Aluminum alloy and its welded joint are widely used in high-speed trains, which are subjected to complex fatigue loadings in service. The fatigue failure mechanisms and influential factors for Base Metals (BMs) and Welding Metals (WMs) subjected to low cycle (dwell) fatigue (R = 0) and (very) high cycle fatigue (R = −1) loads were investigated. The development of cumulative strain in tension–tension low cycle (dwell) fatigue was attributed to “cyclic ratcheting effect”, which developed only when the applied maximum stress level is higher than the yield strength. In that condition, the cumulative strains continually developed and resulted in ductile fracture for BMs, but gradually converged to a finite value and resulted in fatigue fracture for WMs. Further, the dwell loading contributed to slowing down the development speed of cumulative strain and extending the fatigue life for BMs. Moreover, the welding processing reduced the (very) high cycle fatigue strengths and shortened the fatigue lives due to the introduction of welding defects, and a model replacing the nominal maximum stress by an equivalent one was proposed for modeling the impact of those defects on fatigue properties, which agrees with the S-N data.

中文翻译：

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高速列车铝合金及其焊接接头的疲劳失效机理及影响因素


铝合金及其焊接接头广泛应用于高速列车，高速列车在服役中承受复杂的疲劳载荷。研究了贱金属 （BMs） 和焊接金属 （WMs） 在低周（停留）疲劳 （R = 0） 和（非常）高周疲劳 （R = −1） 载荷下的疲劳失效机制和影响因素。张力-张力低周（停留）疲劳中累积应变的发展归因于“循环棘轮效应”，只有当施加的最大应力水平高于屈服强度时，才会产生这种效应。在这种情况下，累积应变不断发展并导致 BMs 发生韧性断裂，但逐渐收敛到有限值并导致 WMs 疲劳断裂。此外，保压载荷有助于减慢累积应变的发展速度并延长 BM 的疲劳寿命。此外，由于焊接缺陷的引入，焊接加工降低了（非常）高周疲劳强度并缩短了疲劳寿命，并提出了一个模型来代替标称最大应力，用于模拟这些缺陷对疲劳性能的影响，这与 S-N 数据一致。