STRAIN RATE AND TEMPERATURE DEPENDENCES OF INTERFACIAL YIELD SHEAR STRENGTH AND CRITICAL FIBER LENGTH FOR THE GLASS FIBER-THERMOSETTING RESIN COMPOSITES

Abstract

In the short glass fiber-thermosetting resin composites, the interfacial yield shear strength or critical fiber length is one of the dominating factors for the effect of reinforcement. In this paper, the strain rate and the temperature dependence of these factors were studied for the glass fiber-epoxy resin and glass fiber-unsaturated polyester resin composites.The interfacial yield shear strengths increase in proportion to the logarithm of the strain rate and the slope decreases slightly as the temperature increases. The strain rate and temperature dependences are more remarkable for the composites of which glass fiber surfaces are treated with silane coupling agent than ones of which fiber surfaces are treated with release agent. The strain rate and temperature dependences of interfacial yield shear strength τ_??_T can be related by the following equation.where _??_ is the strain rate, aT is the shift factor and subscript T represents the environmental temperature. K1 and K2 are corlstants depending on the system of composite, conditions at the fiber-matrix interface and the reference temperature. The strain rate-temperature reduction of mean critical fiber legth (_??_c)_??_, T cam be estimated with (lc) _??_, T=σt d/2τ_??_, T. using τ_??_, T given by the above equation. Here _??_l is the mean strength of links and d is the fiber diameter.