Tensile Strength of Unidirectional Composites: The Role of Efficiency and Strength of Fiber-Matrix Interface

Abstract

A micromechanics model has been developed to predict the tensile strength of unidirectional composites. The local stresses are calculated using shear lag analysis, including the effects of interfacial debonding. The tensile strength of the composite is estimated by considering the accumulation of fiber fractures as a function of applied load. A new parameter called ‘efficiency’ of the interface is introduced to account for the effectiveness of load transfer from the matrix to the fiber. A simple scheme is described to estimate this efficiency parameter η using the experimentally measured tensile stiffness in the concentric cylinders model. It is postulated that the interface can be completely characterized by two parameters: interfacial shear strength τi and efficiency of the interface η. Results indicate that the interfacial strength and efficiency can be optimized to maximize the tensile strength of a unidirectional composite. The proposed model was used to predict tensile strength of three different sets of materials that possessed carefully tailored interphase variations. The predicted tensile strengths agree well with the experimental data. The predicted failure modes in these material systems are also consistent with experimental observations.