Impact damage detection on composites using optical NDT techniques

The paper presents the work that was carried out in the detection and, beyond of what is obviously visible to the naked eye, the extent of impact damage inflicted on composite panels designed and manufactured for structural applications in the aerospace industry. Using a drop-weight impact tester, the composite specimens were subjected to controlled impact conditions, ie relatively low velocity impact levels analogous to those expected from the drop of a heavy tool, collision with a bird etc. The composite specimens consisted of Monex core sandwiched between thin carbon/glass fibre reinforced plastic skins, typically identical to those used in the fabrication of unmanned air vehicles and helicopter rotor blades. The investigation attempted to establish the probability of detecting such barely visible impact damage with optical non-destructive testing methods such as digital shearography, electronic speckle pattern interferometry and infrared thermograph,. These NDT techniques were chosen to be employed in this study because they are non-contacting, whole-field, not limited to particular material types, provide fast and easy results in real time and have been proven reliable in a large number of applications in the laboratory/factory/field environment.