Towards a hybrid infrared approach for damage assessment

The thermoelastic response obtained from an infra-red (IR) detector contains twocomponents: the magnitude of the small stress induced temperature change caused by thethermoelastic effect and the phase angle of the temperature change relative to a reference signalgenerated by an application of a stress change. The phase angle is related to nonlinearity in thethermoelastic response and departures from the simple linear relationship that underpinsthermoelastic stress analysis (TSA). The phase data could be used to make an assessment oftemperature evolutions caused by viscoelastic behaviour resulting from damage and provide a basisfor its evaluation. In the current paper the physics of other infra-red techniques used for nondestructiveevaluation is used to better understand the nature of the thermoelastic response. Theobjective is to provide better exploitation of TSA by alternative processing of the IR measurements.Three case studies are presented that demonstrate the potential of the alternative processing forevaluating damage