Aluminum alloy 7075 ratcheting and plastic shakedown evaluation with the multiplicative Armstrong-Frederick model

This work investigates experimentally and computationally the uniaxial ratcheting strain and plastic shakedown of aluminum alloy 7075-T6. The experimental results illustrate the existence of both plastic shakedown and cyclic hardening, proving that both kinematic and isotropic hardening should be included in modeling. Although the multicomponent Armstrong-Frederick model with multiplier has demonstrated high accuracy in aluminum ratcheting simulation, as well implementation ease, the present results demonstrate poor performance when plastic shakedown is considered. This is attributed to the limited flexibility in varying the model parameters to balance the loading/unloading branches in the hysteresis loops and decelerate ratcheting pace. To improve the ability of the multicomponent Armstrong-Frederick model with multiplier in simulating plastic shakedown, a modification was made within the framework of the model that includes multiple backstress components, with each obeying its own kinematic hardening. A linear kinematic hardening backstress was added in the formulation, enabling the control of ratcheting pace and the occurrence of plastic shakedown. Simulations with the modified multicomponent Armstrong-Frederick model with multiplier demonstrate a significantly improved capability for ratcheting and plastic shakedown. Moreover, the modified multicomponent Armstrong-Frederick model with multiplier improved the life prediction for an actual aerospace structure. This provides a strong indication of the importance of achieving plastic shakedown accuracy when simulating cyclic elastoplastic behavior. Read More: