In this study, a set of programmed random factors with non-zero mean were designed. Then various stress levels (15, 18 and 22 KN) were multiple superimposed to factors to form one random loading block (RLB), the blocks were repeated to failure to investigate the synergistic damage of 316H ASS under low-cycle fatigue (LCF), high-cycle fatigue (HCF) and ratcheting effect. The lifetime of cyclic RLB tests decreased with the increase of block-mean stresses σmBlock (208、255 and 311.5 MPa). The normalized strain amplitudes indicate that when the σmBlock amplitude below the yield strength (208 and 255 MPa), a stable ratchet accumulation phase allows the specimens to exhibit cyclic hardening behavior. When σmBlock (311.5 MPa) exceeds the yield strength, the ratcheting strain increases significantly and the specimens exhibit cyclic softening behavior. Especially, the transgranular cleavage fracture, quasi-cleavage fracture and intergranular secondary cracks were identified when the failure of cyclic RLB tests were induced by LCF, HCF and ratcheting. With the increase of σmBlock amplitude, the decrease of LAGB proportion and the increase of dislocation density further reduce the fatigue resistance. In addition to dislocation motion, the α’-martensite phase transformation induced by ratcheting-fatigue has been further demonstrated as a mechanism for coordinated deformation. The percentage of stresses (within one block) that exceeds the diverge critical stress (375.6 MPa) of stacking faults (SFs) determines the α’-martensite nucleation mechanism.

中文翻译：

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循环随机加载块作用下 316H ASS 的棘轮疲劳行为及断裂机制


在本研究中，设计了一组具有非零均值的程序化随机因子。然后将不同应力水平 （15、18 和 22 KN） 与因子多重叠加形成一个随机加载块 （RLB），重复这些块直到失效，以研究 316H ASS 在低周疲劳 （LCF） 、高周疲劳 （HCF） 和棘轮效应下的协同损伤。循环 RLB 试验的寿命随着块均应力 σmBlock （208、255 和 311.5 MPa） 的增加而降低。归一化应变幅值表明，当 σmBlock 幅值低于屈服强度（208 和 255 MPa）时，稳定的棘轮累积阶段允许试样表现出循环硬化行为。当 σmBlock （311.5 MPa） 超过屈服强度时，棘轮应变显著增加，试样表现出循环软化行为。特别是，当 LCF、HCF 和棘轮作用诱导循环 RLB 测试失败时，鉴定出跨晶解理断裂、准解理断裂和晶间次生裂纹。随着 σmBlock 幅值的增加，LAGB 比例的减小和位错密度的增加进一步降低了抗疲劳性。除了位错运动外，棘轮疲劳诱导的 α'-马氏体相变也进一步证明了作为协调变形的机制。超过堆叠故障 （SF） 发散临界应力 （375.6 MPa） 的应力百分比（一个块内）决定了 α'-马氏体成核机制。