A fully-coupled damage modelling of hygrothermally aged CFRP open-hole laminate under quasi-static tensile loading

Carbon fibre reinforced polymers (CFRP) have a wide range of applications in aeronautical, aerospace and civil engineering, while their mechanical performance can be degraded when exposed to hygrothermal environments. To evaluate the degradation in mechanical properties of CFRP laminates with different ageing degrees, a damage model fully-coupled with heat and moisture ingress is developed in this paper. Gravimetric test was first carried out on CFRP openhole laminate immersed in deionised water at 60 degrees C to obtain the moisture absorption parameters, i.e. moisture absorption rate, saturated moisture content, hygroscopic expansion coefficient. Meanwhile, the basic mechanical properties of dry and saturated CFRP were measured, including tensile modulus/strength, shear modulus/strength. The relationships between water uptake and mechanical properties were thus determined. FE modelling was carried out to simulate the moisture diffusion in CFPR laminate with different immersion durations, and the internal moisture distributions signifying various ageing degrees were obtained. User subroutines were developed to incorporate the moisture-induced damage of CFRP into the Hashin failure model as well as hygroscopic swelling and thermal expansion. To validate the FE model, quasi-static tensile tests were carried out on CFRP open-hole laminates with different ageing durations in deionised water at 60 degrees C. Good agreement was achieved when comparing with the numerical results in terms of load-displacement curves, peak loads as well as the fracture mode in failure region around the open hole.