Damage detection at cryogenic temperatures in composites using piezoelectric wafer active sensors

An experimental evaluation of the structural health monitoring capability of piezoelectric wafer active sensors on composite structures at cryogenic temperatures is presented. The piezoelectric wafer active sensor-based electromechanical impedance and the pitch-catch methods were first qualified for cryogenic temperatures using piezoelectric wafer active sensor-instrumented composite specimens dipped in liquid N-2. Subsequently, damage detection experiments were performed on laboratory-scale composite specimens with (a) impact damage and (b) built-in Teflon patches simulating in service delaminations. Finally, a comprehensive damage detection test was performed on a full-scale specimen subjected to pressure and cryogenic temperature cycles. Based on these tests, we conclude that piezoelectric wafer active sensor-based structural health monitoring methods show promise for damage detection in composite materials even in extreme cryogenic conditions. Recommendations for further work are also included. Keywords