STEADY-STATE AND TRANSIENT CREEP-PROPERTIES OF AN ALUMINUM-ALLOY REINFORCED WITH ALUMINA FIBERS

Steady state and transient creep experiments have been conducted on a metal matrix composite consisting of an aluminum-5 wt% magnesium alloy matrix reinforced with 26 vol.% alumina fibers. The composite exhibits high steady state stress exponents which range from 12.2 at 200-degrees-C to 15.5 at 400-degrees-C. The apparent activation energy for creep over this temperature range is found to be 225 kJ/mol. After unloading, large anelastic strains are observed. The anelastic recovery process is found to vary non-linearly with stress and temperature and exhibits an activation energy of 151 kJ/mol. A finite element model of the composite microstructure has been developed by treating the alumina fibers as an interconnected network of elastic beam elements. This model accurately simulates the transient response of the material to changes in loading. The model suggests that the high stress exponents, high activation energy, and large recoverable strains observed for this material can be explained by a balance between load transfer to and damage of the fiber network.