Modelling open hole compressive strength of composite laminates tested in hot wet conditions

The objective of this paper is to analytically predict the compressive and in-plane shear response of T800/924C carbon fibre epoxy composite laminates (currently available for aerospace structural applications) exposed to hot wet environments. The weight gains, maximum moisture contents and diffusion coefficients of unidirectional and various multidirectional laminates immersed in boiling water (accelerated aging) were measured in earlier work and briefly reported here. Data are also presented on the effects of moisture and temperature on the uniaxial compressive strength/failure mode of unidirectional laminates and multidirectional plates with an open hole. It is observed that the failure in the hot wet specimens always occurs as a result of out-of-plane microbuckling of the 0 degrees plies. This is attributed to the reduction in matrix strength properties and weakening of the ply interface arising from elevated temperatures and environmental conditioning. Test results are compared to theoretical predictions made by the Budiansky fibre microbuckling model and the Soutis-Fleck cohesive zone model for the open hole (notched) compressive (OHC) strength.