基于采样云纹法的 TC4 合金疲劳微裂纹萌生机理

In order to investigate the microcrack generation mechanism of Ti-6Al-4V alloy material for aero-engine，the microscale displacement and strain distributions of a Ti-6Al-4V alloy before and after microcrack initiation were measured in a tensile-tensile fatigue test using the sampling Moiré method and local phase unwrapping algorithm. The positive and shear strain distribution characteristics of the microcracks near the notch before and after the initiation were measured and analyzed by the alloy surface micro-scale grid images taken with scanning electron microscope. And the microcrack occurrence process was specifically analyzed using strain distributions in conjunction with the images. The obtained results showed that the microcrack initiation on the specimen was not caused by tensile strain concentration，but by shear strain concentration. It indicated that the type of microcrack involved during crack initiation was a Mode Ⅱ crack，namely，a slip-type crack. The sampling Moiré method with the local phase unwrapping algorithm can effectively measure the strain distributions even in the presence of irregular cracks or large stains on the specimen surface.