Effect of fibre sizing on the stress transfer efficiency in carbon/epoxy model composites

TLDR: In this paper, the micromechanics of reinforcement of a model composite consisting of continuous high-modulus fiber embedded in epoxy resin has been investigated as a function of fiber sizing.

Abstract: The micromechanics of reinforcement of a model composite consisting of continuous high-modulus fibre embedded in epoxy resin has been investigated as a function of fibre sizing. The composite was subjected to incremental tensile loading up to full fragmentation, while the stress in the fibre was monitored at each level of applied strain with the new technique of remote laser Raman microscopy. The two systems exhibited differences in the residual stress field with the unsized fibre being in compression. The average stress in the fibre increased linearly with applied matrix strain up to first fracture. After fracture, the stress in the fibre was found to build from the tips of the fibre breaks, reaching a maximum value at the middle of each fragment. The shape of the stress transfer profiles indicated minor differences between the two systems at moderate strains. At high strains, the stress transfer profiles of the two systems were distinctly different possibly owing to the presence of two different interfacial failure modes in the two types of model composites. The maximum interfacial shear stress for both systems was of the order of 40 MPa with the sized system exhibiting slightly better adhesion. SEM examination of the fracture surfaces revealed clear interfacial failure for the unsized system whereas the sized system indicated areas of good adhesion.