A novel evolutionary algorithm for determining unified creep damage constitutive equations

The determination of material constants within unified creep damage constitutive equations from experimental data can be formulated as a problem of finding the global minimum of a well defined objective function. However, such an objective function is usually complex, non-convex and non-differentiable. It is difficult to be optimised by classical gradient-based methods. In this paper, the difficulties in the optimisation are firstly identified. Two different objective functions are proposed, analysed and compared. Then three evolutionary programming algorithms are introduced to solve the global optimisation problem. The evolutionary algorithms are particularly good at dealing with problems which are complex, multi-modal and non-differentiable. The results of the study shows that the evolutionary algorithms are ideally suited to the problem. Computational results of using the algorithms to determine the material constants in a set of physically based creep damage constitutive equations from experimental data for an aluminium alloy are presented in the paper to show the effectiveness and efficiency of the three evolutionary algorithms. (C)) 2002 Elsevier Science Ltd. All rights reserved.