Fatigue is one of the main causes of failures as well as mechanical fractures in structural details made of aluminium alloys under cyclic loading, where the materials (during the crack growth process) are subject to the stress R-ratio effects and crack closure phenomenon.

In this research work, a comparison of the effect of various crack closure/opening models on the fatigue crack growth behaviour of 6061-T651 aluminium alloy is presented. The crack closure models under consideration are the following: Elber; Katcher and Kaplan; Clerivet and Bathias; Schijve; Zhang; Newman; Savaidis; Codrington-Kotousov; and, Correia. A comparison between these models and experimental data is also done. Deterministic quadratic relations based on experimental results between $U$ vs $R$ and $R_{\mathit{eff}}$ vs. $R$ are suggested and compared with various crack closure models under consideration, where $U$ is a quantitative parameter function of crack opening and closing concept. This investigation into the crack closure/opening effects is made using experimental results from the first cycle and stabilised measurements ($U_1$ and $U_s$). Correia’s and Newman’s models presented a better agreement with the experimental results ($U_{d,s}$ or $R_{\mathit{eff},s}$). In this study, the crack closure quantitative parameters based on the first cycle and stabilised measurements reveal to be different, where $U$and $R_{\mathit{eff}}$ vary with the crack growth process, which suggests the assumptions listed by Hudak and Davidson, Ellyin, and Correia seem to be correct. Therefore, it can be concluded that the simultaneous monitoring of CTOD-based experimental measurements of the crack closure effects and getting the crack tip stress–strain field based on digital image correlation (DIC) measurements, supported by analytical/numerical solutions, seems to be a good way to describe the fatigue crack growth.

疲劳是铝合金结构细节在循环载荷下失效和机械断裂的主要原因之一，其中材料（在裂纹扩展过程中）受到应力 R 比效应和裂纹闭合现象的影响。

在这项研究工作中，比较了各种裂纹闭合/打开模型对 6061-T651 铝合金疲劳裂纹扩展行为的影响。正在考虑的裂缝闭合模型如下： Elber；凯彻和卡普兰；克莱维特和巴蒂亚斯；席夫；张; 新人; 萨瓦伊迪斯；科德林顿-科图索夫；还有，科雷亚。还对这些模型和实验数据进行了比较。基于实验结果的确定性二次关系$你$ 对比 $\mathrm{电阻}$ 和 ${\mathrm{电阻}}_{\mathit{效果}}$ 对比 $\mathrm{电阻}$ 建议并与正在考虑的各种裂缝闭合模型进行比较，其中 $你$是裂纹开闭概念的定量参数函数。对裂纹闭合/打开效应的研究是使用第一次循环和稳定测量的实验结果进行的（${你}_1$ 和 ${你}_{秒}$）。Correia 和 Newman 的模型与实验结果有更好的一致性（${你}_{d,秒}$ 要么 ${\mathrm{电阻}}_{\mathit{效果},秒}$）。在本研究中，基于第一次循环和稳定测量的裂缝闭合定量参数显示不同，其中$你$和 ${\mathrm{电阻}}_{\mathit{效果}}$随裂纹扩展过程而变化，这表明 Hudak 和 Davidson、Ellyin 和 Correia 列出的假设似乎是正确的。因此，可以得出结论，同时监测基于 CTOD 的裂纹闭合效应实验测量和基于数字图像相关 (DIC) 测量的裂纹尖端应力应变场，并得到解析/数值解的支持，似乎是一种描述疲劳裂纹扩展的好方法。