A simplified model to predict the tensile and shear stress–strain behaviour of fibreglass/aluminium laminates

Abstract

Mechanical tests were carried out on a fibreglass/aluminium hybrid laminate, made of 0/90 S2-glass/epoxy laminae and Al 2024 T3 sheets, in order to find its tensile stress–tensile strain curve, residual tensile strain in correspondence of predetermined normal stress levels, and shear stress–shear strain curve. The basic layers were also suitably characterized, and a moderate anisotropy, reflecting the fabrication process, was found in the metal sheets. To theoretically predict the laminate response, classical lamination theory was modified to account for the inelastic behaviour of aluminium, which was substituted by an “equivalent” material governed by a simple constitutive law. Final failure conditions were calculated by assuming the maximum strain criterion and Tsai-Hill criterion for aluminium and fibreglass, respectively. Comparing the theoretical predictions with experimental results, it was concluded that the model adopted describes with sufficient accuracy the overall tensile stress–tensile strain curve, as well as the residual strains and the shear stress–shear strain response. The aluminium anisotropy influenced the tensile behaviour, markedly affecting the yield stress value, as also predicted by the analysis. Because of the complex phenomena occurring during final failure, the agreement between theory and data was only fair when the calculation of the tensile strength and failure strain was attempted. The material shear strength could not be determined, since the Iosipescu device used proven inadequate to result in material failure.