Evaluation of fracture toughness in composite structures using Infrared Thermography
Résumé
Fracture toughness is one of the most important properties of composite material for a lot of design applications involving damage and crack growth. Unfortunately, its value can be difficult to evaluate with standard methods such as the “compliance” method, for example in the case of cracks inducing small variations in specimen stiffness. In these special cases, the infrared thermography measure can permit to overcome the limitations of conventional methods. The first studied case, compressive fiber failure in unidirectional composite laminate has been chosen due to its difficulty to evaluate fracture toughness. Infrared thermography has been employed to follow compressive failure mode developing during an indentation test and a compression after impact test, and to evaluate the fracture toughness of compressive fiber failure. The obtained results show a good correspondence with the value found in a previous work on FE analysis of impact damage and are consistent with literature. Then an end notched flexure (ENF) test has been used to study the effect of growth stability on mode II interlaminar fracture toughness (FT) of a carbon/PEEK composite. The instability of the ENF test has been used to induce both stable and unstable crack growth with a static loading. Then two processes have been used to evaluate the FT; the standard process and the infrared thermography process. The both processes show similar conclusions and their complementarity allow to conclude GIIc varies between a low value for crack growth start or unstable propagation, and a high value for stable crack growth.