Non-Destructive Testing of CFRP DCB Specimens Using Active Thermography

A Mode I Interlaminar Fracture Toughness test of carbon fiber-reinforced polymer laminates requires a double cantilever beam (DCB) specimen with a pre-implanted non-adhesive insert at the mid-plane to initiate delamination. However, the insert's quality and placement within the DCB specimen can be problematic, necessitating non-destructive testing methods. In this study, active thermography is employed to inspect potential defects around the Teflon insert in the DCB specimens. Both uniform and non-uniform heating methods have been applied, and thermal images were analyzed to obtain quantitative information, such as the insert's location and non-contact area. TSR-enhanced images were obtained using two variations in the classical thermographic signal reconstruction. The analyzed results confirmed the presence of non-contact areas in the DCB structures composed of both 22-layer and 24-layer CFRP prepregs. These areas may be attributed to residual air gaps formed during the hot-press molding of the DCB structures.