Moisture and Temperature Effects of the Compressive Failure of CFRP Unidirectional Laminates

Abstract

Problems in measuring the compressive strength properties of continuous fibre composites are still encountered at present day even though ISO and ASTM standards exist, and the strength prediction remains an unresolved topic. The objective of the present work is to evaluate the compressive response of the T800/924C carbon fibre-epoxy composite system (currently available for aerospace structural applications) in hot-wet environments using a modified Celanese test rig. The weight gains, maximum moisture contents and through-thickness diffusion coefficients of unidirectional laminates immersed in boiling water (accelerated ageing) are reported. Data are also presented on the effects of moisture and temperature on the compressive strength and failure mode of these laminates. It is observed that failure of specimens tested in hot-wet conditions always occurs as a result of out-of-plane fibre microbuckling. This is attributed to the reduction in matrix strength arising from elevated temperatures and environmental conditioning. In addition, two recent microbuckling models are employed to predict the compressive stress-strain response and failure load of the composite; agreement between theory and experiment is acceptable.