Influence of Multiple Fiber Breaks on Stresses in a Fiber Composite With a Creeping Matrix

Abstract

Abstract In this work, the influence of pre-existing fiber breaks on the local creep response of a planar unidirectional fiber composite under steady axial tension is investigated. Shear deformation of the Newtonian viscous matrix material or interface is assumed to dominate the creep response and result in time and temperature induced fiber failures. The recently developed computational mechanics technique, called viscous break interaction (VBI), is used to compute the time-dependent stress and strain redistributions in the fibers and matrix in response to large numbers of transversely aligned and staggered fiber breaks. In VBI, the key influence function in response to one fiber break is built on shear-lag theory, and when employing weighted superposition concepts to this function, the stress fields around multiple breaks is then calculated. The results uncover distinctions in the stress redistribution between large numbers of aligned breaks, e. g. transverse cracks and a finite and infinite periodic row of short cracks, versus a large process zone of staggered (misaligned) breaks. The results also show how both the time growing interactions and spatial arrangement and size of several close breaks influence local matrix creep rate, fiber tensile stress redistribution, and macroscopically, the timescales of multiple creep stages in overall composite strain. In the present application of the VBI technique, the composite model is representative of polymer matrix composites and also ceramic composites with a viscous secondary phase at elevated temperatures. For these systems, the model assumes the reinforcement is the primary load bearing component with time-independent, elastic properties and has a much higher volume fraction than that of the matrix. These studies on the time evolution of local stress are important for modeling the statistical evolution of process zone or crack-tip failure mechanisms in time.