R Curves from Compliance and Optical Crack‐Length Measurements
R Curves from Compliance and Optical Crack‐Length Measurements
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柔度和光学裂纹长度测量的 R 曲线
DOI：
10.1111/j.1551-2916.2010.03758.x
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发表时间：
2010
期刊：
影响因子：
--
通讯作者：
J. Kruzic
中科院分区：
文献类型：
--
作者：
S. Fünfschilling;T. Fett;R. Oberacker;M. Hoffmann;H. Özcoban;H. Jelitto;G. Schneider;J. Kruzic
高韧性、高强度陶瓷，例如自增强 Si3N4，其卓越的机械性能源自促进 R 曲线急剧上升的微观结构。此外，准确评估裂纹扩展最早阶段的 R 曲线对于正确理解和预测机械行为是必要的。讨论了在加工凹口裂纹扩展的早期阶段，基于柔量和光学的方法来评估裂纹长度和 R 曲线。由于在初始裂纹扩展期间裂纹前沿的扩展不均匀，在通过光学观察测量裂纹长度时会错过裂纹扩展的最早阶段。评估所有裂纹扩展量的裂纹长度的最准确方法是通过求解方程组来分析柔度测量，该方程组结合了缺口的影响和桥接牵引力发展的顺应性变化。这种方法的计算成本很高，但对于 R 曲线急剧上升的材料，只需应用线弹性柔量评估（仅考虑缺口，而不考虑桥接牵引力）即可得到约 1% 以内的结果。当裂纹扩展较长时，这种近似方法会产生很大的误差；然而，在这个阶段，光学测量可以提供裂纹长度的准确评估，并能够准确评估 R 曲线。
High-toughness, high-strength ceramics, such as self-reinforced Si3N4, derive their superior mechanical properties from microstructures that promote very steeply rising R curves. Furthermore, accurately evaluating the R curve at the earliest stages of crack growth is necessary for correctly understanding, and predicting, the mechanical behavior. Compliance- and optical-based methods for evaluating the crack length, and R curve, at the early stages of crack extension from machined notches are discussed. The earliest stages of crack growth are missed during measurements of the crack length by optical observations due to the nonuniform extension of the crack front during initial crack extension. The most accurate method of evaluating the crack length over all amounts of crack extension is from compliance measurements analyzed by solving a system of equations that incorporates both the effects of the notch and the changes in compliance with the development of bridging tractions. Such a method is computationally expensive, but for materials with steeply rising R curves, simply applying the linear-elastic compliance evaluation, which only accounts for the notch, but not the bridging tractions, gives a result within about 1%. At longer crack extensions, such an approximation method will incur significant errors; however, at this stage, optical measurements can provide accurate assessments of crack length and enable an accurate assessment of the R curve.