Constitutive equation for the hot deformation behavior of C_sf/AZ91D composites and its validity for numerical simulation

The flow stress behavior of 10 vol. % short carbon fibers reinforced AZ91D composites (C_sf/AZ91D) were investigated by hot compression test. The results show the flow stress reach the peak value at small strain and then decrease monotonically until the end of the large strain, which exhibits an obvious dynamic strain softening. The decrease of stress level with deformation temperature increasing or strain rate decreasing can be represented by Zener–Hollomon parameter in a hyperbolic sine equation. By considering the effect of strain on material constants, a modified viscoplastic constitutive equation was established to characterize the dependence of flow stress on the deformation temperature, strain, and strain rate. The stress-strain values calculated by the constitutive equation are in consistent with the experimental results. Applying the constitutive equation, the plastic deformation of C_sf/AZ91D composites during the hot compression process were analyzed by finite element simulation. The calculated punch force-stroke curves agree well with the measured ones. The results confirmed that the established constitutive equation can accurately describe the hot plastic deformation behavior of C_sf/AZ91D composites, and can be used for the finite element analysis on the hot forming process.