Microdamage analysis of fibrous composite monolayers under tensile stress

Abstract

The quasi-static deformation and fracture modes of several types of fibrous composite materials are studied from a fundamental viewpoint using a new experimental approach. Microcomposite monolayers, consisting of single fibres accurately positioned into a thin poly-meric matrix, were manufactured using a specially developed technique, and tested for strength by means of a custom-made miniature tensile testing machine. The materials used were E-glass, and Kevlar 29, Kevlar 49 and Kevlar 149 para-aramid fibres, and a room-temperature curing epoxy resin. The tensile testing machine was fitted to the stage of a polarized light stereozoom microscope and the fracture process was recorded both via a standard 35 mm camera and a colour video camera. The fibre content of the first generation of micro-composite monolayers used in this work was low (<0.025) but definite effects on the modulus and strength were obtained as the experimental data followed the rule-of-mixtures quite accurately in most cases. The failure process was different in each type of composite and current statistical models for strength are unable to account for the modes of failure observed in some of the systems studied. The experimental approach proposed is potentially useful in the study of the effects of interface chemistry modifications, fibre-fibre interactions, matrix toughness modification, misalignment effects, and more, on the deformation and failure micromechanics of composites.