1Cr18Ni9Ti焊缝的物理疲劳短裂纹扩展实验

应用复型技术研究了1Cr18Ni9Ti管道焊缝金属的物理疲劳短裂纹行为。结果表明,依照“有效短裂纹准则”,在物理短裂纹（PSC）阶段,主导有效短裂纹（DESFC）扩展和有效短裂纹（ESFCs）的扩展及合并对疲劳损伤做出直接贡献,在DESFC裂尖前沿区域的ESFCs密度通过影响DESFC扩展,对疲劳损伤做出问接贡献。DESFC受到减弱的微观结构条件影响,逐渐演化为单条长裂纹扩展行为。ESFCs密度在微观结构短裂纹（MSC）阶段反映DESFC萌生区域、在PSC阶段反映其裂尖前沿的微观结构扩展条件,其统计演化特征与DESFC扩展率的统计演化特征一致。这说明了这一微观结构扩展条件的差异和演化,是随机疲劳性能与演化特性的本质原因。疲劳损伤是一个由初始混沌状态演化到MSC与PSC两阶段交界处独立无关的随机状态,然后到史相关随机状态的过程。

Experiment of Physical Short Fatigue Crack Propagation of 1Cr18Ni9Ti Weld Metal

An experimental research is made on the involving physical short fatigue crack propagation of 1Cr18Ni9Ti pipe-weld metal with a replicating technique. Based on the "effective short fatigue crack criterion"(Fatigue Fract. Eng. Mater. Struct., 1999, 22(6): 459-468), the result revealed that the propagation of dominant effective short fatigue crack (DESFC) and the propagation of effective short fatigue cracks (ESFCs), and their coalescence between ESFCs and DESFC contribute directly to the fatigue damage of material. The non-ESFCs in a form of the densities of ESFCs located ahead of the two tips of the DESFC contribute indirectly to the fatigue damage. In this physical short crack (PSC) regime, it exhibits a weakening micro-structural affecting with respect to a decrease of the densities of ESFCs, and thus the DESFC acts gradually as a long crack. Correspondingly, an agreement of involving statistical behaviour between the densities of ESFCs and the DESFC growth rates is observed. Thus, it is indicated that the difference of the involving micro-structural conditions for the DESFC initiation and growth between the sampling specimens is the intrinsic cause of the involving random fatigue properties. And the fatigue damage process is gradually from a initial chaotic state, to an independent random state at the transition of the micro-structural short crack regime and PSC, and then, to a historic dependent random state in PSC regime of fatigue damage.