Subcritical crack growth can occur in a brittle material when the stress intensity factor is smaller than the fracture toughness if an oxidizing agent (such as water) is present at the crack tip. We present a novel bi-material beam specimen which can measure environmentally assisted crack growth rates. The specimen is “self-loaded” by residual stress and requires no external loading. Two materials with different coefficient of thermal expansion are diffusion bonded at high temperature. After cooling to room temperature a subcritical crack is driven by thermal residual stresses. A finite element model is used to design the specimen geometry in terms of material properties in order to achieve the desired crack tip driving force. The specimen is designed so that the crack driving force decreases as the crack extends, thus enabling the measurement of the crack velocity versus driving force relationship with a single test. The method is demonstrated by measuring slow crack growth data in soda lime silicate glass and validated by comparison to previously published data. The self-loaded nature of the specimen makes it ideal for measuring the very low crack velocities needed to predict brittle failure at long lifetimes.

中文翻译：

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用于测量环境辅助裂纹扩展的残余应力双材料梁试样

如果裂纹尖端存在氧化剂（例如水），则当应力强度因子小于断裂韧性时，脆性材料中可能会发生亚临界裂纹扩展。我们提出了一种新型双材料梁试样，可以测量环境辅助裂纹扩展速率。试样通过残余应力“自加载”，不需要外部加载。两种热膨胀系数不同的材料在高温下进行扩散结合。冷却至室温后，亚临界裂纹由热残余应力驱动。有限元模型用于根据材料特性设计试样几何形状，以实现所需的裂纹尖端驱动力。试样的设计使得裂纹驱动力随着裂纹的扩展而减小，从而能够通过单个测试测量裂纹速度与驱动力的关系。该方法通过测量钠钙硅酸盐玻璃中的缓慢裂纹扩展数据来证明，并通过与先前公布的数据进行比较来验证。试样的自加载特性使其非常适合测量预测长寿命脆性破坏所需的极低裂纹速度。