Open-die forging of structurally porous sandwich panels

Structurally porous metal sandwich panels consisting of dense face sheets a nd porous cores of controlled relative density can be manufactured by trapp ing inert gas during hot isostatic pressing and modifying its distribution via subsequent thermomechanical forming. A plane-strain solution for analyz ing the open-die forging of such a plastically compressible sandwich panel is developed. An effective yield potential for the face sheet/core sandwich is constructed from the Mises yield criterion for the rigid-plastic face s heet and Doraivelu et al's density-dependent yield function for the compres sible core. This effective constitutive response is used in a classical "sl ab" analysis of open-die forging. The analysis predicts the upsetting force and the distributions of pressure, core relative density, and average stre sses within both the face sheet and the core. During upsetting, a zone of f ully constrained material (i.e., with zero lateral strain) is predicted to occur at the center of the workpiece, and this densifies first. A densifica tion front then advances laterally from the panel center toward the outer e dges. The nonuniform densification complicates the use of forging for the p roduction of components requiring a uniform density core.