Modeling the constitutive response of bimodal metals

The mechanical response of metals with a bimodal grain-size distribution is modeled using the secant Mori-Tanaka (M-T) mean-field approach. The actual microstructure of bimodal metals involves a grain size distribution in the ultrafine and coarse regimes; the model approximates this in terms of two phases with distinct grain sizes and with specific volume fractions. The model is applied to two bimodal materials: the Al-5083 alloys of Laverniaet al. and the Cu of Wanget al. In both the materials, the predictions agree well with the experiments. In the bimodal Al alloy, the effect of extrusion on the anisotropy in yield strength and flow behavior is also addressed. Finally, based on the model predictions, an empirical expression of the Voce form is proposed to describe the overall flow behavior of both bimodal metals.