Evaluation of Microscopic Damage Behavior in Discontinuous Fiber Reinforced Resin Composites

Abstract

In this study, three-point bending tests were performed for discontinuous glass fiber reinforced plastic composite material. Specimens with both unspread and spread fiber bundles were used. In specimens with unspread fiber bundles (unspread specimens), fiber bundles (fiber length is about 12mm) is randomly-oriented. In specimens with spread fiber bundles (spread specimens), fibers are spread (fiber length is 4-6 mm) and no fiber bundle is observed in the specimens. In order to investigate the difference in damage behavior in unspread and spread specimens, damage growth behavior was observed by an optical microscope and acoustic emission (AE) behavior was monitored during bending test. In the unspread specimens, the stress-deflection curves showed nonlinear behavior which is due to the initial crack formation in fiber bundles whose fiber direction is almost perpendicular to the tensile stress. The stress-deflection curves also shows the intermittent stress reductions which corresponds to the crack growth at the fiber bundle interfaces. In the spread specimens, the stress-deflection curves showed almost linear behavior which reflects the fact that few damage is observed until the maximum stress is reached. It was also found that the spread specimens showed higher strength than the unspread specimens. The results of AE monitoring were well correlated with the stress-deflection curves and the optical damage observation.