The fracture toughness and slow crack growth (SCG) parameters of a quartz-based silica and a high-purity fused silica were measured as part of a program to review the reliability of the International Space Station windows. The materials exhibit the same fracture toughness (.75 MPa m^1/2 in N₂) and very similar SCG parameters. The literature on fused silica indicates excellent agreement of fracture toughness, but a very wide range of SCG parameters, even from the same institution, with strength-based methods usually yielding a lower power law exponent than direct crack velocity measurements. Use of the exponential function is shown to provide better agreement between test methods, with velocity curves derived from strength tests of bare fiber and polished or ground test specimens paralleling those from wide-range, direct crack velocity observations, implying that constant stress rate tests can predict long lifetime via the exponential function. However, much variation still exists. SCG parameters for soda–lime silicate are much less sensitive to the test method than fused silica. Static load tests and stress intensity measurements resulted in a fatigue threshold of .3 MPa m^1/2 for fused silica.

中文翻译：

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用于国际空间站窗玻璃的熔融石英的断裂力学性能

作为审查国际空间站窗户可靠性计划的一部分，测量了石英基二氧化硅和高纯度熔融石英的断裂韧性和慢速裂纹增长 (SCG) 参数。这些材料表现出相同的断裂韧性 (.75 MPa m ^1/2 in N ₂) 和非常相似的 SCG 参数。有关熔融石英的文献表明断裂韧性非常一致，但 SCG 参数的范围非常广泛，即使来自同一机构，基于强度的方法通常产生比直接裂纹速度测量更低的幂律指数。指数函数的使用被证明可以在测试方法之间提供更好的一致性，从裸纤维和抛光或研磨测试样本的强度测试中得出的速度曲线与从大范围直接裂纹速度观察得到的速度曲线平行，这意味着恒定应力率测试可以通过指数函数预测长寿命。但是，仍然存在很多差异。钠钙硅酸盐的 SCG 参数对测试方法的敏感性远低于熔融石英。^1/2用于熔融石英。