Abstract Based on the fatigue life change of 300M landing gear steel due to overload during service, this study innovatively designed four overload modes according to the actual load spectrum of the landing gear. In this study, the application of overload continued until the specimen failed, and the effects of overload ratio, overload type and specimen thickness on the crack propagation behavior of 300M steel were compared and analyzed. The fatigue crack growth rate and fracture morphology of the specimens were characterized and analyzed, and the influence mechanism of the crack growth rate at each stage under different types of overload conditions and the influence of the thickness of the specimen on the overload delay effect were discussed.
The solidification cracking behavior in laser welds of steel/copper dissimilar metals was systematically investigated. T2 copper and SUS304 stainless steel were used in the study. The results showed that the occurrence of solidification cracking in welds was the synergistic effect of ε phase liquation, inclusions and composition segregation. During the welding process, the liquation of grain boundaries substantially reduced the cohesion between adjacent grains, as well as the resistance for intergranular crack propagation. The composition segregation inside the grains could induce lattice distortion, thus reducing the plastic deformation capacity of the material itself and concurrently increasing the susceptibility to cracks. In addition, an effective solution for inhibiting solidification cracking was proposed by using an oscillating laser, and the inhibition mechanism was further discussed. Laser oscillating welding significantly promoted grain refinement, solute diffusion and the formation of uniformly distributed ε-Cu precipitated phases in welds. It can improve the intergranular bonding, reduce the susceptibility to solidification cracking and increase the resistance to plastic deformation. The tensile strength of joints using laser oscillating welding is 251 MPa, 35.7% more than 185 MPa using laser welding. Meanwhile, the strain of joints using laser oscillating welding is 3.69, a 96% increase compared to 1.88 using laser welding.
Engineering components and structures in service are generally subjected to the multiaxial complex loads. The approach of critical plane has been widely accepted by most researchers as the best method in the multiaxial fatigue research field. It can be used well in the constant multiaxial fatigue loads, but not in the complex loads. Basis on analyzing characteristics of shear strain on material planes, the concept of weight-averaged maximum shear strain plane is proposed. A procedure is presented to determine the critical plane under multiaxial random loading. The angle values of the planes that experience peak values of maximum shear strains are averaged by employing the weight function, which is assumed to take into account the main factors of influencing the fatigue behavior, e.g. fatigue damage. The proposed algorithm is applied to the multiaxial in- and out-of-phase experiments to assess the correlation between the weight-averaged maximum shear strain direction and the position of the experimental fatigue crack initiation plane.
<div class="section abstract"><div class="htmlview paragraph">Lightweight design is a key factor in general engineering design practice, however, it often conflicts with fatigue durability. This paper presents a way for improving the effectiveness of fatigue performance dominated optimization, demonstrated through a case study on suspension brackets for heavy-duty vehicles. This case study is based on random load data collected from fatigue durability tests in proving grounds, and fatigue failures of the heavy-duty vehicle suspension brackets were observed and recorded during the tests. Multi-objective fatigue optimization was introduced by employing multiaxial time-domain fatigue analysis under random loads combined with the non-dominated sorting genetic algorithm II with archives. While evaluating fatigue life within optimization loops, particularly for multiaxial random load fatigue in the time domain, is time-intensive, this study is to improve computational efficiency in two strategies: 1) the dynamic adjustment of target nodes from the finite element model, using a weighted sum prior to performing fatigue damage prediction, 2) considering the actual cracking positions observed during the durability test, weld seams, identified as high-risk areas, were incorporated into the fatigue life prediction and optimization process. The fatigue evaluation results were in alignment with durability test outcomes of the suspension brackets, and the final optimization results were explored in both design and objective fields. The Pareto front was then utilized to show the trade-off between the conflicting objectives of lightweight design and enhanced fatigue performance to meet the enhanced durability requirements. This underscores the methodology's practicality and reliability in improving the durability and lightweight performance of suspension components.</div></div>
Several rotating rates and welding speeds were chosen to joint 6063/3A21 dissimilar aluminum alloys, tensile strength of the welds were measured to analyze effect of welding parameters on weld performance. Results show that tensile strength of the weld is better than the base material. Weld tensile strength will decrease under a too high or too low welding speed while effect of rotating rate on weld strength is relatively small. The weakest position is at heat affected zone at 3A21 side after T6 post weld heat treatment.
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