DEFORMATION AND DAMAGE MECHANISMS IN FIBER-REINFORCED ALUMINUM-ALLOY COMPOSITES UNDER TENSION

A well-consolidated composite consisting of aluminium alloy reinforced with continuous alumina-based fibres has been made by liquid metal in filtration and its mechanical behaviour investigated by destructive an d non-destructive means. The methods involve monotonic and unload/relo ad tensile testing, and include acoustic emission and slip-line studie s to monitor deformation. The longitudinal composite subjected to tens ile stress showed three-stage stress-strain behaviour. Stages I and II were linear and associated with elastic and plastic deformation of th e matrix, respectively, whilst stage III was related to fibre damage. With the transverse specimen, the stress-strain curve showed a linear stage I and a progressively decreasing slope in stage II as plastic de formation continued, but no well-defined stage I/II transition: some d egree of damage was again associated with fibre breakage. Differences of yield stress in directions parallel and perpendicular to fibres wer e attributed to residual stress in the matrix produced during manufact ure of the composite. Heat treatment increased the yield stress of the composites but the heat-treatment potential of the matrix alloy was n ot fully realized because of increased brittleness of the age-hardened matrix. (C) 1997 Published by Elsevier Science Limited.