NDE for identification and evolution of impact damage in GFRP

Infrared thermography (IRT) was used to gain information, in real time and without destroying the material, about damage initiation and propagation in GFRP specimens, 2.90 mm thick, subjected to low velocity impact. A modified Charpy pendulum was used since it allowed for positioning of the infrared camera and viewing on-line the specimen surface opposite to the impact. Then, it was possible to record the impact phenomenon. The pendulum was modified to allow impacts on rectangular flat specimens, 130 x 100 mm, by a cylindrical steel impactor with a hemispherical nose. The specimens were loaded at different energy values by varying the height of the Charpy arm at the aim to investigate about the evolution of delamination and of other failure modes. The recorded thermal images were analysed by the ThermalCAM® ResearcherTM software. It was possible to investigate the different in plane damages by comparing the thermal mapping to the fixed energy level. Other important pieces of information were obtained from the temperature spectrum, which displayed in some cases a maximum peak in correspondence of fibre breakage. Each specimen was also inspected with lock-in thermography (LT); results are presented as phase images. Some specimens were also microscopically observed at the aim to validate the results.