The paper investigates mixed-mode fatigue crack growth in ductile polyurethane adhesives, emphasizing mode decoupling to distinguish the impact of each loading mode component on crack propagation. It also explores the temperature sensitivity of fatigue crack growth rates for each loading mode. Individual scrutiny of the role of each loading mode in tests is accompanied by an analysis of fatigue fracture surfaces to clarify failure mechanisms. The findings indicate differential sensitivity to ambient temperature between the mode I and mode II components in a mixed mode fatigue test. Notably, the fatigue response of the mode I component exhibited higher sensitivity to temperature than the mode II component in mixed mode fatigue fracture of the tested polyurethanes. The polyurethane adhesives' composition, particularly the hard segment ratio, emerged as a pivotal factor influencing their sensitivity to fatigue loading at elevated temperatures. Temperature effects led to a significant reduction (63%) in the mode I component of mixed mode fatigue for one of the tested adhesives, while the other exhibited a noteworthy increase (154%). This trend which was attributed to the hard segment ratio of the adhesives was also persisted in the shear mode of the mixed mode fatigue results.

中文翻译：

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高温下聚氨酯粘合剂的混合模式疲劳裂纹扩展和疲劳阈值分析

本文研究了延性聚氨酯粘合剂中的混合模式疲劳裂纹扩展，强调模式解耦以区分每种加载模式分量对裂纹扩展的影响。它还探讨了每种加载模式的疲劳裂纹扩展速率的温度敏感性。对测试中每种加载模式的作用进行单独审查，同时对疲劳断裂表面进行分析，以阐明失效机制。研究结果表明，在混合模式疲劳测试中，模式 I 和模式 II 组件对环境温度的敏感性存在差异。值得注意的是，在测试聚氨酯的混合模式疲劳断裂中，模式 I 组件的疲劳响应表现出比模式 II 组件更高的温度敏感性。聚氨酯粘合剂的成分，特别是硬链段比例，成为影响其在高温下对疲劳载荷敏感性的关键因素。温度效应导致其中一种测试粘合剂的混合模式疲劳的 I 型分量显着减少 (63%)，而另一种粘合剂则显着增加 (154%)。这种归因于粘合剂硬段比率的趋势在混合模式疲劳结果的剪切模式中也持续存在。