In this study, the effect of mixed-mode loading on fatigue crack growth under varying applied loads for SAPH440 material was experimentally investigated. Previous research has either examined the effect of mixed-mode loading at a fixed angle or its effect on slanted cracks. This paper uses a CTS specimen and a loading device to apply varying angles of load during Mode I loading conditions. Initially, a numerical analysis was performed to validate existing equations for the stress intensity factor, which quantifies the crack driving force in the experiments. In the crack initiation region, load shedding techniques and load increasing techniques were used to confirm fatigue cracking considering mixed-mode effects. The change in the threshold value according to the loading angle was also evaluated. In the crack propagation region, a multi-level loading technique was employed to assess the mixed-mode effects under varying loading angles. This process verified the mixed-mode effect under conditions where the applied load angle varies. The fatigue crack fracture surfaces were examined using digital camera capture and SEM. It was found that when mixed-mode loading occurs during Mode I loading, the fatigue crack propagation rate varies depending on the mixed-mode loading angle.

中文翻译：

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混合模式II对SAPH440材料疲劳裂纹扩展行为的影响


在本研究中，通过实验研究了 SAPH440 材料在不同外加载荷下混合模式载荷对疲劳裂纹扩展的影响。先前的研究要么检查了固定角度混合模式加载的影响，要么检查了其对倾斜裂纹的影响。本文使用 CTS 样本和加载装置在模式 I 加载条件下施加不同角度的载荷。最初，进行了数值分析以验证现有的应力强度因子方程，该方程量化了实验中的裂纹驱动力。在裂纹萌生区域，考虑混合模式效应，采用减载技术和载荷增加技术来确认疲劳裂纹。还评估了阈值根据加载角度的变化。在裂纹扩展区域，采用多级加载技术来评估不同加载角度下的混合模式效应。该过程验证了在施加的负载角变化的条件下的混合模式效应。使用数码相机捕获和 SEM 检查疲劳裂纹断裂表面。研究发现，当在 I 型加载期间发生混合模式加载时，疲劳裂纹扩展速率根据混合模式加载角度而变化。