Effect of fiber positioning on mixed-mode fracture of interfacial debonding in composites

Abstract

Under transverse tensile loading, fibers oriented perpendicular to the tensile direction can undergo fiber/matrix debonding. Experiments show that the first stage of fiber/matrix interface debonding is mode-I dominated fracture with very fast crack growth rate. Subsequent stable crack propagation along the interface is due to mixed mode I/II fracture. The aim of this study is to explore ways to stabilize the early stage of debonding so that it becomes possible to determine the mixed mode interfacial fracture properties for the entire mode-mixity range by in-situ observations. Therefore, the objective of this study is to stabilize crack initiation in the dominant mode-I fracture by changing the position of one fiber with its neighboring fiber or hole using the finite element analysis. The progressive fiber/matrix debonding is studied by focusing on the interaction of one fiber with its neighboring fiber or hole. The results show that decrease of the position angle stabilize the crack growth at the interface in the ligaments. This effect is more significant in the cases with small ligament thickness. In the two-fiber model and at very small ligaments the results show that the crack growth stops when the crack tips meet each other in the ligament and further crack growth is under dominant mode-II fracture. In the fiber-hole model, both the crack initiation and propagation are stabilized by decrease of the position angles at very thin ligaments. This paper suggests to use two fibers instead of a single fiber in order to ease the characterization of interfacial properties.