Philippe Beguelin

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

Abstract Tensile testing of plain-weave-cloth-reinforced polyamide composites has been carried out at various strain rates ranging from 1×10−2 to 4×101 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 (>1×100 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.

Influence of the morphology on the impact fracture behaviour of iPP/EPR blends

Abstract An original approach is presented whose aim is to distinguish the contributions of the modified content and of morphological factors to the impact fracture resistance of three industrial rubber toughened isotatic polypropylenes (iPP/EPR). It consists of diluting the different iPP/EPR with neat iPP in order to bring them to the same modifier content without substantially altering the size and shape of the modifier inclusions. The role of the morphology is then assessed by comparing the fracture properties of the diluted materials. Results for the undiluted materials indicate that the material with the highest modifier content offered the best fracture resistance under impact conditions. As expected, the ductile-to-brittle transitions moved to lower speeds with decreasing temperature, but the ranking of the impact resistance of the blends remained unchanged. Results for the diluted materials showed that increasing the average modifier particle size and/or the PE content of the modifier resulted in a small decrease in toughness. However, the mechanical behaviour was concluded to be predominantly governed by the modifier content.