Abstract The current study presents a novel test method to experimentally cancel out the thermal stresses in dissimilar material joints. For the commonly used double cantilever beam test the presence of thermal stresses results in a significant mode mixity at the crack tip, which varies with applied load even if the elastic properties of the adherends are similar. This is particularly a challenge for fibre reinforced plastics bonded to metals due to the large difference in thermal expansion coefficients. The presence of mode-II loading is likely to provide a higher fracture energy from experiments than if tested under pure mode-I loading, which can lead to non-conservative results when using standard test methods. To overcome this challenge a novel test method inspired by the mixed mode bending test is developed. It is shown that the thermal stresses can be cancelled by applying initial constant loads during testing, and that the fracture toughness under pure mode-I loading can be obtained under specific conditions. The test method is validated by carrying out virtual compliance calibration experiments using cohesive zone finite element modelling. As the test method relies solely on analytical calculations and can be used with standard test equipment, it is relatively simple to apply in practice.

中文翻译：

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具有热残余应力的异种材料接头 I 型断裂韧性的实验测量

摘要 当前的研究提出了一种新的测试方法，可以通过实验消除异种材料接头中的热应力。对于常用的双悬臂梁测试，热应力的存在会导致裂纹尖端的显着模式混合，即使被粘物的弹性特性相似，也会随着施加的载荷而变化。由于热膨胀系数的巨大差异，这对于与金属粘合的纤维增强塑料来说尤其具有挑战性。与在纯模式 I 加载下测试相比，模式 II 加载的存在可能会从实验中提供更高的断裂能量，这在使用标准测试方法时会导致非保守结果。为了克服这一挑战，开发了一种受混合模式弯曲测试启发的新型测试方法。结果表明，在测试过程中施加初始恒定载荷可以消除热应力，并且可以在特定条件下获得纯I型载荷下的断裂韧性。通过使用内聚区有限元建模进行虚拟柔度校准实验来验证测试方法。由于该测试方法完全依赖于分析计算，并且可以与标准测试设备一起使用，因此在实践中应用起来相对简单。