Defect Depth Characterization via Thermally and Pneumatically Induced Shearography for Nondestructive Component Inspection in the Automotive Sector

The following approach introduces a novel method for defect depth characterization using digital Shearography, which is a non-contact, full-field, and material-independent optical interferometric method that enables fast and nondestructive testing (NDT) of components, especially in industrial environments such as the automotive sector. While traditional techniques like computed-tomography, ultrasonic-testing, or thermography can offer depth approximations but they often involve high costs, longer testing times, or limited accessibility. In contrast, the method introduced utilizes various excitation methods in combination with shearographic evaluation to derive procedures for depth estimation of subsurface defects. Recent developments in Shearography have enhanced the method’s robustness and industrial applicability. By detecting the surface deformation behavior in the nanometer range under defined loading, depth-related characteristics of hidden defects can be extracted. Loading can be applied thermally, pneumatically, or mechanically. The proposed approach employs dedicated test specimens and a series of calibration measurements to derive a correlation for characterizing defect depth from the temporal progression of thermally induced surface deformation behavior. Pneumatic excitation, in particular the use of negative pressure loading, is also being explored as an alternative loading mechanism. By capturing image sequences during the deformation change between loading conditions of the specimen, this new approach enables both lateral and depth-resolved defect characterization. The method was experimentally validated on representative parts, demonstrating its practical relevance for industrial NDT use cases in which subsurface defect depth directly impacts structural integrity. Shearographic imaging has been well established for lateral defect estimation. The approach presented in this work extends this capability by enabling fast and cost-efficient characterization of defect depth, representing an important step toward more comprehensive three-dimensional defect evaluation.