TEMPERATURE DEPENDENCE OF THE TENSILE STRENGTHS FOR THE SHORT GLASS FIBER-EPOXY COMPOSITE AND THE SHORT GLASS FIBER-UNSATURATED POLYESTER COMPOSITE

Abstract

The temperature dependence of the tensile strengths of epoxy resin and unsaturated polyester resin reinforced with random-planar orientation of short glass fibers was studied.In both composites, the tensile strength decrease with increase in temperature and the trend of decrease can be explained by the following formulae with the critical fiber length lc and the interfacial shear strength τ determined by means of our previous paper, where σcs, is the tensile strength of composite material reinforced with random-planar orientation of short fiber, L and d are the fiber length and the fiber diameter, respectively, σ and V are the tensile strength and the volume fraction, and subscript f and m presents fiber and matrix, respectively. Also σm′ is the stress of matrix on the fracture strain of composite material.Further the experimental values at the room temperature is smaller than the theoretical values and the difference can be explained by the thermal stress produced in molding owing to the large difference of thermal expansion coefficient between glass fiber and matrix resin.