在做三点弯曲疲劳裂纹扩张速率试验时,我们曾采用划线法,喷镀金属膜栅法、显微镜法和电阻法等不同的方法来测量试样裂纹的长度。前三种方法,尤其显微镜法,有操作简便,易行直观等长处,但只能测定试样的表面裂纹长度,不能测定其平均值,而且不能连续测量。国外有的用超声波探测仪来测量裂纹长度,此方法装置较复杂,灵敏度大约0.25毫米, In the three-point bending fatigue crack growth rate test, we have used scribing method, metallization coating method, microscopy and resistance method to measure the length of the cracked specimen. The first three methods, especially the microscope method, are easy to operate and easy to operate. However, they can only measure the surface crack length of the sample, can not measure the average value, and can not be continuously measured. Some foreign measurement of crack length with an ultrasonic probe, the method of the device is more complex, the sensitivity of about 0.25 mm,