Transient Creep Strain of a Fiber-Reinforced Metal-Matrix Composite Under Transverse Loading

Based on the combination of Mori-Tanaka’s mean-field concept and Luo-Weng’s solution of a three-phase cylindrically concentric solid, a local-field theory is developed to study the evolution of stress distribution in the ductile matrix and the time-dependent creep strain of a fiber-reinforced metal-matrix composite. Due to the nonlinear stress dependence in the creep rate and the highly heterogeneous nature of the transverse deformation, this local theory is shown to provide a more accurate estimate for the overall transverse creep of the composite than the simpler meanfield theory (the difference between the two however is not significant in the axial tensile creep). The disclosed transverse stress field in the matrix is truly heterogeneous, with the 45 deg region exhibiting a substantially higher effective stress than the 0 deg and 90 deg regions. The stress in the higher stress region is found to decrease continuously; it is passed on to the fibers and thereby serves as an important creep-strengthening mechanism for the composite. The interfacial tensile stress at the pole, which is the highest stress point around the interface, is seen to grow continuously and becomes a potential site for a later creep debonding. The developed micromechanical theory is finally applied to predict the transverse tensile creepstrain of a Borsic/aluminum composite, and the result is found to be in close agreement with the test data.