A criterion for void closure in large ingots during hot forging

A quantitative investigation of the mesomechanism of void closure in large ingots during hot forging is undertaken in the present study. The constitutive relation of the void-free matrix is assumed to obey the Norton power law. A cell model which includes matrix and void is employed and a Ritz procedure is developed to study the volumetric strain-rate of the void. On the basis of a large number of numerical computations, a criterion for void closure in large ingots during hot forging is proposed. In addition, the significant effects of the Norton exponent, the remote stress triaxiality and the remote effective strain on void closure are revealed: (1) the volumetric strain-rate of the void increases monotonically as the stress triaxiality level and the Norton exponent of the material increase, (2) the remote effective strain required for void closure decreases as the stress triaxiality level and the Norton exponent increase and (3) the void becomes unstable and the collapse rate decreases at the final stages of void closure. With the criterion for void closure, process design and optimization in terms of elimination of voids in large ingots will be convenient since the criterion can be easily applied in CAE analysis.

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