Toughened carbon fiber/epoxy composites: the relative influence of an elastomer interphase and elastomer dispersed in the matrix

Abstract

A micromechanical model based on the three-phase method of cells is used to predict the effective properties and thermo-mechanical stresses in carbon fiber/epoxy composites that have been modified by the addition of elastomer. Three composite configurations are considered: (1) carbon fiber/epoxy without elastomer, (2) carbon fiber/epoxy containing an elastomer interphase between the fiber and the matrix and (3) carbon fiber/epoxy with elastomer dispersed in the bulk matrix. The variables investigated include the elastomer volume fraction, the elastomer placement and the fiber volume fraction. Results from the parametric study indicate that the composite response is significantly influenced by all three variables. Positive aspects are identified with respect to each elastomer configuration. In general, a thin, concentric elastomer interphase surrounding each fibril appears more beneficial to the reduction of tensile residual thermal stresses. However, elastomer dispersed in the matrix can also yield favorable stress profiles with relatively less degradation of the composite stiffness. The trends established are predicted to be essentially independent of the fiber volume fraction.