This study presents an investigation on the influence of loading rate and temperature on mode I interlaminar fracture toughness of unidirectional composite laminates. An analytical model was developed to describe the temperature- and loading rate-dependent fracture toughness, and a loading rate coefficient was defined to evaluate the rate dependency. Quasi-static and dynamic double cantilever beam (DCB) tests were conducted at various temperatures from −20 to 110 °C. A dual electromagnetic Hopkinson bar was employed to perform dynamic tests under loading rates of 15 and 24 m/s to achieve pure mode I delamination. The experimental results show that the fracture toughness exhibits an obvious positive loading rate sensitivity at all temperatures, whereas the loading rate coefficient shows two different trends with temperature indicating different loading rate dependency. Fractography observations reveal an obvious transition in the dominant failure mechanism at low temperatures from fiber/matrix interface debonding under quasi-static conditions to brittle fracture of matrix under dynamic conditions. However, both the quasi-static and dynamic delamination surfaces exhibit multiple failure modes at high temperatures. It is reasonable to deduce that the effect of temperature and loading rate can be attributed to the nature of matrix, the bonding between fiber and matrix.

中文翻译：

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评估不同温度下复合材料层合板 I 型分层的加载速率依赖性

本研究研究了加载速率和温度对单向复合材料层合板 I 型层间断裂韧性的影响。开发了一个分析模型来描述与温度和加载速率相关的断裂韧性，并定义加载速率系数来评估速率依赖性。在-20至110°C的不同温度下进行了准静态和动态双悬臂梁（DCB）测试。采用双电磁霍普金森杆在15和24 m/s的加载速率下进行动态测试，以实现纯I型分层。实验结果表明，断裂韧性在所有温度下都表现出明显的正加载速率敏感性，而加载速率系数随温度呈现出两种不同的趋势，表明不同的加载速率依赖性。断口观察表明，低温下的主要失效机制从准静态条件下的纤维/基体界面脱粘到动态条件下基体的脆性断裂发生了明显的转变。然而，准静态和动态分层表面在高温下都表现出多种失效模式。可以合理推断，温度和加载速率的影响可归因于基体的性质、纤维与基体之间的结合。