High temperature creep of planarly isotropic metal-matrix and polymer-matrix composites

The time-dependent creep behavior of a two-phase composite containing randomly oriented spheroidal inclusions in a 2-dimensional plane is studied for both metal-matrix and polymer-matrix systems. In the former case the creep rate depends on the stress nonlinearly whereas in the latter its creep behavior is represented by the linear viscoelastic solid. The nonlinear nature of the problem implies that the theory developed for the metal-matrix composite is suitable primarily for the short-time transient creep at a dilute concentration. No such restrictions are placed on the polymer-matrix composite. It is found that, for both types of composite, needles or discs usually provide the most effective strengthening mechanism in the isotropic plane, whereas spherical particles usually rank as the poorest agent. In the out-of-plane direction, discs consistently give the most superior creep resistance. Some differences in the trend of the inclusion-shape dependence on these two classes of composite, are observed, and this is in part attributed to the assumption that the creep behavior of metal matrix is incompressible and insensitive to the hydrostatic stress, whereas the viscoelastic property of the polymer matrix is compressible and also sensitive to the hydrostatic pressure.