Evaluation of Stress Intensity Factor for Cylindrically Anisotropic Material under Mode I, II and III Loadings by Caustics Method

采用焦散线法测量了Ⅰ、Ⅱ、Ⅲ型载荷下的应力强度因子，并通过实验和数值模拟研究了这些载荷方式对测量精度的影响。在此基础上，提出了一种直接模拟焦散像的三维有限元数值方法。结果表明，本文所得到的最小初始曲线半径r_o^min取决于加载类型是Ⅰ型还是Ⅱ型。而在Ⅲ型加载下，无论初始曲线半径r_o如何变化，K的实测值与理论值基本一致。另一方面，采用焦散线法对正交各向异性日本扁柏材料在I型载荷作用下的变形进行了研究，并与三维有限元法的计算结果进行了比较。结果表明，当初始曲线半径r_o大于本文所得到的最小初始曲线半径r_o^min时，焦散线法对径向、切向和横向的KI都是有效的，模拟结果与实验图像基本一致。此外，三维应力场的大小与缺口尖端附近的离面位移之间存在密切的相关性。

The stress intensity factors under mode I, II and III loadings are measured by caustics method, and the effect of those loading modes on the measurement accuracy is experimentally and numerically examined. Furthermore, a numerical method based on the 3D finite element method (3D-FEM), which can directly simulate the caustic images, is proposed. As a result, it is found that the minimum initial curve radius r_o^min obtained in this study depends on the type of loading that is of mode I or mode II. In the case of modeIII loading, however, the measured value of K agrees with the theoretical one regardless of the change of the initial curve radius r_o. And the simulated results are in good agreement with the experimental images.On the other hand, the caustics method is examined for an orthotropic Japanese cypress material under mode I loading by using a coating technique, and the results are compared with those of 3D-FEM. As a result, it is found that the determination of K_I using caustics method is valid for radial, tangential and transverse direction, when the initial curve radius r_o is larger than the minimum initial curve radius r_o^min obtained by this study, and the simulated results are nearly in agreement with the experimental images. Furthermore, there was a close correlation between the size of 3D-stress field and out-of-plane displacement near the notch tip.