基于剪切散斑干涉无损探伤的缺陷深度测量

Defect depth measurement based on shearography non-destructive testing

基于激光剪切散斑干涉技术构建了无损检测系统,通过对铝合金平板钻圆形盲孔覆橡胶层的方式制备了设有不同尺寸和深度的内部缺陷的复合材料粘接试件,利用施加负压激励研究了不同负压值下试件内部缺陷所在表面的散斑条纹和离面位移情况,并结合有限元计算验证了检测系统有效性。结果表明:相同缺陷深度和负压值下,缺陷尺寸越大,散斑条纹级数越多、离面位移越大;相同缺陷尺寸和负压值下,缺陷深度越深,散斑条纹级数越小、离面位移越小。在利用该剪切散斑干涉无损检测系统准确获取内部缺陷的形状、位置和尺寸等信息的基础上,进一步基于弹性薄板理论推导了缺陷深度。缺陷深度测量精度随缺陷尺寸增大而提高,同时随深度增大而降低,直径为20 mm深度小于1 mm的圆形缺陷深度测量误差值小于10%。本文研究为复合材料粘接结构内部缺陷的深度检测提供了有效途径。

In this paper, a non-destructive testing system is constructed based on laser shearography. By drilling circular blind holes and covering a rubber layer on an aluminum alloy plate, composite bonded specimens with internal defects of different sizes and depths are fabricated. By applying negative pressure excitation, the speckle fringe and out-of-plane displacement on the surface of the internal defects of the specimen were studied under different negative pressure values. Meanwhile, the finite element calculation is carried out to verify the effectiveness of the non-destructive testing system. The results show that the larger the defect size, the greater the order of the speckle fringe and the greater the out-of-plane displacement from the surface for the same defect depth and negative pressure;the deeper the defect depth, the smaller the order of the speckle fringe and the smaller the displacement from the surface at the same defect size and negative pressure value. After obtaining the accurate acquisition of information on the shape, position, and size of internal defects by the non-destructive testing system, the defect depth is further deduced based on the elastic thin plate theory. The accuracy of defect depth measurement increases with the size of the defect, and decreases with the depth of a circular interior defect with a diameter of 20 mm and a depth of less than 1 mm. This study provides an effective way to detect internal defect depth in composite material bonding structures.