A consistent modified Zerilli-Armstrong flow stress model for BCC and FCC metals for elevated temperatures

The Zerilli-Armstrong (Z-A) physical based relations that are used in polycrystalline metals at low and high strain rates and temperatures are investigated in this work. Despite the physical bases used in the derivation process, the Z-A model exhibits certain inconsistencies and predicts inaccurate results when applied to high temperatures-related problems. In the Z-A model, the thermal stress component vanishes only when T -> proportional to. This contradicts the thermal activation mechanism that imposes an athermal behavior for the flow stress at certain finite critical temperatures. These inconsistencies, in fact, are attributed to certain assumptions used in the Z-A model formulation that causes the model parameters to be inaccurately related to the microstructural physical quantities. New relations are, therefore, suggested and proposed in this work using the same physical bases after overcoming any inappropriate assumptions. The proposed modified relations along with the Z-A relations are evaluated using the experimental results for different bee and fee metals. Comparisons are also made with the available experimental results over a wide range of temperatures and strain rates. The proposed model simulations, in general, show better correlation than the Z-A model particularly at temperatures values above 300 K degrees. Numerical identification for the physical quantities used in the definition of the proposed model parameters is also presented.