The increasingly larger use of adhesive joints in the automotive industry demands a full comprehension of the adhesive behaviour when subjected to dynamic loadings. So far, some authors studied the effect of the strain rate regarding the adhesives performance, usually for the range of approximately 0–105/s; nevertheless, few studies are clear regarding the method used to calculate strain rate, especially when fracture mechanics analysis is the focus of study. Those who present approaches to assess the values of strain rate usually consider a constant value for each test. In this paper, a numerical approach is proposed to assess the strain rate in modes I and II in double cantilever beam and end notch flexure tests, respectively. The results of this study demonstrate that the strain rate in the adhesive bondline along the crack propagation in the double cantilever beam and end notch flexure tests is not constant when loaded at a constant cross-head speed. This finding also helps to justify why experimental R-curves of double cantilever beam tests, when loaded at speeds above quasi-static conditions, do not have a perfect plateau contrasting with those, usually presented by numerical simulations, that do not take into account the effect of the strain rate.

中文翻译：

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双悬臂梁和端部缺口弯曲试验中粘合剂层应变率的数值评估

汽车工业中越来越多地使用胶粘剂接头需要全面了解动态载荷下的胶粘剂行为。到目前为止，一些作者研究了应变速率对粘合剂性能的影响，通常在大约 0-105/s 的范围内；然而，关于用于计算应变率的方法的研究很少，特别是当断裂力学分析是研究的重点时。那些提出评估应变率值的方法的人通常会考虑每个测试的恒定值。在本文中，提出了一种数值方法来分别评估双悬臂梁和端部缺口弯曲试验中 I 和 II 模式的应变率。这项研究的结果表明，当以恒定的十字头速度加载时，在双悬臂梁和端部缺口弯曲试验中，沿着裂纹扩展的粘合剂胶层中的应变率不是恒定的。这一发现还有助于证明为什么双悬臂梁测试的实验 R 曲线在以高于准静态条件的速度加载时，与通常由数值模拟呈现的那些没有考虑到应变率的影响。