abstract The fracture toughness of an adhesively bonded carbon fiber reinforced plastic joint under mixed mode (I and II) conditions was determined by means of the Fernlund–Spelt type double cantilever beam (DCB) test, where a rubber-modified epoxy adhesive was used. The R curves were determined by calculating the energy release rates, G I and GII, based on the beam theory, along with a finite element analysis. The total energy release rate GT (= GI + GII) strongly depended on the I–II mixed mode. This means that it remarkably increased with increasing mode-II component; furthermore, it varied with crack growth from G T C (at the onset of cracking) to G T S (at the steady crack-propagation region). The difference between G T C and G T S increased with the increase in the mode II component. Such R-curve characteristics were discussed based on observation of the fracture surfaces with a scanning electron microscope and the corresponding crack propagation-path behavior.

中文翻译：

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混合模态下高增韧环氧树脂胶粘复合材料接头的R曲线行为

摘要 通过 Fernlund-Spelt 型双悬臂梁 (DCB) 试验确定了在混合模式（I 和 II）条件下粘合粘合的碳纤维增强塑料接头的断裂韧性，其中使用了橡胶改性环氧树脂粘合剂。R 曲线是通过计算能量释放率、GI 和 GII、基于梁理论以及有限元分析来确定的。总能量释放率 GT (= GI + GII) 强烈依赖于 I-II 混合模式。这意味着它随着模式II成分的增加而显着增加; 此外，它随着从 GTC（开裂开始时）到 GTS（在稳定裂纹扩展区域）的裂纹扩展而变化。GTC 和 GTS 之间的差异随着模式 II 分量的增加而增加。