Viscoplastic constitutive equations for modeling fluid loading and damage evolution during warm medium forming

Abstract

A unified viscoplastic constitutive model is proposed coupling fluid pressure rate control and damage evolution for warm medium forming (WMF), which also includes flow stress function, hardening law and dislocation density evolution. The pressure rate and damage behavior are investigated based on the experimental data of Ref. (Lang et al., 2013) [10] and the fracture morphology observations of specimens. The constitutive equations are discretized and derived through the fourth-order Runge-Kutta method. Meanwhile, the material constants of this model are determined using the Genetic Algorithm. The proposed constitutive model is applied to the WMF process of AA7075-O sheet and compared with the results of Ref. [10]. The error between calculated and experimental data is quantified using the average absolute relative error (AARE). Results indicate that the prediction accuracy of the proposed constitutive model is significantly improved compared with Ref. [10], also, the predictions compare well with the experimental results. The new constitutive model can effectively predict the flow behavior of AA7075-O in WMF.