An evaluation of the scanning electron microscope mirror effect to study viscoelastically prestressed polymeric matrix composites

Abstract

A viscoelastically prestressed polymeric matrix composite (VPPMC) is produced by applying tensile creep to polymeric fibres, the creep load being removed before the fibres are moulded into a resin matrix. Following matrix curing, the viscoelastically strained fibres impart compressive stresses to the surrounding matrix, counterbalanced by residual tension in the fibres. VPPMCs based on nylon 6,6 fibres in polyester resin have previously demonstrated improvements in mechanical properties of up to 50% compared with control (unstressed) counterparts. Although the associated viscoelastic recovery forces are understood, little is known of the fibre-matrix interactions relating to prestress within VPPMCs. This is addressed by investigating composite samples with the scanning electron microscope mirror effect (SEMME). By comparing results from VPPMC samples with their control counterparts, the findings suggest that there are ∼30% fewer trapped negative charges in the former, implying that the VPPMCs possess higher fibre-matrix interfacial strengths. Tensile test results on similar composite samples support these findings. The effects of resin porosity in SEMME data are also evaluated and our findings suggest that porosity can significantly increase charge trapping.