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Aluminum alloys are widely used in the automotive and aerospace industries due to their lower mass-to-strength ratio than other metallic alloys. Apart from their inherent properties, aluminum alloys like other metallic alloys show a significant change in their mechanical properties according to the machining parameters. The research literature on obtaining optimum mechanical properties of aluminum alloys that undergo machining is very limited. Moreover, the combined effect of several parameters on the machinability of aluminum alloys has not yet been explored. In this paper, the effect of three machining parameters (Depth of Cut (DoC)), feed rate (FR), and cutting speed (CS) on the subsurface damage and fatigue life of aerospace-grade aluminum alloy (Al-6082-T6) is observed. Samples are prepared using a full fractional approach to effectively capture the effect of all input parameters. Thereafter, samples were subjected to surface roughness, micro-hardness, and fatigue life tests. Results of surface roughness and micro-hardness tests are compared with fatigue life. The general linear model was employed to capture the percentage effect of each input parameter on the output parameters. The results showed that DoC was the main contributing factor that caused subsurface damage, while surface roughness and fatigue life were mainly affected by FR and CS. Optical microscope images showed a white layer formation that had higher hardness than the base metal. Overall, this research work proposes the input parameters that can be used to achieve minimum surface damage and fatigue life.

Winds are vital energy resources among various offshore renewables. The deep draft circular OC3 (Offshore Code Comparison Collaboration) spar-type hull supporting floating wind turbines has recently been installed worldwide. This study considers an OC3 5MW wind turbine with a tower base diameter of 6.5m and height of 77.6m, supported by circular and elliptical shapes for the dynamic analysis, using ANSYS–AQWA. The present study investigated the dynamic characteristics of the elliptical hulls with aspect ratios of 1, 1.5, 2, and 2.5 under the 50-year return periods of combined action of current, wave and wind for the Arabian Sea and the North Sea region. The model results depict that the dynamic responses in active degrees of freedom decrease with an increase in the aspect ratio of the hull and a minimum response is observed for the aspect ratio of 2. Further, the mooring lines fatigue life was estimated for both the sea states.

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.

An accelerated life testing procedure can reduce the lifetime of a material by observing the material's behavior under higher levels of stress than what is normally encountered. Useful inference hinges on the selection of an appropriate lifetime distribution and the substitution of an acceleration model for a distribution parameter, such as the mean or scale. The (inverse) power-law model is one such acceleration model that has applications to fatigue studies in metals, where failure tends to be crack-induced. The Birnbaum–Saunders distribution was developed to model fatigue in materials where the failure of a specimen is due to the propagation of a dominant crack. This paper will compare two Birnbaum–Saunders type models from the literature (that have power-law accelerated features) with a new but distinctive model proposed here. The new model is an accelerated life model for a reparameterization of the baseline distribution. Comparison of the three models will be via the aluminum coupon data set from Birnbaum and Saunders⁵ and issues of accelerated testing will be discussed.

Rolling Contact Fatigue (RCF) is a major cause of rail failure leading to replacement of rails. RCF defects are caused by a combination of high normal and tangential stresses between the wheel and rail. In this study, a methodology has been proposed to evaluate P-F (Potential failure-functional failure) interval of RCF defects based on RCF defect rate distribution and fatigue design life distribution. For estimating fatigue design life distribution, load under variable amplitude has been considered which is a case in the mixed traffic scenario. Stochastic S-N curve has been considered to account for probabilistic nature of fatigue life. The stress history can be calculated from the actual load history. RCF defect distribution can be estimated from the probability density function of the defects from the actual field data. The proper estimation of P-F interval will help the infrastructure managers to define rail inspection interval scientifically.

The variations of fatigue limit and fatigue life of a plain specimen of annealed and normalized 0.83% carbon steel were investigated. This material is used for cutting tools and the original microstructure includes a spherical microstructure. After heat treatment under some conditions, the microstructure changed to a lamellar microstructure. However, the fatigue lives of the plain specimens of this material showed almost the same tendency even after heat treatment under some conditions. In those cases, the initial crack length in the fatigue process is related to the size of the crystal structure and related to the distribution of ferrite. In the present study, the relationship between the distribution of hardness and the fatigue limit was investigated. Also, it was discussed that the fatigue limit of heat-treated 0.83% carbon steel could be evaluated by a relationship in which the parameters are the hardness and initial crack length. Finally, the tendencies of fatigue life of heat-treated 0.83% carbon steel were discussed based on the observations of crack growth behavior.

As the phenomenon of fatigue damage is a common failure mode of equipment, the reliability evaluation and life prediction have become a hot-spot. The precise prediction of fatigue life in the initiation stage has become necessary. The common prediction study for structural fatigue life takes less influence factors into consideration. The common prediction results of fatigue life cannot be quantitatively corrected by the influence factors at the same time. This paper presents a research on the prediction approach for structural fatigue life based on the multi-factor correction. The influence of some factors on the fatigue life was analyzed and the prediction approach for structural fatigue life based on multi-factor correction was raised. Then the fatigue life of axle housing was predicted by using the corrected approach, as the case study. Moreover, the result predicted by the local stress–strain approach and the experimental data were used to verify the accuracy of the corrected approach. It can be clearly demonstrated by the results that the corrected prediction approach can be used to achieve the precision fatigue life for engineering structures. Further, it is also a prediction approach endowed with engineering application prospects.

The girth welds of the steel connections in subsea pipelines are subjected to combined fatigue loading and static tensile loading in most of their service life. In this paper, both experimental and numerical studies are presented on the fatigue behavior of Carbon Fiber Reinforced Polymer (CFRP) composites repaired steel connections under combined loads. In the experimental program, each specimen is designed to be formed by two steel plates joined together by single-sided girth welds as a simplification of subsea pipelines, and reinforced by CFRP sheets on one side. The applied loads include a constant amplitude tensile cyclic load combined with a tensile static load, which is perpendicular to the cyclic load. The experimental results reveal that the superimposition of the tensile static load leads to a prolonged fatigue life. The effect gets more noticeable with increased tensile load. To further this study, an analytical model is developed on the basis of the Linear Elastic Fracture Mechanics (LEFM) method. It can be used to predict the fatigue lives efficiently. The comparisons with experimental results reveal that the analytical method is able to reasonably predict the fatigue crack growth life. Parametric studies are therefore performed using the proposed analytical model. The influence of CFRP layers, stress range and tensile static stress on the fatigue life was evaluated.

This study presents two hybrid methods, the full combination method and the simplified expression, for evaluating the fatigue life of linear structures with uncertain-but-bounded parameters subjected to stochastic excitations. First, approximate expressions of the spectral moments and spectral bandwidth parameters are derived based on the improved interval analysis via extra unitary interval and the interval Taylor expansion. Then, the lower and upper bounds of the interval expected fatigue damage rate and fatigue life are evaluated by fully or properly combining the two bounds of the spectral moments and spectral bandwidth parameters by the Tovo–Benasciutti method. Through the numerical study, the full combination method is recommended for the accurate assessment of the interval fatigue life, and the simplified expression is recommended for rapid evaluation of the two bounds of the interval fatigue life using the explicit expression. Finally, three numerical examples are adopted to illustrate the accuracy and efficiency of the proposed methods via comparison of the present results with the exact ones.

This paper presents an investigation of the possibility of improving the fatigue properties of an epoxy resin through dispersion of modified layered silicates within the polymer matrix. Montmorillonite-epoxy nancocomposites were successfully synthesized with a commercially available 1-Methylimidazole curing agent. The morphology of these materials was investigated by XRD and TEM. The findings demonstrated a pattern of clay morphology typically found in nanocomposite systems. Four point loading measurements showed an increase in modulus for 2.5 wt% and 10 wt% clay contents when compared to the unfilled epoxy, whereas the moduli showed a decrease for 5 wt% and 7.5 wt% clay contents. This behavior is typical for most particulate-filled systems. Fracture surfaces were examined using an E-SEM. The failure mechanism of the nanocomposites varied from that of the unfilled epoxy. Below a critical strain amplitude, the fatigue life of the filled epoxy improved significantly compared to that of the unfilled epoxy. In conclusions, the addition of silicates changes the fatigue failure mechanism and improves significantly the fatigue life.

For the distribution prediction of fatigue life and residual strength of fiber reinforced polymer composites, the existing models have the disadvantages of imprecision, instability and single applicability. A novel S–N curve model and a residual strength degradation model were first developed, which are independent and uncorrelated. After verifying their reliability, the statistical distribution models of fatigue life and residual strength were further derived and verified by using experimental data from literature. Compared with the other models, the proposed models can perfectly predict the probability distribution of fatigue life and residual strength under different materials, stacking sequences and stress levels, showing excellent prediction accuracy, stability and applicability.

This paper proposes a theoretical model for the description of tension-compression cyclic plasticity of gradient nanostructured (GNS) metals. The gradient grain size effect is considered by introducing the Hall–Petch relation for local yield stress and strain hardening. With the experimentally measured grain size distribution profile, the average axial stress can be calculated for cylindrical GNS metal specimens. The model was verified using experimental data obtained from 316L stainless steel treated by surface mechanical rolling treatment (SMRT). Moreover, the corresponding strain energy for cyclic plasticity can be calculated from the constitutive equations, providing an energy-based approach to explain the fatigue life of gradient 316L stainless steel.

A hybrid method was developed in this study for fatigue life prediction (FLP) of lead-free solder (LFS) joints in ball grid array package under the coupled electrical–thermal–mechanical (ETM) fields. A modified constitutive model for lead-free solder joints under coupled ETM fields was proposed to describe the mechanical and fatigue behavior of solder joints under coupled ETM fields. A modified damage model under coupled ETM fields was then developed to obtain the fatigue life of LFS joints under coupled ETM fields. Uniaxial tension tests of an Sn–3.0Ag–0.5Cu (SAC305) solders and coupled multifields fatigue experiments were performed to verify the accuracy, applicability and validity by the modified constitutive model and fatigue damage model under coupled ETM fields. Based on the modified constitutive model and fatigue damage model, a hybrid method, including current, temperature and mechanics parameters, was proposed for the FLP of the LFS joints, which was demonstrated to be able to predict the results well. A hybrid method provides an idea for investigating the fatigue life of lead-free solder joints in coupled fields.

Crack growth prediction of components subjected to spectrum loadings is an important issue in fatigue life assessment of industrial components. Effects of load interaction cause acceleration and/or retardation in fatigue crack growth rate. Disregarding of this phenomenon may lead to the nonconservative life prediction in some cases. In this paper two methods for load interaction consideration are used. The first model is Chang-Willenborg that is a modified Willenborg model and the second one is a new model based on the compressive residual stresses at the crack tip and original Willenborg model. In the development of the new model the required residual stresses at the crack tip are obtained from an elastic-plastic finite element analysis. Also the Original Rainflow Counting Method and Modified Rainflow Counting Method have been used to prepare the spectrum loading data. Using the above mentioned cycle counting methods and load interaction models, the crack growth of the plates are obtained for two different flight spectrum loading. Finally the results obtained from different methods are compared with those obtained from experiments presented by the others.

Burnishing is a chipless cold working finishing process, by which smooth and workhardened metallic surfaces can be produced. In this paper, an attempt has been made to study the effect of the number of tool passes on surface characteristics and fatigue life of cast Al-Cu components. The conducted experimental work shows, that improvements in surface roughness and fatigue life can be achieved by the application of this process. The increase in the surface hardness and the depth of workhardened subsurface layers of the considered cast alloy were also studied.

In this paper, a series of tests were carried out to study the fatigue property of dual phase steel and an improved fatigue model based on the change of microstructure of spot area and fatigue fracture mode was used to predict the fatigue life of dual phase steel. The effects of nugget diameter, sheet width, thickness to fatigue life of welding spot are discussed. The earlier fatigue crack appears always near the welding gap position due to the strong stress concentration here and the extension angle between fatigue crack and connection surface approximates 90°~110°. The academic data based on the prediction model is in accordance with actual test data which proves that the model mainly including equivalent stress strength factor of crack tip could reflect the fatigue fracture mechanism and fatigue property of steel exactly.

To solve the problem of a mining triaxial heavy-duty dump’s putting rod ruptures prematurely, When the dump in the bending and twisting conditions, the push rod’s static strength and stiffness was analysed by Hypermesh, and get the modals shapes and modal frequencies and generated a frame MNF file (modal neutral file) from the Ansys, established the rigid - flexible coupling model of the frame in ADAMS, get a load time history of fully loaded front and rear suspension. According to material fatigue properties’ S-N curve of the frame, using of MSC. Fatigue software the frame’s life was analyzed. The result showed the position of minimum fatigue life of frame is consistent to the position of abnormal rupture of putting rod in actual use; in order to improve the design of heavy-duty dump truck provides a reference.