Micromechanical characterization of tensile strength of fiber composite materials

A micromechanical model is proposed to predict the tensile strength of unidirectional composite materials that have a fiber breakage. It is assumed that the load carried by the broken fiber is transferred eccentrically to the adjacent ones, which leads to a stress increase that would cause a reduction in the overall composite material tensile strength. The behavior of the model is investigated by a simulation approach using the SAP-90 computer program, where the composite material was simulated by two types of available elements in SAP-90. These elements are the FRAME element to represent the fibers as two-dimensional truss elements and the ASOLID element to represent the matrix as two-dimensional plane stress elements. Several combinations of fibers and matrices were used to perform the composite materials that have been used in this study, such as boron, graphite, Kevlar and glass fibers, and epoxy, polyamide, and polyester matrices. The results obtained from the proposed model are tabulated and plotted, and compared with those obtained from the SAP-90 computer program, which is found to work very reasonably. The influence of key parameters that are thought to effect the amount of reduction in tensile strength of composite materials due to fiber breakage has been considered in the model formulation. These parameters are specimen (lamina) length-to-width ratio, fiber volume fraction, applied tensile load, sheer modulus of the matrix, and elastic modulus of the fiber.