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Parameter determination of advanced cyclic plasticity models which are developed for simulation of cyclic stress-strain and ratcheting responses is complex. This is mainly because of the large number of model parameters which are interdependent and three or more experimental responses are used in parameter determination. Hence the manual trial and error approach becomes quite tedious and time consuming for determining a reasonable set of parameters. Moreover, manual parameter determination for an advanced plasticity model requires in-depth knowledge of the model and experience with its parameter determination. These are few of the primary reasons for advanced cyclic plasticity models not being widely used for analysis and design of fatigue critical structures. These problems could be overcome through developing an automated parameter optimization system using heuristic search technique (e.g. genetic algorithm). This paper discusses the development of such an automatic parameter determination scheme for improved Chaboche model developed by Bari and Hassan [4]. A new stepped GA optimization approach which is found to be more efficient over the conventional GA approach in terms of fitness quality and optimization time is presented.

Ratcheting is defined as the accumulation of strain or deformation in structures under cyclic loading. Damage accumulation due to ratcheting can cause failure of structures through fatigue cracks or plastic collapse. Ratcheting damage accumulation in structures may occur under repeated reversals of loading induced by earthquakes, extreme weather conditions, and mechanical and thermal operating conditions. A major challenge in structural and solid mechanics is the prediction of ratcheting responses of structures under any or combination of these loading conditions. Accurate prediction of ratcheting-fatigue and ratcheting-collapse is imperative in order to incorporate the ratcheting related failures into the ASME design Code in a rational manner. This would require predictions of both local (stress-strain) and global (load-deflection) responses simultaneously. In progressing towards this direction, a set of experimental ratcheting responses for straight and elbow piping components and notched plates is developed. Advanced cyclic plasticity models, such as, modified Chaboche, Ohno-Wang, and AbdelKarim-Ohno models, are implemented in ANSYS for simulation of these experimental responses. Various integration schemes for implementing the constitutive models into the structural analysis code ANSYS are studied. Results from the experimental and analytical studies are presented and discussed in order to demonstrate the current state of simulation modeling of structural ratcheting.

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Ratcheting damage accumulation in piping components may occur under repeated reversals of loading induced by earthquakes, mechanical and thermal operating conditions, and other extreme loading conditions. Ratcheting damage accumulation can cause failure of structures through fatigue cracks or plastic collapse. A major challenge in structural mechanics is the prediction of ratcheting responses of structures under various cyclic loading conditions. Accurate prediction of ratcheting-fatigue and ratcheting-collapse of elbow components is imperative in order to incorporate the ratcheting related failures into the ASME design Code in a rational manner. This would require predictions of both local (stress-strain) and global (load-deflection) responses simultaneously. Towards achieving this goal, a set of experimental responses of elbow piping components is developed. Advanced cyclic plasticity models, such as, modified Chaboche, Ohno-Wang, modified Ohno-Wang and Abdel Karim-Ohno, are implemented into ANSYS for simulating the experimental responses. Results from the experimental and simulation studies are presented in order to demonstrate the state of structural ratcheting response simulation by these models.