Thermoelastic characterisation of damage around a circular hole in a GRP component

This paper introduces a new infra-red detection system known as Deltatherm, which has the capability of collecting thermoelastic and thermal data virtually simultaneously. Full-field images from both types of measurement can be produced in as little as 1.2 seconds. An experimental programme is described that assesses the potential of using the Deltatherm system for damage monitoring and assessment. A unidirectional epoxy/GRP laminate test specimen with a central circular hole was studied. To confirm that the thermoelastic data was providing accurate stress data the thermoelastic output from the undamaged specimen was compared to that from a finite element model. The hole was then used as a damage initiator by applying a damaging cyclic load to the specimen. Thermoelastic and thermal images were taken throughout the fatigue cycle to monitor the damage evolution. Normalised thermoelastic images are presented from around the hole at various stages during the tests, and are accompanied by thermal images of the data taken from the same tests. The results show that considerable viscoelastic heating takes place as loading time increases and that the thermoelastic data is significantly affected by this increase in temperature.