Infrared thermographic techniques for non-destructive damage characterization of carbon fibre reinforced polymers during tensile fatigue testing

A non-destructive fatigue damage characterization technique is needed in the scope of the development of new processing techniques for carbon fibre reinforced polymer (CFRP) composites. This study investigates two thermographic testing techniques with the aim of providing an in situ characterization technique of damage during fatigue testing of the mentioned CFRP specimens. A passive thermographic approach is used by measuring the temperature increase of the specimen due to hysteretic heating during fatigue testing. A concept for the determination of the mechanical loss factor (damping) from the temperature increase is presented. This loss factor serves a measure for the damage of the material. The second technique is an active approach where pulse thermography with photothermal heating is used for the characterization of damage via the heat conductivity in the thickness direction. Finally, a comparison with C-scan results is presented. It can be concluded that the infrared thermographic techniques show potential for the damage characterization in CFRPs during fatigue testing and they will be further investigated.