根据柔度变化原理,用自制“U”形位移规测量管材受内压时的裂纹咀张开位移,通过标定曲线比较即可得到裂纹沿深度方向的等效扩展量. According to the principle of variation of flexibility, the crack opening of the pipe under internal pressure was measured by the self-made “U” displacement gauge. By comparing the calibration curves, the equivalent expansion of the crack in the depth direction can be obtained.