Fibre/matrix stress transfer through a discrete interphase, Part 1: single-fibre model composites

This paper reports a study of the effect of an interphase on strain develop ment in fibre-fragments. In order to form an interphase, an epoxy resin wit h known properties was applied to the surface of unsized reinforcing fibres and cured. These were then embedded in a matrix resin coupon, prior to fra gmentation testing. The study included an examination of the effect of inte rphase thickness, by applying multiple coats of one of the resins, and the effect of the interphase properties, by varying the coating resins. It was found that the average fragment lengths at saturation were difficult to dis tinguish. as a result of the scatter introduced by the statistical distribu tion of fibre strengths. However, the strain interval between onset of frag mentation and saturation was found to be more sensitive to variations in th e interphase properties. A finite element model was used to examine the strain development in the fr agments in more detail. The mechanical properties of the fibre, interphase and matrix were accurately incorporated into the model. providing a realist ic representation of the state of strain in the experimental samples. The p redicted deformations around the fibre-break provided an explanation for th e experimental observations. (C) 2001 Elsevier Science Ltd. All rights rese rved.