A STUDY OF THE STRESS-TRANSFER CHARACTERISTICS IN MODEL COMPOSITES ASA FUNCTION OF MATERIAL PROCESSING, FIBER SIZING AND TEMPERATURE OF THE ENVIRONMENT

The micromechanics of reinforcement of a model composite consisting of a high-modulus fibre embedded in epoxy resin has been investigated as a function of processing conditions, namely thermal stresses, fibre s izing, and temperature. The residual stresses on single-fibre coupons were monitored for both long- and short-fibre geometries with the tech nique of remote laser Raman microscopy (ReRaM). The systems studied co nsisted of sized and unsized fibre/epoxy systems at room temperature a s well as a sized system at 60 degrees C. Each composite was subjected to incremental tensile loading rip to full fragmentation, while the s tress in the fibre was monitored at each level of applied strain. The three systems exhibited differences in the residual stress field, with the unsized fibre being in compression. The average stress in the fib re increased linearly with applied matrix strain rip 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 ea ch fragment. Two different interfacial failure modes were identified, depending on the possible initiation of a mixed-mode matrix crack. At room temperature, the maximum interfacial shear str ess for both syste ms was of the order of 40 MPa with the sized system exhibiting slightl y better adhesion. Ar 60 degrees C, the sized system exhibited interfa cial shear stress values of the order of 20 MPa. (C) 1997 Elsevier Sci ence Limited.