Strain-rate dependence of the tensile fracture behaviour of woven-cloth reinforced polyamide composites

Tensile testing of plain-weave-cloth-reinforced polyamide composites has been carried out at various strain rates ranging from 1x10^-2 to 4x10¹ s^-1 in a servohydraulic testing apparatus. Four different polyamide composites studied were composed of two kinds of reinforcements, carbon fibre (CF) and glass fibre (GF), and two kinds of matrices, polyamide-6 (PA6) and modified polyamide-6 (mPA6). The experimental results showed that the tensile strength and failure strain of the composites tend to increase with increase in strain rate except in the case of GF/mPA6 whose fracture properties were stabilized at high rates (> 1x10⁰ s^-1). Damaged regions of the fractured specimens were observed in order to study the micromechanisms of tensile failure by means of polarized optical and scanning electron microscopes. The microscope studies showed that in the composites with the mPA6 matrix, extensive microcracking occurred in the matrix and transverse threads region prior to the final failure. The effects of strain-rate on the tensile fracture behaviour of these types of composite systems are discussed on the basis of these experimental results. (C) 2000 Elsevier Science Ltd. All rights reserved.