Effect of IFSS on tensile strength of unidirectional fiber composites using 3D-FEM simulation

Abstract

A Monte-Carlo simulation model based on 3D-finite element analysis was developed to clarify the effect of interfacial shear strength (IFSS) on tensile strength of a unidirectional composite with fibers placed in a hexagonal array. The simulation model comprises fiber, matrix and interface elements; thereby, fiber breaks, matrix fractures and interfacial debondings during loading can be predicted individually. Tensile fracture processes and strengths of a boron/epoxy composite were simulated at various IFSSs. Results show that as IFSS decreases, stress concentration factors to intact fibers adjacent to a broken fiber element decrease because of occurrences of interfacial debonding. However, since interfacial debonding also reduces load carrying capacity in broken fibers, composite strength is reduced in all fiber volume fractions. On the other hand, a large IFSS causes many matrix fractures at once; therefore, it induces low composite strength. Thus, intermediate IFSSs increase tensile strength of the composite. This means that there must be an 'optimum' IFSS which induces the highest tensile strength of the composite. The optimum value shifts to a low value as fiber volume fraction increases. This occurs because the matrix around broken fiber elements becomes more apt to be broken easily in shear at a higher fiber volume fraction, therefore enhancing normal stress on intact fibers.