Tensile behaviour of multilayer thermoplastic composites

Abstract

Multilayer thermoplastic composite sheets consisting of alternating layers of two materials mainly differing in their ductility were laminated. The mechanical behaviour, irreversible deformation mechanism and fracture of two systems made up of (I) polystyrene (PS)/Noryl and (II) rigid PVC/PVC-EVA blend were studied. In System I the tensile properties change with composition up to 40 to 60 vol % PS while at higher PS content the latter dictates the behaviour of the system. Upon stretching, crazes and cracks were formed in the PS layer. Their propagation was retarded by the Noryl Layers. Subsequently the PS was deformed to rather high strains, otherwise not attainable, and shear bands, which were initiated at the crack tips, developed in the Noryl layers. The interaction between cracks and shear zones resulted in delocalized deformation and fracture delay. In System II the low strain properties linearly change with composition, identical to the behaviour of blends of similar compositions. However the ultimate elongation of three layers sheets and PVC/EVA blends attain maximum values which are higher than those of the components themselves, while that of five layer sheets changes gradually with composition. The good interlayer adhesion in all the systems studied enables cooperative irreversible deformation processes reflected by the mechanical behaviour and the fracture surface morphology of the composite sheets.