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Laser-based surface enhancement techniques improve metals’ mechanical properties. Laser Hardening (LH) and Laser Shock Peening (LSP) techniques are effective particularly well with low-alloy steel made of 34Ni-Cr-Mo6, which is a type of steel alloy that is put to use in a wide variety of fields because it possesses excellent levels of both strength and toughness. For specific applications, the laser can be shaped into line or spherical beams. On the other hand, typical industrial requirements of low alloy steel components like 34Ni-Cr-Mo6 are enhanced hardness and mechanical strength with minimum or no distortion. A 3 kW high power fiber laser with a flat top-hat beam of dimension $30\times 1$mm and a circular beam of Ø6mm are employed in this study. Investigation into the effects of repeated LSP on the microstructures and residual stress of 34Ni-Cr-Mo6 low alloy steel was also done. LSP treatment is carried out at 6.36GWcm${}^{-2}$ Laser Power Density (LPD) with different laser impacts, i.e. single and double, by keeping 0% overlap along the scanning direction and perpendicular directions, respectively. The shock-peened samples were characterized in terms of residual stress measurements and microstructural evolution using different characterization techniques. A substantial improvement in compressive residual stress was observed at the hardened cross-section i.e. $\sim -260$MPa and at shock peened surface $\sim -620$MPa respectively as compared to the as-received sample ($\sim -100$MPa). LH samples showed a better result in terms of microhardness values when compared to shock peened samples i.e. for LH, the microhardness values at the cross-section were $\sim 710\pm 40$HV${}_{0.5}$ nearly 2.5 times increase in hardness. Extreme plastic deformation was found by microstructural examination of cross-sections of LSP-treated areas. Hardness was nearly marginally improved in multiple times LSP-treated samples compared to unpeened ones as a result of LSP.

To evaluate the effect of coatings on the fatigue behaviors of turbine rotor steel, TiN and TiAlN films were deposited on the 1Cr-1Mo-0.25V steels by arc-ion plating (AIP) method with and wihtout screen ion filter. The coating thickness were varied with 2.5 μm, 3.5 μm, and 5.0 μm. A Cu-Kα beam source was used as a characteristic X-ray and the crystal plane of (422) was selected to evaluate the residual stresses. In order to clear the relationship between fatigue behavior and residual stress of specimen coated with TiN and TiAlN films, the fatigue tests of specimens with and without coating were carried out at room temperatures respectively. It is shown that the fatigue life of the coated specimen was longer than that of uncoated specimen. The compressive residual stresses on the coatings were higher, and the fatigue crack initiated at an inclusion in the substrate near bond interface. It is known that compressive residual stress caused by hard coating would retard the fatigue crack initiation on the specimen surface, and then led to fatigue strength and fatigue life increasing.

In this study, path-independent values of the J-integral in the finite element context for an arbitrary three-dimensional interface crack configuration in welds of dissimilar steels are presented. For the fracture mechanics analysis of an interface crack in welds of dissimilar steels, residual stress analysis and fracture analysis must be performed sequentially. In the analysis of cracked bodies containing residual stress, the usual domain integral formation results in path-dependent values of the J-integral. And unlike cracks in homogeneous materials, an interface crack in welds of dissimilar steels always induces both opening and shearing modes of stress in the vicinity of the crack tip. Therefore, this paper discusses modifications of the conventional J-integral that yield path independence in the presence of residual stress and the total J values which can characterize the severity of an interface crack tip in welds of dissimilar steels. A finite element method which can evaluate the J-integral for an interface crack in three-dimensional residual stress bearing bodies is developed using the modified J-integral definition and total J values. The situation when residual stresses only are present is studied as is the case when mechanical stresses are applied in conjunction with a residual stress field.

The advanced piezoelectric ceramic composite actuator, which is called LIPCA (LIghtweight Piezoelectric Composite Actuator), replaced the Al foil and stainless steel in THUNDER with the FRP and the optimization of the laminate configuration was performed to maximize the stress transfer and the fiber bridging effect. This study evaluated the fatigue characteristics in LIPCA under the resonance frequency, and the changes of its interlaminar phase were also evaluated. Beside, the residual stress distribution was estimated. In conclusions, firstly, comparing with the fatigue life of LIPCA without the artificial delamination (intact LIPCA), the fatigue life of LIPCA embedded by the artificial delamination was decreased up to 50%. Secondly, the micro void growth and the coalescence of epoxy were actively made at the interlaminar phase subject to the large tensile stress. Finally, it was known that the harmonic configuration between the compressive residuals stress and the tensile one was made. The requirement of the performance displacement increment was satisfied.

Wings for the defense industry such as fighters, missiles, and rockets should show no deformation or damage on the structure. The structures of existing wings had holes for weight reduction. The plates and frames were fixed with rivets or screws, which limited the weight reduction possible. In this study, an improvement was made in jointing methods through EB welding and laser welding. Welding strength was measured through tension testing. In addition, finite element analysis was performed for the welding process so as to deduce the optimum welding condition.

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.

This study is focused on the fatigue properties of automobile high-strength bolts, including the effect of mean stress level, pre-processing schedule and the residual stresses. And the mean stress levels are 0.3, 0.5 and 0.7 times to the tensile strength (σ_B) of the material respectively. The main results obtained are as follows: 1) the fatigue strength increases under the mean stress loading, but the differences between the loading levels are not so evident; 2) most of the cases in this study are broken from the bottom of the screw thread, and the crack initiated from the impurities.

Microwire made using a straightening process has high added value and has been adopted in many fields of industry. There is much active research on the straightening process. Very straight microwire can be obtained by removing the residual stress induced during the manufacturing process. Generally, the residual stress is removed or minimized through several drawing steps with heat treatment. This study used finite element analysis to calculate the residual stress during each straightening process and investigated the main reason for a change in stress.

High-speed steels are generally used for the cutting of other hard materials. These are hard materials, and can be used at high temperatures. Therefore, some of them are used for warm metal forming such as forging. However, in the tools used in hot working, an excellent hot hardness and long-life fatigue are strongly required. In the present study, the influence of shot peening on the surface characteristics of high-speed steels was investigated. Shot peening imparts compressive residual stresses on the metal surface, thus improving the fatigue life of the machine parts. In the experiment, the shot peening treatment was performed using an air-type shot peening machine. The shots made of cemented carbide were used. The workpieces were two types, W-type and Mo-type alloys. Surface roughness, compressive residual stress, and hardness of the peened workpieces were measured. It was found that shot peening using the hard shot media was effective in improving the surface characteristics of high-speed steels.

Plastics is commonly used in consumer electronics because of it is high strength per unit mass and good productivity, but plastic components may often become distorted after injection molding due to residual stress after the filling, packing, and cooling processes. In addition, plastic deteriorates depending on various temperature conditions and the operating time, which can be characterized by stress relaxation and creep. The viscoelastic behavior of plastic materials in the time domain can be expressed by the Prony series using the ABAQUS commercial software package. This paper suggests a process for predicting post-production deformation under cyclic thermal loading. The process was applied to real plastic panels, and the deformation predicted by the analysis was compared to that measured in actual testing, showing the possibility of using this process for predicting the post-production deformation of plastic products under thermal loading.

The microplastic deformation behavior of 20 vol.% SiCp/Al composites with various SiC particle sizes were investigated. The SiC particles are in four nominal sizes of 1, 5, 20 and 56 µm. The experimental results showed that the micro-yield strength is very sensitive to composite microstructure features. As the particle size increases, the micro-yield strength of composites decrease firstly, and then increase. The observed results were attributed to thermal residual stress and dislocation density due to the large difference in coefficient of thermal expansion between the matrix and reinforcement.

In this study, three types of functionally graded Al₁₈B₄O₃₃/Mg composites which consisted of 2, 3 and 4 layers and where volume fractions of Al₁₈B₄O₃₃ were gradually changing from 0 to 35% were fabricated using squeeze infiltration technique. The mechanical parameters of each layer were measured for the analysis of residual stress. Elastic finite element numerical models were applied to the analysis of thermal residual stress. The analytic results showed that the residual stresses were significantly decreased in the macrointerface with increasing the number of layer.

In the present paper we consider two representative methods for residual stress evaluation at the micro-scale: a (semi-)destructive method involving material removal and the measurement of strain relief; and a non-destructive X-ray diffraction technique involving the use of micro-focused synchrotron X-ray beam. A recently developed strain relief approach is described using a Focused Ion Beam (FIB) to create a circular trench of progressively increasing depth around a circular "island". Residual stress is evaluated by the comparison of the strain relief (measured by digital correlation of displacements or strains) with Finite Element simulations. The technique is illustrated for a thin TiN coating layer. The second approach uses focused synchrotron X-ray beams for white beam Laue diffraction. Demonstration experiments described involve in situ loading of commercially pure nickel foil. Procedures for validation and improvement of accuracy are discussed.

Fe-Ga thin films were prepared by DC magnetron sputtering on Si (100) substrate and an alloy target consisting of Fe₈₁Ga₁₉ was used. X-ray diffraction techniques were used to quantify the strain in the Fe-Ga thin films by measuring the interplanar spacings of select crystallographic planes. The interplanar spacing, d, for the family of Fe-Ga {211} planes was measured. Using the well-established sin²ψ technique, the residual stress of the Fe-Ga thin films was calculated. It has been found that the stress for Fe-Ga thin films quickly increases with increasing the sputtering power. The residual stress of thin films is almost unchanged in the range of 220-440 nm, and then it decreases with increasing the thickness of thin films.

Since the thin film technology is applied to micro-machines, MEMS (micro electro-mechanical system), optical devices and others, the evaluation of mechanical properties in thin films becomes to be important. On the other hand, there are differences in mechanical properties between bulk materials and thin films, but studies in this field have not yet been made enough. The present paper reports on the evaluation of the mechanical properties of Cu thin films with and without AlN passivation layer. Specimens with different thickness of Cu film were subjected to cyclic plane bending fatigue test. Residual stresses developed in the Cu films were measured in a sequence of bending cycles using X-ray diffraction method in order to understand the effect of film thickness and passivation layer on mechanical properties of Cu thin films.

Reactor coolant loop (RCL) pipes circulating the heat generated in a nuclear power plant consist of so large diameter pipes that the installation of these pipes is one of the major construction processes. Conventionally, a shield metal arc welding (SMAW) process has been mainly used in RCL piping installations, which sometimes caused severe deformations, dislocation of main equipments and various other complications due to excessive heat input in welding processes. Hence, automation of the work of welding is required and narrow-gap welding (NGW) process is being reviewed for new nuclear power plants as an alternative method of welding. In this study, transient heat transfer and thermo-elastic-plastic analyses have been performed for the residual stress distribution on the narrow gap weldment of RCL by finite element method under various conditions including surface heat flux and temperature dependent thermo-physical properties.

Multi-layer diamond-like carbon (DLC) coating, 150 and 220 nm thick were deposited by negative pulsed d.c. bias induced with magnetron sputtering. The objective of this research is to resolve a wear resistance in terms of DLC coating residual stress and mechanical properties. The bias was controlled from - 200 to 0 V during 10 second with point contacting controller. The surface structure was continuously fabricating to soft and hard-layer during deposition. It was shown that the compressive residual stress and hardness were 0.09, 18 GPa under multi-layer coating condition. The as-deposited DLC coating has a relatively higher wear resistance than unmodified DLC under nanoabrasive wear. It also showed that multi-layer DLC coating had no wear until 400 nN. The decreased residual stress and increased film hardness in the multi-layer coating gave a rise to increase wear resistance.

Today, ships and structures are becoming larger (large structures, vessels, FPSO, etc.). Thus, high-strength welding material is required. The advantages of welding over other joining methods, depending on the development of welding technology, include such things as ease of operation and the structures of simplification and the confidential excellence, etc. However, shrinkage and deformation also occur, because of the repeated heating and cooling. Welding residual stress has an adverse effect on stability, but, it was closely related fatigue strength and brittle fracture of structures. In this study, experimental and analysis were conducted, and AIS3000 used to measure residual stress, which were compare with ANSYS analysis results. Metal surface microstructure was observed at various weld spots, as well as HAZ, and base metal using the optical microscope, and component analysis and crystal plane were measured using an XRD and EPMA.

Certain high-speed trains often suffer from the erosion of wind-drift sand during the serving period. The present paper simulated this sand-blasting process with consideration of sand-blasting pressure, angle, distance and sand particle size representing different natural conditions. Results show that the grit size has the greatest influence on roughness and residual stress of the 7N01 aluminum alloy based on the orthogonal test. The samples after low intensity sand-blasting (LISB) were characterized by micro-hardness, surface morphology and fatigue test. Results show that the surface of the blasted sample was severely impinged in form of extruded ridges crater-like morphology, representing different roughness values. The LISB causes a similar spoon shape residual stress distribution along the depth direction and it also increases the hardness of the surface zone. Finally, the residual compressive stress plays an important role in the improvement of the fatigue life, and the increase of roughness can seriously shorten the fatigue life.

The welding residual stress has different effects on the mechanical properties of aluminum alloy welded joints, such as size stability, fatigue strength and stress corrosion cracking. Therefore, it is very important to evaluate the welding residual stress accurately. In this paper, the residual stress of A7N01 aluminum alloy welded joints was measured by X-ray diffraction. In contrast to the traditional method, the cos$\alpha$ method was used in this paper, the results were compared with those obtained by the conventional ${sin}^2\psi$ method. In addition, the influence of oscillation unit on the test results of the cos$\alpha$ method was studied.