Prediction of Interlaminar Shear Strength of Uni-Laminates Based on Fiber Bundle Composites

Abstract

Compare to unidirectional laminates, the preparation of fiber bundle composites is relatively simple. Previous studies have shown that fiber bundle composites and uni-laminates demonstrate similar failure features in the standard Iosipescu shear tests. But a considerable different strength value is observed between the two kinds of specimens. In this paper, three types of fiber bundle composites and uni-laminates were prepared using two kinds of carbon fibers and epoxy resins. The shear strength of fiber bundle composites and uni-laminates were compared to explore the underlying mechanisms resulting in the different shear strength. It is found through the analysis of the interfacial stress field between fiber bundle and matrix using the interface element method that the interfacial stress state in fiber bundle composite specimen is a coupling of tensile stress and shear stress, whereas the interface in unidirectional laminate specimen is in an ideal shear stress state. This difference makes the fiber bundle composites fail at a lower shear stress level. In this paper, a strength model was proposed to bridge the shear strength of fiber bundle composites and uni-laminates using Yamada-Sun strength theory. The experimental verification shows that the shear strengths of the uni-laminate predicted by the proposed model reach a good agreement with the measured values, with the relative deviation of that about 10%.