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A. R. Ragab 《Metallurgical and Materials Transactions A》2006,37(4):1281-1287
This work presents a unified approach to predict surface strains at failure in bulk forming processes. The approach does not
deal with a specific process but rather with prescribed strain and stress paths. The material to be processed is assumed to
possess an initial void volume fraction that grows and colaesces with straining, ending by fracture. The predictions are based
on a formulation for voided solids according to the Gurson-Tvergaard yield function adapted to include orthotropic anisotropy.
The incident of fracture is characterized by shear band formation within the ligaments of the matrix material among spheroidal
voids as described by McClintock. The results are represented by a straight line plot of tensile limit strain versus the compressive
strain for different loading paths. These limit curves are shown to be dependent on the initial void fraction, hardening,
and anisotropy of the matrix matrial. Alloys with lower initial void fractions as well as those of higher hardening show better
workability. The model is applied to predict bulk formability curves for steels AISI 1040 and 1045, Aluminum AI 7075-T6, and
copper, based on the proper selection of micromechanical parameters for these alloys. The validity of the model is ensured
through fairly favorable comparison with experimentally determined limit curves. The current failure conditions are suitable
to predict the experimental dual slope fracture line that may exist for some alloys such as cold-drawn steel AISI 1045 and
aluminum 2024-T6 by considering two mechanisms of failure: internal necking in the ligament material between voids, followed
by transition to shear band formation. 相似文献
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