A Micromechanics Model for Predicting the Tensile Strength of Unidirectional Metal Matrix Composites

Abstract

In this paper, a micromechanics model has been developed to predict the tensile strength of unidirectional metal matrix composites (MMC). A simplified shear lag analysis is used to estimate the local stresses in the various constituents (fiber/matrix/interface). In this work, the matrix is assumed to carry both normal and shear stresses. Global matrix plasticity is considered by assuming that the matrix behaves in an elastic-perfectly plastic manner. Local interfacial debonding is assumed to occur when the average interfacial shear stress exceeds the interfacial shear strength value. The shear lag analysis including the effects of interfacial debonding and global matrix plasticity is used to estimate the stress concentration in fibers adjacent to broken fibers and the ineffective length. The tensile strength is estimated by considering the accumulation of fiber fractures. The effects of residual thermal stresses and statistical distribution of strength of the fibers are also included in this analysis. Parametric studies were conducted to investigate the influence of various parameters such as fiber volume fraction, temperature, interfacial shear strength, matrix properties and fiber strength, on the unidirectional tensile strength of MMC. The model was also used to predict the effects of volume fraction and temperature, on the strength of SCS6/Ti 24-11 composites. The predicted values compared well with the experimental results.