MOISTURE AND TEMPERATURE EFFECTS OF THE COMPRESSIVE FAILURE OF CFRP UNIDIRECTIONAL LAMINATES

Problems in measuring the compressive strength properties of continuou s fibre composites are still encountered at present day even though IS O and ASTM standards exist, and the strength prediction remains unreso lved topic. The objective of the present work is to evaluate the compr essive 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, max imum moisture contents and through-thickness diffusion coefficients of unidirectional laminates immersed in boiling water (accelerated agein g) are reported. Data are also presented on the effects of moisture an d temperature on the compressive strength and failure mode of these la minates. It is observed that failure of specimens tested in hot-wet co nditions 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 s tress-strain response and failure load of the composite; agreement bet ween theory and experiment is acceptable.