A progressive failure analysis model for composite structures in hygrothermal environments

A progressive failure analysis model involving hygrothermal effects is presented for predicting failure of composite structures in hygrothermal environments. The model introduces a constitution equation accounting for the hygrothermal strains. Synchronously, the temperature-induced modification of stiffness and strength parameters are involved in the stress analysis model, failure criterion and material degradation rules. A user defined subroutine was developed and embedded into a FEA package to perform the failure analysis of composite structures in hygrothermal environments. To verify the proposed model, specimens made of carbon/bismaleimide composites with two typical lay-ups were tested under tension and compression loadings, respectively, in which both dry and moisture specimens were tested at 25 °C, and only moisture specimens were tested at 75 °C and 105 °C. The good consistency between the numerical and experimental results, either the failure load or failure pattern, validates the proposed model. It follows that hygrothermal environments can hardly affect the tensile mechanical properties while significantly reduce the compressive behaviors of laminated composite structures. In addition, the failure mechanisms of typical tension and compression specimens are disclosed.