Fatigue crack growth in ductile materials is primarily driven by the interaction between damaging and shielding mechanisms. In the Paris regime, the predominant mechanism for retardation is plasticity-induced crack closure (PICC). However, some of the mechanisms behind this phenomenon are still unclear. Identifying and separating the three-dimensional aspect from other shielding aspects during experiments is extremely complex. In this paper, we analyze the crack opening kinematics based on local crack opening displacement measurements in both 2D high-resolution digital image correlation data and 3D finite element simulations. The results confirm that the crack opening stress intensity factor Kop differs along the crack path. we present a new method to determine Kop at the crack front allowing to identify PICC as the predominant shielding mechanism in fatigue crack growth experiments. Furthermore, this work contributes to the discussion on the damage-reducing effect of PICC, since we find that the influence on fatigue damage in the plastic zone remains negligible when the crack is closed and crack surface contact is directed towards the surface.

中文翻译：

---

AA2024-T3 疲劳裂纹生长过程中塑性诱导的裂纹闭合识别——基于高分辨率数字图像相关


延展性材料中的疲劳裂纹扩展主要是由损伤机制和屏蔽机制之间的相互作用驱动的。在 Paris 制度中，延迟的主要机制是塑性诱导的裂纹闭合 （PICC）。然而，这种现象背后的一些机制仍不清楚。在实验过程中，识别三维方面并将其与其他屏蔽方面分开是极其复杂的。在本文中，我们在 2D 高分辨率数字图像相关数据和 3D 有限元仿真中分析了基于局部裂缝张开位移测量的裂缝张开运动学。结果证实，裂纹张开应力强度因子 Kop 沿裂纹路径不同。我们提出了一种确定裂纹前沿 Kop 的新方法，允许将 PICC 确定为疲劳裂纹扩展实验中的主要屏蔽机制。此外，这项工作有助于讨论 PICC 的减损伤效果，因为我们发现当裂纹闭合且裂纹表面接触指向表面时，对塑性区疲劳损伤的影响仍然可以忽略不计。