TENSILE-STRENGTH OF UNIDIRECTIONAL COMPOSITES - THE ROLE OF EFFICIENCY AND STRENGTH OF FIBER-MATRIX INTERFACE

A micromechanics model has been developed to predict the tensile stren gth of unidirectional composites. The local stresses are calculated us ing shear lag analysis, including the effects of interfacial debonding . The tensile strength of the composite is estimated by considering th e accumulation of fiber fractures as a function of applied load. A new parameter called 'efficiency' of the interface is introduced to accou nt for the effectiveness of load transfer from the matrix to the fiber . A simple scheme is described to estimate this efficiency parameter s l using the experimentally measured tensile stiffness in the concentri c cylinders model. It is postulated that the interface can be complete ly characterized by two parameters: interfacial shear strength tau(i) and efficiency of the interface eta. Results indicate that the interfa cial 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 po ssessed care fully tailored interphase variations. The predicted tensi le strengths agree well with the experimental data The predicted failu re modes in these material systems are also consistent with experiment al observations.