Estimation of delamination thickness in a multi-layered thermally thin structure by step heating thermography

The performance of a multi-layered structure is dependent upon its structural integrity. The main challenge posed to the structural integrity of such structures is the vulnerability of the interface to the formation of defects (like delamination, crack, void). Hence it becomes compelling to study such structures and propose methodologies that could detect and characterize the defects. This paper presents an approach to estimate the delamination thickness formed at the interface of a two-layered structure (a simple case of a multi-layered structure). An analytical expression of delamination thickness is derived using the electrical analogy approach. The saturation value of absolute thermal contrast, which is a characteristic feature of the thermal response of material or structure with defect under step heating has been used to derive the analytical expression of delamination thickness. The proposed approach is fast, simple, noncontact and devoid of extensive data handling. Simulations and experiments have been done to verify the approach. This approach can provide guidance during the design phase of multi-layered structures and aid in defining their failure threshold depending on the application. Additionally, it can also be implemented in manufacturing units during quality checks or can also be used for in situ defect characterization.