The adhesive behaviour of poly(p-phenylene benzobisthiazole) (PBT)/epoxy composites

Abstract

A modified scarf joint specimen was developed for characterizing the adhesive behaviour of poly (p-phenylene benzobisthiazole) (PBT) film/epoxy composites. This method subjected samples to varying amounts of normal stress (tensile or compressive) and shear stress. This resulted in the determination of two adhesive strengths; one in the absence of shear stress and one in the absence of normal stress. As a result, the dependence of the adhesive strength on the degree of normal stress was determined. The adhesive behaviour of PBT/epoxy composites was investigated at cure temperatures of 55, 85, 115 and 215°C. Adhesive strengths of 3.5 and 8.2 MPa were measured in the absence of shear and normal stress, respectively, for samples cured at 55° C. A decrease in adhesive strength with increasing cure temperature was attributed to residual cure and thermal stresses. The fracture of these composites was predominantly adhesive, resulting in a clean delamination of the PBT film from the epoxy surface. A modified Tsai-Wu failure criterion is suggested for these composites.