Etude theorique et experimentale du couplage thermoelastique dans les plaques composites

Abstract

Abstract This paper presents a theoretical and experimental study of composite laminates reinforced by continuous fibers of various orientations, subjected to a uniform increase of temperature. The theoretical part extends the classical laminate plate theory (CLPT) to thermoelasticity with anisotropic thermal expansion. A reference is made to the main existing results for the thermal expansion of balancedcross-plies. The ‘free-deformation’ equations for unblanced cross-plies are then derived. It is thus shown that a warping of the cross-ply is induced, due to a thermoelastic bending-membrane coupling. The experimental work was carried out on anti-symmetric cross-ply laminates, about which the theory predicts the existence of torsional coupling only KXY(KXX = KYY = 0) and one symmetric cross-ply. The test specimens were Boron-Aluminium composites with Vf's of 50% and 30%. For the specimens with a Vf of 50% the results from torsional testing are in good agreement with the theory. For the specimens with a Vf of 30%, at temperatures above 100°C the experimental results are much higher than the theoretical. The one symmetric specimen, contrary to theory, showed a lack of coupling only between room-temperature and a temperature varying from 40° to 80°C. The planar thermal expansion of symmetric and anti-symmetric cross-plies presents the same characteristics as that of unidirectionally reinforced composites: a linear region corresponding to the elastic deformation of the matrix, followed by a decrease in the coefficient of linear expansion which approaches that of boron fibres, corresponding to the plastic deformation of the matrix. Experimental results for the linear region are in good agreement with the theory. The effect of bending-membrane coupling on linear expansion is very small. Results in the plastic-deformation zone have been explained with the help of similar results on unidirectionally reinforced composites.