An Alternative Constitutive Equation for Superplasticity
Different models have been put forward to explain superplasticity. Most of the models predict the independency of activation energy (Q) on stress. Superplasticity is observed in region II of creep curve (logε Vs σ/E). The most commonly considered mechanism for superplastic flow involves Grain Boundary Sliding (GBS), and it is necessary for an accommodation process to accompany GBS. The accommodation process might be grain boundary migration, recrystalisation, diffusional flow or some dislocation slip process. But the Arrhenius type of equation given by Becker gives the dependency of activation energy on stress. Here in this work we have considered this equation and relation between Q and σ is found out using genetic algorithm. The present model development studies the parameter optimization, where parameters appearing in the stress and energy relationship equation e.g. relationship between Q(σ) and σ for the Q(σ) equation given in present work as well as pre-exponential factors are optimized with the objective function being the error minimization of model predicted values and experimental data of strain are available from open literature.
T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran
B. Naik "An Alternative Constitutive Equation for Superplasticity", Materials Science Forum, Vols. 539-543, pp. 2865-2871, 2007