Papers by Keyword: Fatigue Life

Abstract: Offshore platforms are marine buildings commonly used for oil and gas exploitation activities. In general, reported failures in the life of offshore structures are fatigue failures resulting from environmental factors, such as random and continuous wave loads. In addition to environmental factors, the determination of the dimensions and thickness of the structure also plays an important role in increasing its strength. This study used Finite Element software with in-place analysis to calculate the strength and deterministic fatigue method for fatigue life analysis. This study aims to analyze the effect of the thickness of the jacket structure members on the strength and fatigue life. The results of the analysis showed that there was an increase in maximum UC and a decrease in fatigue life due to a reduction in thickness in the jacket members, where the initial model had a maximum UC of 0.64 with a fatigue life of 1285.83 years, while the 10% thickness reduction had a UC of 0.71 with a fatigue life of 552.07 years, a thickness reduction of 20% had a UC of 0.79 with a fatigue life of 213.80 years, a thickness reduction of 30% had a UC of 0.90 with a fatigue life of 62.14 years and a thickness reduction of 40% had a UC of 1.04 with a fatigue life 14.71 years. This research is expected to be a reference in designing the jacket structure to determine the optimal dimensions according to the planned fatigue life.

Abstract: This study aims to evaluate the fatigue life of the frame assembly, including the chassis frame and subframe, of a medium dump truck. The combined method of finite element (FE) analysis and multi-body dynamic (MBD) simulation is employed to analyze the structural stress. Road roughness, as the vibration excitation source in the vehicle MBD model, is simulated according to random road profiles of ISO 8608:2016, considering the vehicle speed. The stress-time histories are calculated using quasi-static analysis when the frame structure is subjected to dynamic loads. The fatigue analysis model in the crack initiation period is developed based on the P(%)-S-N curve and linear damage rule. The results indicate that the frame assembly meets the required fatigue strength, achieving an estimated service life greater than 20 years under combined operating mode. These outcomes provide valuable insights for the design and durability assessment of the frame structure when vehicles are utilized under different operating conditions.

Abstract: Fiber-reinforced composites are widely used in lightweight design for their exceptional specific strength. However, their inherent multiscale property variations require systematic consideration during structural optimization. This study develops a cross-scale analysis framework and fatigue life prediction model that explicitly accounts for the propagation of mechanical property variations from microscale constituent properties to macroscopic performance, utilizing representative volume element (RVE) modeling. Application of the framework to a carbon fiber composite battery box verifies its predictive capability, with results quantitatively revealing the mechanisms by which property variations affect structural durability. These findings establish a fundamental methodology for evaluating the operational performance of automotive composite structures.

Abstract: The FEM analysis evaluated how varying tightening loads affect diaphragm fatigue life at the position where fretting fatigue is most critical. Increasing body-side tightening load significantly shortened fatigue life, while increasing piece-side load slightly extended it. Under high body-side load, the beneficial effect of greater piece-side load became more noticeable. These findings indicate differing impacts from each side, with the body-side load having a stronger influence. An optimal tightening load balance may exist to maximize fatigue life.

Abstract: Unidirectional composite structures are increasingly utilized in structural design due to their excellent compressive strength. The present study provides an evaluation of the fatigue performance of materials commonly used in hip prostheses such as Ti-6Al-4V, Co-Cr alloys, UHMWPE, and a silicon matrix composite reinforced with unidirectional carbon fibers in three different fiber volume fractions. Using Bergmann's loading factors, stress calculations were conducted for an 80 kg individual. The Goodman criterion and S-N curves were applied to assess fatigue life. Results show the unidirectional composite with 70% fiber volume fraction has the highest fatigue resistance, making it most suitable for high-stress applications. In contrast, Ti-6Al-4V and Co-Cr alloys showed moderate performance, while UHMWPE was found to be suitable for low-stress applications. These results underscore the necessity of selecting the ideal composition to maximize durability and fatigue resistance in essential mechanical applications. This finding suggests a promising alternative for improving the design and performance of femoral neck implants. This suggests a promising alternative for improving the design and performance of femoral neck implants.

Abstract: The purpose of this study is to explore the effect of groove angle on the fatigue life of high-speed train brake discs. A thermal-mechanical coupling model of high-speed train brake discs with different angles (0°, 22.5°, 45°, 67.5°, and 90°) was designed and established. The effects of different groove angles on temperature and stress were studied and analyzed. Experimental specimens were prepared using special processing methods, and friction and wear characteristics experiments were carried out to further verify the simulation results. At the same time, based on the above results, life models of brake discs with different groove angles were established to study the effect of the angle on their fatigue life. Stress has a direct impact on the crack initiation life of groove brake discs, and temperature changes affect the material properties of brake discs, thereby affecting the crack initiation time. The crack growth life of 0° groove brake discs is longer, while the crack growth life of brake discs with other groove angles decreases as the groove angle decreases. Compared with the 0° groove angle, the crack propagation life of the 45° groove angle accounts for approximately 84.7%, while that of the 22.5° groove angle accounts for approximately 80.4%. These research results provide a theoretical basis and numerical research methods for the design of brake disc structures.

Abstract: This study was initiated to investigate the material characteristics of binder jet (BJ) manufactured austenitic stainless steel 316L, focusing specifically on the less studied bronze infiltrated version of this material. While BJ technology offers a compelling alternative to the current market leader laser powder bed fusion, all additive manufacturing methods are susceptible to porosity, which adversely affects the fatigue properties of parts, resulting in inferior fatigue life compared to traditionally manufactured counterparts. In this study, we explore the novel application of severe shot peening (SSP) as a post-processing method to enhance fatigue life. Through comprehensive microstructural analysis utilizing EBSD, mechanical properties testing via tensile testing, and fatigue life analysis using flexural bending fatigue testing, we demonstrate that SSP treatment induces surface modification, leading to increased material strength albeit with a trade-off in ductility. Moreover, our findings reveal a significant improvement in the fatigue life of the material. Utilizing SSP, we observed that the fatigue limit of the material more than doubled, surpassing the performance of the sheet metal counterpart of the same material. These results underscore the potential of SSP as an attractive method for property enhancement in additive manufacturing.

Abstract: Due to the recent increase in energy consumption, global environmental issues have attracted attentions in order to continue the sustainable development of society [1]. Currently, scrap-and-build becomes a mainstream in the field of constructions, which would use and /or dispose a large amount of materials. This situation results in massive energy consumption with a significant environmental impact [2]. Therefore, it is important to consider sustainable systems in the construction industry. In many countries, a lot of structures had been constructed during the period of rapid economic growth in the middle of the last century, and their constructions are reaching the end of their design lives. In particular, due to the significant increase in the number of automobiles, numerous cracks above the estimated numbers has been observed in the bridges of motorways. Therefore, the improvement of fatigue life is strongly required to keep a good condition of constructions for a long time. In addition, the nuclear power plant is one of important infrastructures in the modern society, and the proper maintenance of nuclear reactor has been required to ensure their safety after the accident at the Fukushima Daiichi Nuclear Power Plant caused by the Great East Japan Earthquake. Stress corrosion cracking is considered as the most important damage event in the maintenance of nuclear reactor. Stress corrosion cracking occurs, when three factors are combined: tensile residual stress due to welding, material sensitization in the heat-affected zone, and the corrosive environment. In other words, eliminating one of these factors might prevent from generating stress corrosion cracks, and it is expected to extend the fatigue life of nuclear reactors [3]. Therefore, shot peening has been conventionally used as a method to reduce fatigue cracks, because the compressive residual stress can be obtained by the surface’s deformation generated by the high-speed impact of shot grain. However, quantitative control of residual stress is not easy in the shot peening process. Because the shot peening treatment involves the combinations of many factors in the collision between shot grains and the specimen’s characteristics, and the mechanism of micro-structural transformation is also important point to consider the process’s effect. In addition, shot grains possibly remains on the specimen surface, and the contamination of shot grains might deteriorate the functionality of metal surface [4].

Abstract: The paper considers the issue of the influence of ambient temperature and service life on the endurance of pipe steels of underground pipelines. The results of numerous experimental studies allowed us to draw the following conclusions. An analysis of the experimental data indicates that for all the studied steels, the endurance decreases with decreasing air temperature, mainly down to-20... -30 °C. This can be explained by the embrittlement of the metal, i.e. a decrease in the plastic properties of the pipeline metal structure. In addition, it can be seen from the given data that low-alloy steels 48KhN, 09G2S, 10GS have the highest endurance. Weak endurance is mainly typical of grade 20 carbon steel. Experimental studies show that with an increase in the service life of pipes, their endurance decreases, and this tendency is inherent in all the studied steels. Studies of the endurance of pipe steels under complex stress states show that static torsional stresses close to the yield strength, when tested in the air, do not reduce fatigue life. Although the corrosive environment significantly reduces the cyclic strength of steel under shear stresses up to τ_cr=05τ_Y, the conditional limit of corrosion fatigue is not lower than when tested for corrosion fatigue under the action of only alternating stresses in a symmetrical cycle. It could be considered that the torsional stress in the pipeline system does not exceed 10 MPa. In that case, their influence on practical calculations on the endurance of pipes of underground pipeline systems can be neglected.

Abstract: This paper presented an experimental and numerical study of functionally graded materials made by the permanent casting method and in three models with different mixing ratios between aluminum and zinc alloys (FGM1, FGM2, and FGM3) as in figure 1. In the permanent casting process, three models of the functionally graded material were produced and mechanical tests were conducted on them such as tensile and hardness tests, and the behavior of tensile strength, yield strength, elastic modulus, and fatigue was analyzed on them. The fatigue test was conducted at six levels of load and at room temperature. Simulations were carried out for the three models and a simulated fatigue test for the functionally graded material into the Ansys program. The results of the fatigue test showed an apparent effect of the different mixing ratios of the functional-grade material. As well as the numerical results were, close to the experimental results. There was an improvement in the fatigue life compared to FGM3, by 23% to FGM2. In addition, the fatigue life of the FGM3 of 11% higher than from the FGM1 model. In addition to that, which is important, the improvement in the fatigue life characteristics of the third type was 36% compared to the alloys from which the functionally graded materials were made.