The detection and imaging of internal defect using ESPI-based strain analysis

Abstract

Optical NDE (Nondestructive Evaluation) techniques such as ESPI (Electronic Speckle Pattern Interferometer) and shearography that are non-contact and real-time method are used to detect the defects in material. However, ESPI measurement is affected by disturbance such as rigid body motion, and has difficulty in recognizing the real shape and size of the defect, Shearography also involves several problems like it needs several operator-dependent factors including the amount of shearing and shearing direction for the quantitative analysis of internal defect, and it does not show the exact shape of the defect. In order to overcome these problems and evaluate the internal defect quantitatively in this study, the imaging of the inner defect based on the ESPI technique is proposed. In this method, the external perturbative load such as thermal load is induced to the specimen, and the deformation distribution of the specimen is measured by ESPI. Then the distribution of the shear strain energy is obtained by the strain analysis of the ESPI measurement result. On the edge of the defect, the shear strain energy is concentrated, so we can obtain the outline of the internal defect by following the peak point of the shear strain energy distribution. This method makes it possible to evaluate the size and shape of the defect quantitatively without operator-dependent factors.