic properties of several engineering ceramics that were expected to be used as armor materials. After the measurements of mechanical properties (Young's modulus, density, hardness, flexural strength and toughness), we measured the ballistic properties against a long rod KE projectile (L/D=10.7, Kinetic Energy, tungsten heavy alloy) and copper jet projectile (40mm shaped charge warhead). The ballistic properties were generally increased as the increasing ratio of mechanical properties and density. As the HEL/density ratio was increased, it especially appeared that the ballistic properties were lineally increased.

To estimate the strain rate dependence of the dynamic flow stress of aluminum alloys, 2017-O and - T4, high strain rate and rate reduction tests are performed at strain rates ranging from about 1000/sec to 30000/sec. A steep increase in the flow stress is observed for 2017-O at the strain rate of about 3000/sec. For 2017-T4, the above phenomenon is observed at the strain rate above about 10000/sec. A simplified model for dislocation kinetics under dynamic plastic deformation is employed which can represent a transition in the rate controlling mechanism of dislocation motion from a thermally activated process to a viscous drag. It is expected that the steep increase in the flow stress observed at high strain rates is attributed to the rate dependence of the viscous drag on the dislocation motion.

Impact stress wave propagating through porous materials is investigated in order to examine the ability of the shock absorbing effect. The specimens are modeled as the porous medium with different porous diameters made of the acrylic resin plate. When these models are impacted with different impact velocities, the impact stress waves propagating before and after the porous parts are measured using the strain gages in the experiments. As the reduction effect of the impact stress wave propagating in the porous medium, we pay attention to the maximum stresses and the duration times from the histories of the impact stress waves. One-dimensional wave theory and dynamic element method simulated this model are applied in order to explain these phenomena.

The effects of microstructures of Ti-6Al-4V alloy on the flow stresses and fracture behaviors at quasi-static and dynamic deformation conditions were investigated. Specimens of different sizes and fractions of α globules in equiaxed and bimodal structures were compressed at the strain rate of 2×10⁻³/s and 3×10³/s using hydraulic testing machine and split Hopkinson pressure bar, respectively. The a globule size in equiaxed structure changed the level of flow stresses, but did not affect the strain hardening characteristics. Meanwhile, the volume fraction of α globule (or lamellar phase) in bimodal structures influenced both the flow stress and strain hardening exponent at quasi-static and dynamic deformation conditions. Bimodal structure of 50% lamellar fraction is considered to be more favorable in dynamic deformation condition at strain rate regime of 3×10³/s than equiaxed or bimodal one having higher lamellar fraction.

A spacer grid assembly is one of the main structural components of the nuclear fuel assembly for a Pressurized light Water Reactor (PWR). The spacer grid assembly supports and aligns the fuel rods, guides the fuel assemblies past each other during a handling and, if needed, sustains lateral seismic loads. The ability of a spacer grid assembly to resist these lateral loads is usually characterized in terms of its dynamic and static crush strengths, which are acquired from tests. In this study, a finite element analysis on the dynamic crush strength of spacer grid assembly specimens is carried out. Comparisons show that the analysis results are in good agreement with the test results to within about a 30 % difference range. Therefore, we could predict the crush strength of a spacer grid assembly in advance, before performing a dynamic crush test. And also a parametric study on the crush strength of a spacer grid assembly is carried out by adjusting the weld penetration depth for a sub-sized spacer grid, which also shows a good agreement between the test and analysis results.

The deformation of polymers under high loading-rate conditions will be a governing factor to be considered in their impact-resistant applications such as protective shields and armors. In this study, the deformation and fracture behaviors of polymeric materials such as PE, PC and PEEK have been investigated by Taylor cylinder impact tests with the high speed photography. A 20 mm air gun was used to perform the impact experiments. Cylindrical projectiles have been impacted onto a hardened steel anvil at a velocity ranging from 120 to 320 m/s. After impact experiments, the shape of projectiles was examined and compared with high speed photographic images to distinguish the elastic deformation component from the deformation measured instantaneously. Each adopted material showed different deformation and fracture behaviors. As compared with the quasi-static cases all polymers showed a significant strain rate hardening when the strain rate used was over 6 × 10³s⁻¹. This appeared most significant in PE.

This paper is concerned with modified integration algorithm in the strain space for rate and temperature dependent elasto-plastic constitutive relations in order to obtain more accurate results in numerical implementation. The proposed algorithm adopts both the 2-stage Lobatto IIIA with second-order accuracy and the iteration procedure using the Newton–Raphson method to enfoce consistency at the end of the step. The algorithm enables to consider the convective stress rates on the yield surface in the strain space in the numerical integration of the constitutive model. Accuracy assessment using the isoerror maps and FEM analysis of the adiabatic shear band is carried out in order to demonstrate the accuracy of the proposed algorithm.

The sensitivity of the flow stress of polymers to strain-rate is one of the major concerns in mechanics of materials since polymers and polymer matrix composites are widely used in many engineering applications. In this paper, we present tests on Nylon 6 and Nylon 66 on wide range of strain-rates (0.001-5000s⁻¹). Specifically, we used INSTRON machine for low strain-rates. The high strain-rate measurements were inferred from the Hopkinson bar tests. Only the compressive behaviour was investigated. To eliminate any interference with temperature and humidity effects, test samples were conditioned at 20°C and 50% of hygrometry. Moreover, the effects of the specimen geometry were considered. The current study results are also compared to values found in literature.

The tensile stress-strain curves of iron and a variety of steels, covering a wide range of strength level, over a wide strain rate range on the order of 10⁻³ ~ 10³s⁻¹, were obtained systematically by using the Sensing Block Type High Speed Material Testing System (SBTS, Saginomiya). Through intensive analysis of these results, the strain rate sensitivity of the flow stress for the large strain region, including the viscous term at high strain rates, the true fracture strength and the true fracture strain were cleared for the material group of the ferrous metals. These systematical data may be useful to develop a practical constitutive model for computer codes, including a fracture criterion for simulations of the dynamic behavior in crash worthiness studies and of work-pieces subjected to dynamic plastic working for a wide strain rate range.

The aim of this study is to fabricate a high volume fraction B₄C-reinforced intermetallic matrix composite by the dipping exothermic reaction process and investigate the shock impact damage response of composites by explosive indentation experiment. It has been shown that the final microstructure of the dipping exothermic reaction process-fabricated composite can be tailored by treatment of the constituent powders and post heat treatment. The hardness and impact damage resistance of the fabricated composites were evaluated.

Historical review of research and development of the SHPB method in Japan is outlined. After introduction of the SHPB in early 1960s, various kinds of compression, tension, torsion and bending tests have been performed in Japan and are presently shown together with special techniques such as the strain rate change test and the ramped wave method. Applications of the SHPB method to characterize dynamic response of materials from various points of view are also described in connection with its flexibility and simplicity. Current activities related to the SHPB method are briefly explained.

The important mechanisms for defeating armor piercing (AP) projectiles are reviewed in this paper. These mechanisms are based on the compressive strength of the target material (its inherent resistance to penetration) and on the asymmetrical forces which it exerts on the threat, through proper geometrical arrangements. We discuss the basic features of the resistance to penetration, starting with the classical analysis of the cavity expansion process in elasto-plastic solids. This property of the target is responsible for the deceleration of hard cored projectiles and for the erosion of long rods, under normal impact conditions. We then discuss the asymmetrical interaction of AP projectiles with inclined plates (metals and polymers) and with ceramic spheres. These asymmetric forces are responsible for their deflection and breakup. Our work combines experimental observations with numerical simulations and engineering models, which enhance the understanding of the various phenomena encountered in these complex situations. This understanding is necessary for optimizing the performance of any armor design against a given threat.

The interaction of the flying plate with the Long-rod penetrator has been studied both experimentally and numerically using the LS DYNA 3D finite element code. The influence of the plate velocity and plate material on this interaction has been investigated in details. Numerical results show that there was a relatively large damage of the projectiles. The extent of this damage well agree with our experimental foundings. The numerical simulation of the damaged projectiles with some targets has been also performed

The RHT concrete strength model and failure model are employed for the numerical simulations of composite projectile penetrating concrete targets. The simulations show that RHT parameters, specially the failure parameters, greatly influence the penetration depth, exit velocity. The failure mode of concrete should be paid great attentions in numerical analysis. If the crushing failure is the primary mechanism, RHT model seems effective. For the cracking process of concrete, the model should be tensile failure description. Reasonable material parameters are important in penetration simulations. Comparison between numerical analysis and experimental date is made for discussion about the parameter effects.

In this paper, the oblique penetration and perforation process has been analyzed in three stages.

In the first and second stages, the entering of projectile nose into the target and the tunneling process have been considered, respectively. The calculation of force in these stages is based on spherical cavity expansion method. In both of these stages, the friction coefficient has been considered to vary with velocity changes during the process. At the end of each time step, the velocity components are readily determined by solving the equations of motion. The plug formation is modeled in the third stage, where the residual velocity is calculated by the application of energy balance.

In summary, a new approach has been developed to determine the residual velocity, the exit angle, and the depth of penetration of projectiles with spherical nose into the targets, for both cases of oblique and normal striking. The predicted results from this analytical model are in good agreement with experimental and analytical results from other researchers.

We have experimentally investigated the influence of fluoroplastic, copper, and silicon carbide inert inserts on the process of detonation transmission through water. Active and passive HE charges were molded from high explosive (HE) Comp. B. The diameter and height of HE cartridges were 40 and 40 mm, respectively. On the rear end of the passive HE charge a steel witness plate was mounted, which detected presence or absence of detonation. Inert inserts were shaped as 20 mm × 20 mm square prisms of varying lengths, and were contained between active and passive HE charges without any clearance on the way of initiating shock wave with partial overlap of HE cross sections. We demonstrate that preloading a passive HE charge with a shock wave transmitted through a copper or a ceramic insert causes considerable desensitization of the Comp. B. Other conditions being the same, the crash distance of detonation transmission for copper was equal to 74%, and for silicon carbide – to 60% of the distance for fluoroplastic. This desensitization phenomenon may be used for development of protective shells for HE. While performing experiments with 20 mm ceramic inserts we have observed unknown cumulation phenomenon, which manifested itself as a hole in identification steel specimen with depth of about 10 mm.

The response of the side shell to non-contact underwater explosion is of major concern in ship design. While extensive research is carried out on air-backed plates, relatively less attention is paid to water-backed plates. Nevertheless, the response of the water-backed plates becomes relevant when the water filled side shells are exposed to an underwater shock loading. Availability of scant information on the experimental results of water-backed plates is the primary motivating factor to make analytical estimates. These estimates are provided in comparison with an air-backed plate for identical attack geometry and target parameters. This work aims to bring out a comparative procedure for the damage assessment between air- and water-backed plates so that the response of the latter can be presented in terms of that of the former.

To obtain a better understanding of detonation properties of ammonium nitrate (AN) and activated carbon (AC) mixtures, steel tube tests with several diameters were carried out for various compositions of powdered AN and AC mixtures and the influence of the charge diameter on the detonation velocity was investigated. The results showed that the detonation velocity increased with the increase of the charge diameter. The experimentally observed values were far below the theoretically predicted values made by the thermodynamic CHEETAH code and they showed so-called non-ideal detonation. The extrapolated detonation velocity of stoichiometric composition to the infinite diameter showed a good agreement with the theoretical value.

The terrorist explosion is dreadful for current world. In various explosive events, vehicle bomb explosion has been commonly used by terrorists to approach the targets. This paper evaluated and analyzed the minatory grades of various vehicle bombs, and calculated the failure distances of the buildings under the main impulse effect of air shock wave. Thereafter, a few kinds of setting methods of the blast resistant walls under various vehicle bombs are established. The research will provide effect protective measures for the survival ability of the important buildings under various vehicle bombs.

In a nuclear power plant, impact force due to loose part is related to the structural damage in the plant. In general, the steam generator of the nuclear power plant is structured by thick plate. The paper presents a novel approach to locate an impact load in a thick plate. The approach is based on the analysis of the acoustic waveforms measured by a sensor array located on the plate surface. For accurate estimation of the location of the impact source, the time differences in the arrival times of the waves at the sensors and their propagation velocities are determined. The dispersion curves for multi modes of Lamb wave are calculated by using exact plate theory and SDPT. It is difficult to measure directly the group velocity for Lamb mode of acoustic waveform in the thick plate because they are dispersive wave. However, most of the energy in the wave is carried by the flexural waves (A0 mode), the group velocity of this mode is extracted using the CHOTF technique for estimating the impact source location. The estimates are shown to be in excellent agreement with the actual locations and it is applied to the damage analysis due to the loose part in a nuclear power plant.

To investigate the structural response of sandwich panels loaded by impulsive loads, a systematic investigation has been conducted, and some experimental results are reported and discussed in this paper. Quantitative results were obtained based on the measurement in the tests by a pendulum with corresponding sensors, and then the deformation/failure patterns of front face and core were classified and analyzed systematically. Finally, an empirical equation is proposed to predict the back face deflection of the panels.

The in-plane impact behaviors of honeycomb structures with some cells randomly filled with stiff inclusions were analyzed by using the finite element method (FEM). The effect of the random arrangement of inclusions on the deformation processes of the honeycomb structures was considered. During these deformation processes, the growth of shear bands was disturbed by the inclusions and the cell region surrounded by inclusions did not deform. The average stress increased and densification strain decreased with increasing volume fraction of inclusions. A honeycomb with volume fraction of inclusions of 0.5 could not be deformed. Below 0.5, the average stress steeply increased and densification strain approached zero. Some models for less than a volume fraction of inclusions of 0.25 had higher absorbed energy than the model with no inclusions and others had lower energy. Above 0.25, the absorbed energy decreased and linearly reached zero at a volume fraction of inclusions of 0.5.

In this paper, a solution method for the response of a thin shell structure subjected to low velocity impact by a sphere is presented. The governing equation of the impact process is obtained by simultaneously solving the equations of motions for the sphere and shell. The derivation is based on the explicit expression of the displacement of the mid-surface of the shell under a single impulse load acting normal to apex of the shell. Incorporating the theory of convolution and Hertz contact law, a non-linear integro-differential equation in terms of the indentation of the contact, for the impact process is derived. The non-linear integro-differential equation is solved by the numerical scheme of Runge-Kutta method to obtain the time history of the contact force at the impact point of the shell. The contact force is then applied on the apex of the shell, the dynamic responses of the shell including the displacement and stress are obtained by the finite element method. The results are validated with the experimental test and numerical calculation published in the literatures. The effects of the radius and velocity of the impactor on the impact response is investigated through parametric study.

Steel plates subjected to low velocity impact were numerically analyzed, and physically tested. The impactor has hemispheric tip nose, and the square plate has four fixed edges. Mindlin plate theory and Hertz contact law were used for the formulation of the impact problem, and some numerical treatments for the reduced integration, Newmark time integration scheme, associative flow rule, and plastic hardening were appropriately applied. A simple and efficient analysis program for plate impact was generated, and the results were compared with those of physical impact experiments. A drop test system was installed, and the impact behavior was measured with sensors. The comparison showed reasonable results, and the main parameters of plate impact were also analyzed.

The impact test on short concrete filled steel tubular column was conducted through DHR-9401 dropped hammer tester. Based on analysis on recorded time-history curve of impact force, the relations of impact force with respect to confining effect coefficient and impact speed are obtained. So are done that of the impact duration. By use of ANSYS/LS-DYNA, values of impact peak force in relation with those of impact speed were computed in the case of unitary material model and composite material model respectively. The simulation results show that peak force-speed curve of unitary model has better description of test data than that of composite one. Critical energy is found to increase linearly with the steel ratio when steel tube and concrete remain unchanged.

To study structure resistance to impact loads using thin-wall cylinder units, knowledge of energy absorption parameters of these test units is required, as well as evaluations of resistance force. Buckling of cylinder test units involves formation of both axisymmetric and non-axisymmetric folds. Repeatability of buckling patterns is an important parameter of the fold formation process and, eventually, of the absorbed energy magnitude. This paper discusses buckling patterns obtained for cylinder test units of three dimension types with scales relating as 1:2:10. The units were made of three materials (steel 09G2C and two aluminum alloys, AMg6 and AMcM) and subjected to static and impact loading. For static loading, a test unit was fixed on a long measuring rod and subjected to an impact by a projectile moving at a speed of V0. The experiments were performed at three loading speeds V₀ 10m/s, 50 m/s, 100 m/s. No less than 5-10 tests were performed for each type of test units, i.e. for each size, material and load level, to study buckling repeatability. Impact velocity and axial compression force history were recorded in the tests. It was obtained in the testing of cylinder test units that: Repeatability of buckling patterns was observed only in the formation of the first fold, which is axisymmetric. Then buckling, in most cases, follows a non-axisymmetric path; -With test unit scale (i.e. size) increasing, its relative energy absorption capacity under impact loading (in ratio to the test unit mass) increases; - There is clear evidence that strain rate influences the material strength properties, except for the aluminum alloy AMg6, whose strength properties depend rather weakly on strain rate. These experimental findings can be used as a benchmark for verification of computer codes, as well as to study the behaviors of cylinder test units subjected to axial impact, which involve both axisymmetric and non-axisymmetric buckling shapes.

The classic plate theory (CPT) as a theoretical solution to an impact load has been used in a thin plate. However, The CPT is not any more useful solution for the impact load in the industrial power plant, which is generally constructed by the thick plate. In this paper a novel and effective approach is developed to determine the time history of the impact load on a thick aluminum plate based on the analysis of the acoustic waveforms measured by a sensor array located on the thick plate surface in combination with the theoretical Green's function for the plate. The Green's functions are derived based on either the exact elastodynamic or theory the approximate shear deformation plate theory (SDPT). If the displacement is measured on the plate, then the time history of impact load can be calculated by deconvolving the measured displacement with the theoretical Green's function. The reconstructed time history for impact load is compared with the time history of the impact load measured by the force transducer. A good prediction is found. This technique presents a valuable method for identification of source and may be applied to in-service structures under impact to signals recorded from acoustic emission of propagating cracks.

In this paper, a virtual testing model (VTM) for the Korean high speed train (KHST) is developed to meet several design purposes, and an improved collision safety assessment method is also suggested. Although twisting, buckling, zigzagging, chain reactions, overriding and derailment have long been recognized as the important elements that can affect the safety of passengers in the event of a collision, the means by which such behaviors can be predicted have been restricted. To address this, a VTM, supported by the technological advancements of numerical analysis software and high-performance computers, was developed to simulate and evaluate such behaviors. The VTM for KHST was modeled using finite elements, in order to obtain such collision behaviors. In addition, the VTM was simulated in a variety of accident scenarios, and the results were analyzed and compared with the results obtained using other modeling techniques. Since factors such as the deformation of individual members, serial collisions and twisting of the train body were incorporated into the VTM, this simulation provides more practical collision responses than other modeling techniques. This shows that it can predict more nonlinear collision behaviors, giving it a wider range of applications.

As the areal recording density increases in hard disk drives (HDDs), the flying physical spacing between the head and the disk decreases and the likelihood of head-disk contact during full speed rotation increases. Therefore, the simulation and modeling of the air bearing slider with ultra-low flying heights becomes an important issue for the operational shock simulation. The static/dynamic properties, including the influence of the radial position and the skew angle of the slider, the rotating speed of the disk, and the shock simulation, of the air bearing slider were analyzed. Generally speaking, for a given rotating speed of the disk, as the slider moves from the inner diameter to the outer diameter, the maximum contact pressure, the skew angle, the pitch angle, and the maximum air bearing pressure increase; while the flying height decreases. These trends are strengthened by a faster rotating speed of the disk. There are obvious oscillations in the air bearing force and the minimum spacing when contact occurs during a shock.

In this study we analyzed the deformation of the polymeric rod impacting on the rigid wall which is called "Taylor impact test."" We simulated three-dimensional Taylor impact test depending on the various polymeric materials using the explicit finite element method by employing DYNA3D code. In simulation, polymeric materials were modeled using viscoelastic constitutive relations with the relaxation time and shear modulus. We have carried out the numerical simulation for the transient deformation characteristics and discussed effects of the viscoelastic constants on the deformation of the polymeric rod under impact.

In this study, nonlinear crash analyses have been conducted for the skid landing gear of helicopter. The realistic configuration of skid landing gear system is considered. Detailed three-dimensional finite element model with variable thickness and material nonlinearity is constructed for required impact design conditions. Advanced computational approach is used to conduct nonlinear transient impact dynamic analyses for different collision models. Characteristics of impact dynamic responses due to the ground crash are practically investigated in detail. It is also shown that the exact consideration of friction effect is very important to accurately predict the crash behavior of the skid type landing gear system. Finally, two typical landing conditions are analyzed and correlated with drop test results.

The dynamic damage evolution for PP/PA blends with different compatibilizers is studied in high strain rates from two different approaches, namely by determining the unloading elastic modulus of specimen experienced impact deformation and by combining the split Hopkinson pressure bar (SHPB) experimental technique with the back-propagation (BP) neural network. The results obtained by both approaches consistently show that a threshold strain ε_th exists for dynamic damage evolution, and both the damage evolution and ε_th are dependent on strain and strain rate. For non-linear visco-elastic materials, the damage evolution determined by the unloading elastic modulus provides an underestimation of real damage evolution.

To participate in Student Formula Society of Automotive Engineers (SAE) competitions, it is necessary to build an impact attenuator that would give an average deceleration not to exceed 20g when it runs into a rigid wall. Students can use numerical simulations or experimental test data to show that their car satisfies this safety requirement. A student group to study formula cars at the Korea University of Technology and Education has designed a vehicle to take part in a SAE competition, and a honeycomb structure was adopted as the impact attenuator. In this paper, finite element calculations were carried out to investigate the dynamic behavior of the honeycomb attenuator. Deceleration and deformation behaviors were studied. Effect of the yield strength was checked by comparing the numerical results. ABAQUS/Explicit finite element code was used.

In this paper, the strain rate effect of energy absorption members in rolling stock is studied using the virtual testing model (VTM) for Korean high speed train (KHST). The VTM of KHST was simulated for two different strain rate conditions. The VTM is composed of FE models for structures, and nonlinear spring/damper models for dynamic components. To simplify numerical model for the full rake KHST, the first three units consist of full flexible multi-body dynamic models, and the remainder does 1-D spring/damper/mass models. To evaluate the strain rate effect of KHST, the crash simulation was performed under the accident scenario for a collision with a rigid mass of 15 tons at 110kph. The numerical results show that the overall crash response of the train is not largely affected as much as expected, but individual components have some different deformations according to strain rate. The deformation of the front end structure without strain rate effect is larger than that with it. However, the deformation of the rear end structure without strain rate effect is smaller than that with it. Finally, the intrusion of the driver's cabin is overestimated for no strain rate effect when compared to the case with it.

Power series method is used to analyze the distribution of stresses of the transversely isotropic cylinder under arbitrary axisymmetrical normal load. The stress function and normal load are expanded as the form of Fourier series. Unknown parameters in equations are determined using boundary conditions and final solutions of stress and displacement are obtained accordingly. The analysis of stresses obtained from different material parameters shows that the axial stress is significantly affected by Young's modulus and the circumference stress is sensitive to the variation of Poisson's ratio.

It is very important to know how the reservoir rock and its fluid properties are linked to seismic dynamic response. Literatures show that there are a variety of rock-physics models such as the most famous Biot-Gassmann equation aimed at the relationship between seismic velocity and liquid saturation. Most of these models make a fundamental assumption of one fluid phase or homogeneous phase within the pore volume. In this paper, we discuss possible seismic velocities change in a two immiscible pore fluids (i.e. water-gas) saturated reservoir with patchy saturation distribution. It is found that P-wave velocity of a reservoir rock with the same saturation but different pore fluid distribution exhibits noticeable variation and deviate overall from Gassmann's results. We use DEM theory to explain this phenomenon. It belongs to hybrid approach in rock-physics modeling and can handle complex pore-fluid-distribution cases. Based on the modeling study, we found that various fluid-distribution models may significantly affect the modulus and P-wave velocity. The seismic reflection time, amplitude and phase characteristics may change with the choice of pore-fluid-distribution models. Relevant rock mechanical experiments indicate the same trend of seismic responses. It also be proven by seismic reservoir monitoring experiment (time lapse study) that incorrect conclusion may be drawn about the strong seismic reflection in pure Utsira Sand if the microscopic pore-fluid-distribution effects are not taken into account.

To understand the dynamic response of transversely isotropic material under explosion load, the analysis is done with the help of ABAQUS software and the constitutive equations of transversely isotropic material with different angle of isotropic section. The result is given: when the angle of isotropic section is settled, the velocity and acceleration of measure points decrease with the increasing distance from the explosion borehole. The velocity and acceleration in the loading direction are larger than those in the normal direction of the loading direction and their attenuation are much faster. When the angle of isotropic section is variable, the evolution curves of peak velocity and peak acceleration in the loading direction with the increasing angles are notching parabolic curves. They get their minimum values when the angle is equal to 45 degree. But the evolution curves of peak velocity and peak acceleration in the normal direction of the loading direction with the increasing angles are overhead parabolic curves. They get their maximum values when the angle is equal to 45 degree.

In this study, theoretical super screen vibration analysis has been carried out to predict the dynamic characteristics of interactive waste particles. The vibrating screen is modeled of three assemblies such as screen, wastes guide, and supported screen. Then materials (or particles) of different size is to be separated by using the eccentric vibrator and classifying tilt plates. In processing separation mechanism, much lighter construction wastes (wood, Styrofoam, etc) and heavier materials are separated by staying time delay in a super screen. The design results, separation screen were able to know that small and larger particles are conspicuous difference each motion character according to trajectory particles, and small particles raise the probability in classifying tilt plates.

When a robot system collides with environment, not only the contact point but also the joints of the robot system experience impulsive forces or moments. In the real environment, the structure collides with environment at multiple points. However, most previous modeling methods have assumed one point contact to environment. In this work, we propose external and internal impulse models in case of multiple contact. The case of one point contact is compared to the case of multiple points contact through simulation.

Predicting microcracking properties of the composite laminates in nonuniform stress conditions was the subject in this paper. The uniform stress field meant the stresses were independent of the width direction. The material was the 954-2A/IM7 laminates containing a central hole. Microcracks initiated at the edge of the hole and propagated into the laminate. Because the tensile stress concentration decreased with distance, the microcracks were arrested before the edge of the laminate. Because carbon fiber composites were opaque, a x-ray method was used to detect the length of the propagating microcracks. The microcracking at the near edge of the hole could be reasonably predicted by considering the local laminate stresses and the microcracking toughness measured in unnotched laminates. However, the data away from the hole did not agree with the predictions. The local microcrack density was always much higher than that predicted by the local laminate stress.

This paper is concerned with the evaluation of the dynamic failure load of the spot weld under combined axial and shear loading conditions. The testing fixture are designed to impose the combined axial and shear load on the spot weld. Using the proposed testing fixtures and specimens, quasi-static and dynamic failure tests of the spot weld are conducted with seven different combined loading conditions. The failure load and failure behavior of the spot weld are investigated with different loading conditions. Dynamic effects on the failure load of the spot weld, which is critical for structural crashworthiness, are also examined based on the experimental data. In order to evaluate the effect of the strain rate on the failure contour of the spot weld under combined axial and shear loads, the failure loads measured from the experiment are decomposed into the two components along the axial and shear directions. Experimental results indicate that the failure contour is expanded with increasing strain rates according to the rate sensitivity of the ultimate stress for welded material.

In order to study the protection behavior of brittle materials against a shaped charge jet, the jet penetration and the fracture behavior have been investigated by the series of photographs taken by the IMACON high speed camera. The examined materials were glass, fused silica, and single crystalline quartz. The trend of crack growth in BK7 glass and fused silica indicated conical shape. In the case of the single crystalline quartz, it was observed that the crack grows fast along the axis of crystal growth. The velocity of shock wave (~ 6km/sec) into glass and fused silica was faster than the sonic velocity. However, the velocity of shock wave in the single crystalline quartz showed to be similar to its sonic velocity. The ballistic protection capability of single crystalline quartz showing fast crack growth has been evaluated to be lower than that of fused silica which has relatively slow crack growth, although the quartz has higher physical and mechanical properties.

The dome port cover of a ramjet engine is used to seal off the ram air inlet during booster operation. When the ramjet engine undergoes the transition leading to ramjet operation phase, the port cover is fragmented by the ram pressure. Lately, the dome port cover has been made using a MACOR glass-filled ceramic that has high heat resistance and high compression strength, as well as low density. In this study, fracture simulations of a ceramic dome under shock pressure were performed through the finite element method, using the nonlinear code LS-DYNA. The material properties of the simulations were applied to the experimental results of a tensile test for the MACOR glass-filled ceramic. The simulation was carried out on the spherical dome model using various impact pulses. The fracture strength and fracture behavior mode were compared for each case. The type-A spherical dome fractured earlier than the other kinds of domes.

Two kinds of theory for non-destructive inspection of ceramics were reviewed, which were derived by the authors using flaw-size distribution. In the sufficient condition theory (Realistic NDI), we had discussed about the screening flaw-size and a screening region. In the necessary and sufficient condition theory (Ideal NDI), we found that the screening flaw-size should be changed depending on stress state and specimen configuration. It was proved that there is one-to-one correspondence between Ideal NDI and a proof test. Applications to machining damage problems and surface strengthening of ceramics were also presented.

The toughness data obtained from Charpy impact tests are presented by a temperature-energy relationship. Data fitting for quantitative evaluation of the transition temperature, upper shelf energy and ductile-brittle transition, in other words, the representation with general mathematical model equation for energy variation according to the temperature is necessary. In this study, the Charpy impact tests to two representative steels were carried out as a research work for the material property standardization technique development. The fitting procedure of the scattering in data according to materials and temperature in the transition region was described. The data fitting procedure using the tangent hyperbolic function was established through variances treatment in the transition region.

In this study, explosive indentations were used to characterize the dynamic damage behavior of silicon nitride ceramics with different microstructures. Three grades of silicon nitrides with different grain size and shape were prepared. Subsurface damage of specimens was characterized extensively using optical and electron microscopy. It was found that the dynamic damage response depends strongly on the microstructure of specimens, particularly on the glassy grain boundary phase.

In this paper, experimental investigation and theoretical analysis are carried out in an attempt to study the response of SiC ceramic matrix composite reinforced with three dimensional braided fabric(3D C/SiC) under high velocity impact. The results show that 3D C/SiC composite will be turned into comminution if the pressure of the impact point resulted from the projectile impacting 3D C/SiC composite sample is larger than 780Mpa. Based on the analysis of the mechanism of composite comminution, a theoretical model has been developed.

The theory studies have showed that, rock burst is a kind of dynamic phenomenon of rock mass in mining, and is a kind of dynamic disaster from mining. The time series of magnitude is a very important exterior behavior of rock burst. The previous studies show that, to model this complicated non-linear time series, the neural network is a very good method. To overcome the shortcomings of traditional neural network, a new kind of evolutionary neural network based on immunized evolutionary programming proposed by author is proposed here. At last, the proposed evolutionary neural network model is verified by a real magnitude series of rock burst. And the result is compared with other method, such as grey system method. The results have showed that, evolutionary neural network model not only has high approaching precision, but also has high predicting precision, and is a good method to construct the non-linear model of rock burst. And this method can be used in a large number of engineering examples.

Airframe survivability and hydrodynamic ram effect of aircraft are investigated. Penetration and internal detonation of a simple tank and ICW(Intermediate Complexity Wing) are simulated by nonlinear explicit calculation. Structural rupture and fluid burst are analytically realized using general coupling of FSI(Fluid-Structure Interaction) and adaptive master-slave contact. Besides, multi-material Eulerian solver and porosity algorithm are employed to model explosive inside fuel and tank bays which are defined in multi-coupling surfaces. Structure and fluid results are animated on the same viewport for enhanced visualization.

Quasi-static contact behavior of an inflated MAXXIS VICTRA MA-Z1 (235/45/R17) radial tire is reported in this work. Compressional response of the inflated tire with a prescribed weight loaded quasi-statically was examined. Both experimental and numerical results were obtained and compared. In addition, dynamic contact simulation of the tire rolling on a dry-flat roadway was also studied. A commercial finite element commercial Code (LS-DYNA) was used to construct the complex tire model and to perform both quasi-static contact and dynamic rolling simulations. The Mooney-Rivlin constitutive relationship was adopted to describe the non-linear elastic behavior of rubber material, and the classical laminated theory was used to model the stress-strain behavior of the fiber reinforced composite layers of tire. Quasi-static contact force and compression displacement of tire were measured and numerically simulated. Contact pressure distribution of the tire tread in touch with simulated rigid dry-flat road surface was also numerically and experimentally obtained. Good relationship between the test findings and simulated results were reported. In addition, the dynamic contact simulations of the inflated tire rolling on a dry-flat rigid roadway with a prescribed weight loaded are presented, and the deformation pattern and local contact stress distribution are also reported.

To predict the behavior of a dual plate composed of 5052-aluminum and 1002-cold rolled steel under ballistic impact, numerical and experimental approaches are attempted. For the accurate numerical simulation of the impact phenomena, the appropriate selection of the key parameter values based on numerical or experimental tests are critical. This study is focused on not only the optimization technique using the numerical simulation but also numerical and experimental procedures to obtain the required parameter values in the simulation. The Johnson-Cook model is used to simulate the mechanical behaviors, and the simplified experimental and the numerical approaches are performed to obtain the material properties of the model. The element erosion scheme for the robust simulation of the ballistic impact problem is applied by adjusting the element erosion criteria of each material based on numerical and experimental results. The adequate mesh size and the aspect ratio are chosen based on parametric studies. Plastic energy is suggested as a response representing the strength of the plate for the optimization under dynamic loading. Optimized thickness of the dual plate is obtained to resist the ballistic impact without penetration as well as to minimize the total weight.

Structure bodies and surrounding soils in certain types of bridges and tunnels may be prone to collisions during earthquake. A dynamic system composed of discrete and finite elements is developed using explicit formulation for equations of motion, and nonlinearities in soils and at interfaces of disjoined regions are implemented. Time history solutions are carried out to examine the plastic deformation in soils as well as the integrity of structures. Two case studies are presented in which collisions among disjoined regions are anticipated in the event of extremely large earthquakes. Case one is based on a replica from a quake-stricken bridge, to illustrate that a backfill with moderate soil strength may be used as an energy-dissipating buffer to contain the shaken loose decks. The other case involves an underground subway station box with slurry walls alongside, to exemplify the seismic resistance of the dual-wall system.

It is quite meaningful in an engineering aspect to investigate liquid drop behaviors in two-phase flow, on which dispersive mixing or overall rheological characteristics heavily depend. There are two approaches numerically to deal with two-phase flow problems, which are the moving- and the fixed-grid methods: that is, interface tracking and interface capturing methods. In this study, we developed multiphase flow codes in both Lagrangian and Eulerian frameworks and compared each solution for the single drop problem in an axisymmetric channel flow. Deformation patterns of drops were observed by these two methods and we have discussed the characteristic features of two methods from the deformation of drop for the moving boundary problems.

Obtaining the more exact parameters of slip surfaces is proved to be crucial in the analysis of landslide stability, and there are four study methods available i.e. in-site test, laboratory test, back analysis and theoretical analysis. In general, the former two are the basic one, whereas the latter two are secondary. A set of test values about shearing stress and direct stress can be obtained through in-situ and lab tests, then the parameters of slip surface should be calculated to fitting for the test value by the least square method usually, but the effect of anomalous values should increase markedly because the quadratic sum of residual errors is adopted in calculations. In order to reduce the effect of anomalous value, a new method based on the robust regression analysis and the particle swarm optimization method are adopted to calculate the mechanics parameter of landslides in this paper. In the new method, the sum of residual absolute values is used to replace the quadratic sum of residual error, and then the quadratic sum of anomalous value can be avoided. Comparing to the least square method, the new method can reduce availably the effect of abnormal values, and the results are more credible. Furthermore, an engineering example is cited to show the validity.

The total stress in a structure changes dynamically by the stress multiplication phenomenon in the case of a fixed boundary condition. Therefore, it is important to evaluate the reflected stress waves under an impact loading in structures. In many problems, the method of the classical position-time diagram of wave fronts is effective to analyze the maximum stress in the structure under the impact loading and for a simple arrangement of members along the axis of the one-dimensional structure. In this study, stress analyses in one-dimensional structures based on the position-time diagram of stress wave fronts were realized as a computational method with and without attenuation of stress wave. This method was applied to the problem of stress analyses in a bone under an impact loading, and the stress states were compared with the experimental results.

In Korea, it has been planned to apply high speed tilting train, which operates at the maximum speed of 200km/h, to conventional lines by the year of 2010. However, for the application of the tilting train to conventional lines, it is prerequisite to establish a stable turnout system allowing the tilting train to pass through it without reducing speed. Therefore, the improved turnout system for the speed-up of conventional lines has been developed and the prototype of the turnout system has been constructed. However, levels of impact-induced ground vibrations from the discontinuous part of the turnout system have not been clarified. In this study, analysis of ground vibrations around the improved turnout system is performed in order to predict the generation level of ground vibrations due to the passage of the tilting train through the improved turnout system.

A method has been described for tracking material interface in a 3-Dim, rectangular-grid, time-dependent, Eulerian hydrodynamics code. The accuracy is crucial to the overall accuracy of the simulations. A 2^nd order accuracy interface reconstruction method based on the Youngs' scheme has been implemented in our new dynamic FEM code. The method is applicable to the type of code in which the layout of materials is described solely by the volume fraction of the various materials in each computational cell. The volume fraction distribution is used to construct a plane interface in each mixed cell. The position of interface determines the flow across cell sides and hence enables volume fractions to be updated to the next time level. In this paper, the 2^nd order accuracy method has been compared with the new 1^st order accuracy method which we recently implemented based on the SLIC (Simple Line Interface Calculation).

We performed numerical analyses using an explicit code to evaluate the cumulative impact damage of an automotive aluminum front-end bumper back beam during low-speed crash events, as described by CMVSS215. we used a coupled numerical analysis scheme and considered the several fracture criterion such as EWK rupture model and plastic strain limit in the PAM-CRASH code to improve our damage and fracture estimates. Tensile test experiments for the notched and un-notched specimens were conducted to tune the performance of the EWK rupture model; The resulting material properties and fracture criterion were incorporated into the numerical analyses of the low-speed crash events. The simulation results were compared with the impact test.

As small form factor (one-inch and smaller) hard disk drives are widely used in portable consumer appliances and gadgets, their mechanical robustness is of greater concern. In the previous work, it is found that when the disk is more tightly clamped, it helps to decrease the shock response of the disk and then avoid the head slap. In this paper, the real boundary condition of the disk for a small form factor hard disk drive from Seagate is investigated numerically. The disk is clamped between the clamp and the hub. The shock response of the disk under a half-sine acceleration pulse is simulated by using the finite element method. In the finite element model, both contact between disk and clamp and contact between disk and hub are considered. According to the simulation results, how to decrease the shock response of the disk is suggested.

Combination of different materials used both in the projectile and the sandwich panel is getting more important in designing for maximization of energy absorption during impact. In the present study, we have simulated the bulging process during projectile impact for axisymmetric impact problems. We have discussed the bulging velocity tendency depending on some important geometrical and material parameters such as the yield strength, and tensile limit of the core for several different core thickness and different elapsed time after impact by using the AUTODYN commercial software. From our simulation, we have found that material properties have more dominant effects than the geometric properties on the bulging velocity.

A series of numerical simulations using SPH (Smoothed Particle Hydrodynamics) method were carried out to study the hypervelocity impact of aluminum spheres on multi-plate structures. Both the morphologic characteristics of debris clouds and the damage of intermediate plates were investigated. The possible damage effects of debris cloud threat on back wall were also described qualitatively. Results showed that, comparing with single plate or double-plate structures, the multi-plate structure has higher resistance capacity to the impact from hypervelocity particles. Hence the multi-plate shield structure has a better shielding performance with a reduction in weight of the structure. It provides a promising alternative to the traditional shield in the spacecraft shield design.

Radioactive material is used in the various fields. The numbers of transport for radioactive material have been gradually increased in both domestic and international regions. The safety of the cask should be secured to safely transport of radioactive material. The Korean atomic law and the IAEA safety standards prescribe regulations for the safe transport of radioactive material. The cask for spent fuel is comprised of the body and the impact limiter.

In this study, the empirical equation of the cask impact force was proposed based on the dimensional analysis. Using this empirical equation the characteristics of the impact limiter were analyzed. The results are also validated by comparing with the previous results of the impact area method and the finite element analysis. The present method can be used to predict the impact force of the cask.

Underwater experiments for an ideal explosive, TNT, and two nonideal explosives, CETR emulsion and DXD-04, were performed, and numerically simulated. For TNT, calculations done by using program-burn models based on the rate-independent Chapman-Jouguet theory were in a good agreement with experimental results, which validated the wide use of program-burn models for ideal explosives. For CETR emulsion and DXD-04, experimental observations could be reproduced with high precision only when reaction rates were employed. These results demonstrated that detonation in nonideal explosives can be modeled only by using properly calibrated reaction rates.

In this paper, the orbital forming simulation of an automotive hub bearing was studied to predict forming conditions and performances using the explicit finite element method. To set up an efficient solution technique for the orbital forming, axisymmetric finite element models and 3D solid element models were numerically solved and compared to each other. The time scaling and mass scaling techniques were introduced to reduce the excessive computational time caused by small element size in case of the explicit finite element method. It was found from the numerical results on the orbital forming that the axisymmetric element models showed the similar results to the 3D solid element models in forming loads whereas the deformations at the bearing inner race were quite different. Finally the strains at the bearing inner race and the forming forces of the peen were measured by test for the same product used in the numerical analysis, and were compared with the 3D solid element results. It was shown that the test results were in good agreements with the numerical ones.

Deformation rules and acoustic emission characteristics of granite under repeated loading-unloading are studied using the MTS Mechanics Testing System and Disp. acoustic emission instrument. It's found that the axial stiffness of granite as well as Poisson's ratio increases with the development of the plastic strain while the change trend of lateral stiffness is negative. For brittle rocks, strain is produced by three mechanisms: elastic deformation, axial micro-cracking and compaction. The peak AE rate is increasing with the plastic strain, which indicates that using the axial plastic strain as the internal damage variable to represent rock damage is reasonable.

Ceramic materials show good mechanical properties. However, the brittleness makes it difficult to predict their dynamic behavior of ceramic materials, and further the discrete nature of brittle failure requires a three-dimensional computation. In this paper, a computational model was developed for analyzing high velocity impact situations of brittle materials, incorporating with node separation scheme to describe the distinctive behavior of a brittle failure. This material behavior model was applied in a three-dimensional explicit code with Lagrangian description, which was developed to compute problems of dynamic brittle failure using four-node tetrahedral elements. To effectively handle the complex contact situations, involving multiple collisions and self-contact of severely deformed and fragmented bodies, careful considerations were paid to the global and local contact searching. In addition, an edge contact algorithm was developed to handle contacts between sharp edges. To validate the developed computational model and three-dimensional explicit code, oblique penetration into sandwiched ceramic plate by long rod was simulated, and the results were compared with experiments.

The authors have developed a new method of explosive welding using underwater shock wave for the welding of thin plate on a substrate. Considering the size limitation of the welding area in using the technique, the possibility of overlapping thin plates to make large-sized welding area is investigated. In general, the results for the welding of Inconel 600 on 304 stainless steel show a macroscopically successful weld, but the microstructure shows some melting spots caused due to the trapping of metal jet during the welding process when the welding condition is changed. The welding process is discussed based on the experimental results in comparison with some numerically simulated results obtained by AUTODYN-2D code.

A new technique has been developed to generate an extremely high impulsive pressure by using an explosive. A metal jet, typically observed in explosive welding is used in this technique. The behavior of metal jet is crucial to the design of pressure generator. The experimental observation was made by the collision of metal jet on a metal block surface. Many craters formed by the collision of metal jets on the surface of the metal block were observed. The craters were overlapped and distributed in a wide range. The diameter of the largest crater was 0.5 mm. The quantity of the discharged metal jets was found to be a function of the quantity of explosive. The total area of the craters is considered as proportional to the quantity of the discharged metal jets and the experimental conditions for the formation of large craters was investigated.

Impact welding has been carried out using a projectile having a diameter of 11 and 5 mm at an impact velocity of 200 m/s or more. A large projectile regardless of the slenderness ratio, was welded to a stainless steel target. However, only a small projectile with a slenderness ratio less than 1.2 was welded to the same target. In order to examine the effect of the diameter of the projectile on the weldability, the temperature elevating process in two cylindrical projectiles subjected to a longitudinal impact was evaluated numerically using LS-DYNA. The numerical results indicated that since the deformation mechanism of a projectile with a slenderness ratio less than 1.0 is different of that of the projectile with the slenderness ratio more than 1.5, the small projectile with the slenderness ratio less than 1.0 can be welded to the target.

Modeling of serrated chip formation is important to provide guidance for further development of this process and predict the quality of machined parts. The simulation of serrated chip formation is hard to achieve due to the lack of a proper material model which represents real phenomenon within a narrow adiabatic shear band. In the present study, a material constitutive law containing strain hardening and thermal softening was proposed to predict adiabatic shear localization within serrated chips. The outcomes of FEM simulation show the capability to predict serrated chip formation. The effective strain distributions and the forces are computed within this study.

Nickel-aluminides-reinforced nickel-matrix composites were fabricated from 0.05mm-thick nickel foils and 0.012mm-thick aluminum foils, in a process using a pulsed-current hot pressing (PCHP) equipment, and the effect of reaction temperature on mechanical properties of the composites was investigated. The composites were of laminated structure and composed of Ni and reacted layers containing Ni-aluminides. The chemical composition of the reacted layers was dependent on reaction temperature in the temperature range employed. Tensile testing at room temperature revealed that the reaction temperature evidently influences mechanical properties, including tensile strength, elongation and fracture mode, of the composites. The tensile strength and elongation of composites fabricated at 1373K were 500MPa and 3.8%, respectively. Microstructure observations of fractured specimens revealed that Ni layers of the composite played a significant role in prohibiting the growth of numerous cracks emanating from Ni-aluminides. In the case of composites fabricated at 1373K, in addition, crack propagation between Ni-rich Al-solid-solution layers and cellular Ni₃Al in the Ni-aluminides were prevented by mutual interaction.

When cavitation bubble is collapsed, shock wave which can deform metallic materials is produced. Cavitation impacts can be used for surface modification to enhance fatigue life of metallic materials in the same way as shot peening. As a peening method using cavitation impact does not require shots in shot peening, it is called “cavitation shotless peening CSP”. Although CSP can introduce compressive residual stress, i.e., macro-strain into metallic materials, full width at half maximum of diffractive X-ray profile was decreased by CSP. In the present paper, tool alloy steel for forging die was chosen as tested material to investigate mechanism of improvement of fatigue life, as CSP improved the life time of the forging die. The introduction of macro-strain was revealed by measuring residual stress, which was evaluated by X-ray diffraction method. The fatigue life was investigated by using a plate bending fatigue test changing with processing time of CSP. The micro-strain was evaluated by a fundamental parameter approach, which is one of X-ray diffraction method. It was concluded that the fatigue life of the steel was improved about 90 times by CSP and CSP can introduce macro-strain, i.e., compressive residual stress and releasing micro-strain. The micro-strain becomes about 1/20 of heat treated specimen by CSP.

Gd-doped ceria nano powder(~5 nm) was shock-loaded by a plate impact experiment using a single stage light gas gun. A computational model was used to simulate the shock state (pressure and density changes along time) of the sample in two dimensional Eulerian code. The predicted density of compacted sample from the simulation was about 90%. To reveal the effect of shock compaction on sintering behavior, the recovered sample was heat-treated and the microstructure was compared with that of a conventionally compacted and heat-treated sample.

Dry zinc coating processes similar to the shot pinning was studied in the aspects of environmentally benign process to substitute traditional wet type phosphate coating of the work-piece, which is for protection from the deterioration of the surface quality and the shortening of the lifetime of the die during cold extrusion. Experiment and simulation on the collision and coating process of the zinc coated steel balls onto the steel target was performed. Coating patterns on the target and damage of the zinc shell of the ball with respect to the colliding speed were observed during the experiment. Explicit finite element analysis showed the deformation and the fracture of the zinc shell were similar to the experimental results even though the adhesion of the zinc layer onto the work-piece could not be expressed directly. The optimal velocity of the balls was obtained considering effective zinc coating and maximum lifetime of the ball.

In this study, dynamic impact analysis for the passenger air-bag(PAB) module has been carried out by using FEM to predict the dynamic characteristics of vehicle ride safety against head impact. To carry out the dynamic analysis of head impact test of the PAB module assembly of automobile, the FE models, which are consist of instrument panel, PAB Module, and head part, are combined to the whole module system. Then, impact analysis is carried out by the explicit solution procedure with assembled FE model. And the dynamic characteristics of the head impact are observed to prove the effectiveness of the proposed method by comparing with the experimental results. As a result, the better optimized impact characteristics are proposed by changing the tie bracket's width and thickness of module. The proposed approach of impact analysis will provides an efficient vehicle to improve the design quality and reduce the design period and cost.

A study about the response of motorcycle helmets to impacts is described in this paper and possible ways to improve current designs are discussed. Firstly, a simple unidimensional model of helmet is analyzed and the main parameters that affect its response are pointed out. Subsequently, the generation and testing of the Finite Element model of a commercially available helmet are described and numerical results are compared to experimental results. Finally, the FE modeled is used to compare different design configurations.

The tensile properties of YAG laser welded butt joints using different high strength steel sheets with a tensile strength of 270 MPa, 590 MPa and 980 MPa (denoted HR270, HR590 and HR980, respectively) were investigated at static and dynamic rates, together with the three kinds of laser welded joints made by the same steel sheets. The impact tensile tests were performed by using the vertical type of split Hopkinson tension bar apparatus, while the static tensile tests were carried out using a universal testing machine INSTRON5586. The impact tensile strengths were significantly increased in comparison with the static ones due to the effect of strain rate, which might be the contribution of the part of HR270 base metal. And in both of static and impact tests, the fracture strains of HR270-HR590 joint, HR270-HR980 joint and HR590-HR980 joint were about one half of the fracture strains observed in the same steel welded joints of HR270-HR270, HR270-HR270 and HR590-HR590, respectively.

This study discusses a head injury mechanism in case of a human head subjected to impact, from results of impact experiments by using a physical model of a human head with high-shape fidelity. The physical model was constructed by using rapid prototyping technology from the three-dimensional CAD data, which obtained from CT/MRI images of a subject's head. As results of the experiments, positive pressure responses occurred at the impacted site, whereas negative pressure responses occurred at opposite the impacted site. Moreover, the absolute maximum value of pressure occurring at the frontal region of the intracranial space of the head model resulted in same or higher than that at the occipital site in each case that the impact force was imposed on frontal or occipital region. This result has not been showed in other study using simple shape physical models. And, the result corresponds with clinical evidences that brain contusion mainly occurs at the frontal part in each impact direction. Thus, physical model with accurate skull shape is needed to clarify the mechanism of brain contusion.

In the present study, the bending collapse of an elastoplastic cylindrical tube subjected to static pure bending is investigated using the finite element method (FEM). The moment of the elastoplastic cylindrical tube is controlled by the flattening rate of the tube cross-section. For a long tube, the flattening rate can be expressed in terms of the axial and circumferential stresses that, in turn, depend on the material and geometrical properties and the curvature of the tube. On the other hand, for a short tube, the boundary condition of the fixed walls prevents the flattening rate. In order to account for the length effect of tubes, we propose a new method in which flattening is considered as a deflection problem of a fixed curved beam. The proposed method was able to predict the change in the flattening rate as the curvature was increased. A rational prediction method is proposed for estimating the maximum bending moment of cylindrical tubes that accounts for the length effect. Its validity is demonstrated by comparing it predictions with numerical results obtained using the finite element method.

In this paper, a new type of honeycomb structure is proposed to enhance the energy absorption capacity for a honeycomb structure, and investigated its energy absorption efficiency (absorbed energy per unit volume) by finite element method (FEM). This model has small arc-shaped parts on the double cell wall, and can be manufactured by a similar way of standard honeycomb structures. Also, the proposed structure has large rigidity of plastic bending without increasing the mass. In this paper, effects of geometrical properties on the energy absorption characteristics are discussed.

As a next-generation metropolitan transportation means, nowadays non-step bus is in the spotlight world widely. However, in the design of non-step bus, the most important consideration should be focused on the securing of the survival space for passengers in unexpected traffic accident. In this context, this paper presents the finite element analysis of the rollover and head-on crash response of a composite non-step bus. A 3-D full-scale finite element model of the non-step bus, together with the simulation conditions which are consistent with the safety test rules established in Europe, is employed for the realistic and reliable numerical analysis.

Neck injury in rear-end car collisions is an increasing concern in the field of traffic safety. This injury commonly occurs at rear-end impact, however the injury mechanisms for whiplash remain a mystery. The purpose of this study is to quantitatively analyze the head and neck kinematics during the low-speed rear-end impact of automobiles. It is important to produce data that is related as closely as possible to the in vivo situation. So, we performed a sled test which simulated rear-end impacts with a velocity of 0.6 m/s with five normal healthy male subjects. 3-D motion analysis system was used to document motion data of two situations. When we compare the values of angular velocity and acceleration of head and neck, the peak magnitudes of inclined seated posture were smaller than those of upright seated posture. The result of this study is expected to provide insight that will aid in determining the mechanism of whiplash which is crucial to the identification of possible injury mechanisms.

Safety of the occupant during the crash is very essential design element. Many researches have been investigated in reducing the fatal injury of occupant. They are focusing on the development of a dummy in order to obtain the real human-like motion. However, they have not considered the arm resist motion during the car accident. In this study, we would like to suggest the importance of the reactive force of the arm in a car crash. The influences of reactive force acting on the human upper extremity were investigated using the impedance experimental method with lumped mass model of hand system and a Hybrid III dummy with human-like arm. Impedance parameters (e.g. inertia, spring constant and damping coefficient) of the elbow joint in maximum activation level were measured by free oscillation test using single axis robot. The results showed that without seat belt, the reactive force of human arm reduced the head, chest, and femur injury, and the flexion moment of the neck is higher than that of the conventional dummy.

The characteristics of flexor reflexes have been investigated in the previous studies with human subjects who were seated or supine position. However, researchers did not describe how the spinal circuits are used in different hip angles for paralyzed subjects, such as the standing position with walker or cane. In upright posture the compatibility between a flexor reflex of leg and body balance is a special problem for lower limb injured subjects. Therefore, the purpose of this study was to investigate the effects of hip angle change on the flexor reflex evoked in standing paralyzed subjects supported by walker. In this study, six spinal cord injured and four stroke subjects were recruited through the inpatient physical therapy clinics of Korea national rehabilitation hospital. A single axis electronic goniometer was mounted on the lateral side of the hip joint of the impaired limb to record movements in the sagittal plane at this joint. The electronic goniometer was connected to a data acquisition system, through amplifiers to a computer. Since subject' posture influenced characteristics of the flexion reflex response, the subjects were supported in an upright posture by the help of parallelogram walder. Two series of tests were performed on each leg. The first series of the tests investigated the influence of hip angle during stationary standing posture on flexion reflex response. The hip angle was adjusted by the foot plate. The second examined the effect of the voluntary action of subject on swing motion during the gait. The electrically induced flexion reflex simultaneously produced the flexion of the hip, knee and dorsiflexion of the ankle enabling the swing phase of walking. Form the experimental results we observed that the reflex response of hip joint was largerwith the hip in the extended position than in the flexed position during standing posture. Under voluntary movement on flexion reflex during gaint, the peak hip angle induced by stimulation was increased in spinal cord injury and stroke patients by subject' voluntary movement.

Taekwondo is a martial art form and sport that uses the hands and feet for attack and defense. Taekwondo basic motion is composed of the breaking, competition and poomsea motions. The side kick is one of the most important breaking motions. The side kick with the front foot can be made in two steps. In the first step, the front foot is extended forward from the back stance free-fighting position. For the second step, the rear foot is followed simultaneously. Then, the side kick is executed while the entire body weight rests on the rear foot. In this paper, the impact analysis on a human model for kicking posture was carried out. The ADAMS/LifeMOD used numerical modeling and simulation for the side kick. The numerical human models for assailant and opponent in competition motion were developed. The maximum impact force on the human body was obtained by experiment and was applied to impact simulation. As a result, the impact displacement and velocity of the numerical human model were investigated.

The complete evaluation of the side vehicle structure and the occupant protection is only possible by means of the full scale side impact crash test. But, auto part manufacturers such as door trim makers can not conduct the test especially when the vehicle is under the developing process. The main objective of this study is to obtain the design guidelines by a simple component level impact test. The relationship between the target absorption energy and impactor speed were examined using the energy absorbed by the door trim. Since each different vehicle type required different energy levels on the door trim. A simple impact test method was developed to estimate abdominal injury by measuring reaction force of the impactor. The reaction force will be converted to a certain level of the energy by the proposed formula. The target of absorption energy for door trim only and the impact speed of simple impactor are derived theoretically based on the conservation of energy. With calculated speed of dummy and the effective mass of abdomen, the energy allocated in the abdomen area of door trim was calculated. The impactor speed can be calculated based on the equivalent energy of door trim absorbed during the full crash test. With the proposed design procedure for the door trim by a simple impact test method was demonstrated to evaluate the abdominal injury. This paper describes a study that was conducted to determine sensitivity of several design factors for reducing abdominal injury values using the matrix of orthogonal array method.

In conclusion, with theoretical considerations and empirical test data, the main objective, standardization of door trim design using the simple impact test method was established.

Metallic glasses are amorphous meta-stable solids and are now being processed in bulk form suitable for structural applications under impact loading. Bulk metallic glasses have many unique mechanical properties such as high yield strength and fracture toughness, good corrosion and wear resistance that distinguish them from crystalline metals and alloys. However, only a few studies could be found mentioning the dynamic response and damage of metallic glasses under impact or shock loading. In this study, we employed a small explosive detonator for the dynamic indentation to a Zr-based bulk amorphous metal in order to evaluate the damage behavior of bulk amorphous metal under impact or shock loading conditions. Results were compared with those of spherical indentation under quasi-static and impact loading and were discussed. The interface bonded specimen method was adopted in order to observe the subsurface damage, especially the formation of shear bands induced during indentation under different loading conditions.

The present study is to fabricate dense tricalcium phosphate (TCP) compacts by our newly developed underwater-shock consolidation technique and to investigate the characteristics of the compacts. By adding Al₂O₃ powder to β-TCP powder, the biocomposites were fabricated to improve the fracture toughness. Sound compacts of α- and β-TCP powders and β-TCP/Al₂O₃ biocomposite powder were fabricated without any cracks and tears. The relative densities of α- and β-TCP compacts were about 85% in as-compacted state and more 94% after annealing at 1373K for 7.2ks. Compressive strengths of α- and β-TCP compacts are 160 and 140MPa after annealing at 1373K for 7.2ks, respectively. Compressive strength and fracture toughness of β-TCP/Al₂O₃ biocomposites after annealed at 1373K for 7.2ks were 188MPa and 2.54MPa·m^1/2, which are comparable to values of human bone, respectively.

Since wear of the polyethylene (Ultra High Molecular Weight Polyethylene or UHMWPE) acetabular cup is considered to be the main cause of loosening of the artificial hip joint, the cross-linked UHMWPE with high durability to wear has been developed. This paper deals with impact load transmission through the complex of an artificial hip joint consisting of a UHMWPE acetabular cup (or liner), a metallic femoral head and stem. Impact compressive tests on the complex were performed using the split-Hopkinson pressure bar apparatus. To investigate the effects of material (conventional or cross-linked UHMWPE), size and setting angle of the liner, and test temperature on force transmission, the impact load transmission ratio (ILTR) was experimentally determined. The ILTR decreased with an increase of the setting angle independent of material and size of the liner, and test temperature. The ILTR values at 37°C were larger than those at 24 °C and 60°C. The ILTR also appeared to be affected by the type of material as well as size of the liner.

To investigate the dynamic deformation behavior of silicon induced by the energetic cluster impact at an atomistic level, cluster impact simulations are carried out using molecular dynamics. Clusters are emitted to the silicon (100) surface with external kinetic energies varying from 1 to 10 eV/atom. While a structural phase transformation is identified as the dominant deformation mechanism in silicon due to the increased pressure caused by the energetic cluster impact, its deformation pathway tends to change according to the kinetic energy of cluster. In the lower energy region, the initial diamond structure of silicon is first transformed into the beta-tin structure during the impact process, and then this high-pressure structure is transformed into an amorphous structure after the impact process is completed. This result is very similar to those computed in the quasi-static deformation. On the other hand, amorphous structures are directly transformed from initial diamond structure in the higher energy region. Additionally, the propagation of the shock-wave is accompanied in this deformation.

In this paper we analyzed correlation between geometrical character and resistance, and effective horse power by using Pearson correlation coefficient which is one of the data mining methods. Also we made input data to ship's geometrical character which has strong correlation with output data. We calculated effective horse power and resistance by using Neuro-Fuzzy system. To verify the calculation, 9 of 11 container ships' data were improved as data of Neuro-Fuzzy system and the others were improved as verification data. After analyzing rate of error between existing data and calculation data, we concluded that calculation data have sound agreement with existing data.

Silk films prepared from regenerated silk fibroin are normally stabilized by β-sheet formation through the use of solvents (methanol, water etc.). Herein, we report a new method of preparing water-stable films without a β-sheet conformation from regenerated silk fibroin solutions by incorporating a small amount (0.2 wt%) of multiwalled carbon nanotubes (MWCNTs). To extend the biomaterial utility of silk proteins, forming water-stable silk-based materials with enhanced mechanical properties is essential. Scanning electron microscopy and transmission electron microscopy were used to observe the morphology of the MWCNT-incorporated silk films. The wide-angle X-ray diffraction provided clear evidence of the crystallization of the silk fibroin induced by MWCNT in the composite films without any additional annealing processing. The tensile modulus and strength of the composite films were improved by 108% and 51%, respectively, by the incorporation of 0.2 wt% of MWCNTs, as compared with those of the pure silk films. The method described in this study will provide an alternative means of crystallizing silk fibroin films without using an organic solvent or blending with any other polymers, which may be important in biomedical applications.

Starting from the derivation of an analytical method to expand measured static displacement data to full degrees of freedom, this study proposes a damage detection method to detect the damage of damaged beam by introducing displacement curvature and damage factor (DF). The validity of the proposed method is evaluated in damaged beam system that two simple beams are perpendicularly interconnected at a point.

Strength degradations in silicon nitride ceramics subject to damage from contact with hard spheres are investigated. Strengths against indentation load, number of cycles in contact, or stress-rate parameter are reported and compared with theoretical models. Silicon nitride ceramics are prepared by nitride pressureless sintering (NPS) process, which process is the continuous process of nitridation reaction of Si metal combined with subsequent pressureless sintering. Microstructure characterizations reveal silicon nitride fabricated by NPS process exhibits a quasi-plastic mode, with continuous strength loss beyond a load above the onset of yield, and falloff at high number of cycles, > 10⁵ at contact load, P = 950 N, using WC sphere r = 1.98mm. The strength degradation is substantially faster by dynamic fatigue. Failures originated from contact damages, quasi-plastic microcrack zones, with developing radial cracks during strength test. The implication is that quasi-plastic damage of NPS silicon nitride itself can preserve benefits from the inherent higher damage tolerance at lower number of cycles of contacts, but fatigue susceptibility at multicycle contacts and lower stressing rate.

Polyamide powders were prepared as the laser sintering materials for the three-dimensional duplication equipment of selective laser sintering process. Though polyamide powders had a similar chemical structure, there were big differences in thermal properties, particle size and distribution, and shape. These variations had a close relation with the processibility of laser sintering. As far as the particle shape approached a spherical shape, the processibility of laser sintering was improved. The particle size distribution also played an important role in the precision of fabrication.

A Solid Freeform Fabrication (SFF) system using Selective Laser Sintering (SLS) is currently recognized as a leading process and SLS extends the applications to machinery and automobiles due to the various materials employed. Especially, accuracy and processing time are very important factors when the desired shape is fabricated with Selective Laser Sintering (SLS), one of Solid Freeform Fabrication (SFF) system. In the convectional SLS process, laser spot size is fixed during laser exposing on the sliced figure. Therefore, it is difficult to accuracy and rapidly fabricates the desired shape. In this paper, to deal with those problems a SFF system having ability of changing spot size is developed. The system provides high accuracy and optimal processing time. Specifically, a variable beam expander is employed to adjust spot size for different figures on a sliced shape. Therefore, design and performance estimation of the SFF system employing a variable beam expander are achieved and the mechanism will be addressed to measure the real spot size generated from the variable beam expander. Also, the reduction of total processing time is an important issue in SFF system. A digital mirror system (DMS) is a system which scans the laser beam with different spot size. The spot size is selected based on the slicing section to decrease and accuracy of the process time and improve the processing efficiency. In this study, the optimal scan path generation for DMS will be addressed, and this development will improve the whole processing efficiency and accuracy through the scan efficiency by considering the existing scan path algorithm and heat energy distribution.

Recently, Study of 3D freeform fabrication method was working in the various applications. For example, in the powder base, it's laminated using a binding method or laser sintering method. However, the demerits of these methods are to take long time for post process and not enough to keep high strength of manufacturing part. The binding method needs the post process and the time for post process needs longer time than a manufacturing time. The sintering method has huge size of system with module of the laser. In this paper, we introduce a method of 3D freeform fabrication using a curing of photopolymer resin. A photopolymer curing method has simply fabrication process and high strength of manufacturing part. So, we are configuration the system with compact type module for the office environment and experiment a UV curing test with photopolymer resin in the 3D freeform fabrication method. In the conclusion, we fabricate the 3D freeform part, which is suitable to the office environment using a photopolymer curing method.

This experimental study investigates the fracture characteristics of the camshaft made with newly developed SM53C material. As part of the countermeasure, use the surface hardening heat treatment. Cam shaft which is a part of automobile engine is very essential when traveling and significant to fuel injection timing. Stiffness and efficiency are important for automobile sash which have a durability of the engine. High hardness and durability are necessary, because engine output is affected by cam shaft directly. So, high-frequency induction hardening is very important because of increasing the surface strength. The shape of hardening depth, hardened structure, hardness, and fracture characteristics of SM53C composed by carbon steel are also investigated.

The freezing and thawing cycles tests were conducted on red sandstone and shale. In this paper, freezing-thawing damage propagation processes are analyzed, and two deterioration modes, i.e. scaling mode for red sandstone and fracturing mode for shale, are suggested. The uniaxial compression tests are also conducted on the two types of rock subjected to different freeze-thaw cycles at room temperature. It is shown that the uniaxial compression strength and the elastic modulus of rocks at low-temperature depended on the number of freeze-thaw cycles. The mechanism and influence factors of rock deterioration due to freeze-thaw are analyzed, and the damage process of rock should be divided into two coupled parts: rocks damage due to freeze-thaw cycle as well as the damage propagation caused by stress erosion. The damage evolvement equations for the two rocks are established, and the constitutive equations for the two types of rock subjected to freeze-thaw are deduced, accordingly. It is approved that the constitutive model considering the freeze-thaw damage is credible and can be used for the following theory analysis.

Cold forging of pinion gear with shape of outer spur gear and inner helical gear have been investigated in this study. A numerical analysis for preform design substituting cutting process in gear forging was developed by means of upsetting process. By using the finite element program DEFORM-3D, the analysis is carried out. Using this simulation, the preform of pinion and helical gear forging process were designed. The suggested process is verified by experiment. Compared to the traditional CNC processing, the upsetting process can form a preform without cutting, which leads to shorter forming time and reduce material usage.

Scanning probe lithography such as direct–writing lithographic processes and nanoscratching techniques based on scanning probe microscopy have presented new micromachining methods for microelectromechanical system (MEMS). In this paper, a micromachining system for thermal scanning probe lithography is introduced, which consists of the cantilever arrays and a big stroke micro XY–stage. A large machining area and high machining speed can be realized by combining arrays of cantilevers possessing sharp tips at their top with the novel micro XY–stage which can obtain big displacements under relatively low driving voltage and in a small size. According to the above configuration, this micromachining system is provided with high throughputs and suitable for industrialization due to its MEMS–based simple fabrication process. The novel micro XY–stage applied in this system is presented in detail including the unique structure and principles, which shows an obvious improvement and distinct advantages in comparison with traditional structures. It is analyzed by mathematical model and then simulated using finite element method (FEM), it is proved to be able to practically serve the micromachining system with high capability.

To expand an inevitably limited rotating range of the existing planar precision stage, we suggest a revolving stage driven by three-separate axial type of transverse flux induction motors spaced 120° apart. It is a non-contact integrated rotating system that uses three-axial vector forces such as normal and thrust force of each motor. In this paper, the primary principles capable of realizing such a contact-less revolving stage are reviewed and compared, with results that seem to confirm the main principles of the suggested system. And then, the positioning method with only the air-gap measurements covering full degree of freedom is presented, compared with that of existing stages.