Sampling moiré (SM) method is one of the modern deformation measurement methods in photomechanics. This method realizes the visualization measurement of deformation field by a sparse sampling of grating images, showing the advantages of high efficiency and strong robustness. However, in the traditional sampling moiré method, the unidirectional sampling mode is used with the result that the two-dimensional deformation cannot be acquired at the same time. In this paper, by combining the orthogonal sampling and Fourier phase analysis techniques, an orthogonal sampling moiré (OSM) method is proposed with which the two-directional moiré phase of specimen grating can be separated synchronously. The accuracy of the OSM method for the deformation measurement is verified by numerical experiments and PMMA uniaxial tensile tests. As an application, in a scanning electron microscope (SEM), the deformation field near the crack tip of small fatigue cracks is measured, based on which the crack opening displacement (COD) and the stress intensity factors (K) are obtained. Furthermore, the crack closure effects at different temperatures are characterized. The experimental results show that the crack closure significantly affects the process of small crack growth at both room temperature and high temperature, and the crack opening load at high temperature is greater than that at room temperature, which indicates that small cracks are easier to close at high temperature.

采样莫尔（SM）法是现代光力学变形测量方法之一。该方法通过光栅图像的稀疏采样实现了形变场的可视化测量，具有效率高、鲁棒性强的优点。然而，传统的采样摩尔纹方法采用单向采样方式，无法同时获取二维变形。本文结合正交采样和傅里叶相位分析技术，提出了一种正交采样莫尔（OSM）方法，该方法可以同步分离样品光栅的双向莫尔相位。通过数值实验和 PMMA 单轴拉伸试验验证了 OSM 方法用于变形测量的准确性。作为应用程序，在扫描电子显微镜（SEM）上测量疲劳小裂纹裂纹尖端附近的变形场，据此得到裂纹张开位移（COD）和应力强度因子（K）。此外，还表征了不同温度下的裂纹闭合效果。实验结果表明，裂纹闭合对室温和高温下小裂纹的扩展过程都有显着影响，高温下的裂纹张开载荷大于室温，说明小裂纹在高温下更容易闭合。高温。表征了不同温度下的裂纹闭合效果。实验结果表明，裂纹闭合对室温和高温下小裂纹的扩展过程都有显着影响，高温下的裂纹张开载荷大于室温，说明小裂纹在高温下更容易闭合。高温。表征了不同温度下的裂纹闭合效果。实验结果表明，裂纹闭合对室温和高温下小裂纹的扩展过程都有显着影响，高温下的裂纹张开载荷大于室温，说明小裂纹在高温下更容易闭合。高温。