Investigation of self-heating and damage progression in woven carbon fibre composite materials,following the fibres direction,under static and cyclic loading

Abstract

Infrared thermography is commonly used as a non-destructive testing technique for damage monitoring of composite materials under mechanical loadings. Self-heating tests consist in monitoring the stabilized heating of a material submitted to cyclic loading for increasing values of stress level. It appears that the load threshold from which the thermal behaviour changes can be related to the fatigue limit of the tested material. In this paper, this stress threshold is compared to the heating of a woven thermoplastic composite material submitted to a monotonic tensile test. Indeed, during a quasi-static tensile test, the material temperature cools down, due to thermoelastic effect, before warming up again, due to both viscous effects and first damage evolutions. The comparison, which is made for the warp direction only, is also based on microscopic optical scanning of the specimen edge and passive acoustic monitoring. It is shown that thermal changes detected in the composite samples are associated with damage occurring under both static and cyclic loading, for similar stress levels. This result indicates that the static tests make it possible to estimate a damage threshold, therefore a potential fatigue limit, even faster than with self-heating tests, which opens very promising prospects as for the determination of the fatigue limit of woven composite materials reinforced by carbon fibre yarns.