Photoelastic analysis of matrix stresses around a single fibre composite under dynamic loading

The strength of the fibre composites can be optimised by controlling the mechanism of failure. This paper studies the ability of automated polariscopes of view the stress distributions on the matrix around the single fibres. A set of samples previously tested in tension to a level of 10% strain were analysed statically using an automated phase-stepping polariscope. Photoelastic patterns for a reiong of 100um x 100 um around fibre breaks were analysed. The results of this analysis concurred with the theory that matrix failure in specimens with high adhesion between the fibre and the matrix to deform plastically. Failure of low fibre/matrix adhesion were caused by debonding of the fibre from the matrix. Dynamic loading at a strain rate of 0.25% min-1 was carried out on previously unloaded specimens using a dynamic automated polariscope. The system was found to work well, the main drawback in the analysis being scratches on the specimen surface causing noise in the analysis. This preliminary analysis was able to identify a fringe order peak around a fibre break showing the applicability of the technique for slow dynamic events with high magnification.