Detecting sub‐surface cracking in laminated membranes using infrared imaging

Abstract This paper presents a new experimental method that utilizes the thermoelastic effect to detect sub‐surface cracks in a laminated polymer membrane. A highly accurate infrared camera is used to measure the thermoelastic and dissipational heat signatures associated with bi‐axial fatigue loading of membranes. Changes in these thermal signatures arise whenever cracks form in any layer of the laminate, including fully embedded layers, thereby providing a novel method for experimentally measuring the initiation and growth of damage in sub‐surface layers. The proposed method is illustrated using a model 3‐layer system of EVOH sandwiched between two polyurethane layers. Bi‐axial fatigue loading was used to initiate cracking in the central EVOH layer without damaging the outer polyurethane layers. Cracking in the central layer resulted in a distinct thermal signature that was plainly visible using the proposed method.