Yield Function for Structural Porous Metals

Abstract

To reduce weight while maintaining high specific strength, Structural Porous Metals (SPM) are being developed. These materials are alloys containing an inert gas in distributed pores at very high pressures. The pores of gas are incorporated into SPM during processing. Since the pores are closed pores at high pressures, the material can be processed by standard methods such as rolling or forging without collapsing the gas pores. These materials must be treated as a composite material with special deformation behavior under applied stresses. It should be noted that, unlike solids, shear stresses can not be present in a gas medium in static equilibrium. This paper deals with the determination of the yield stress of structural porous metals. The yield function is calculated from the principle of virtual work. In this approach it is assumed that a constant amount of energy needed to deform the material to the yield point. In the case of SPM, the yield function must include the work needed to deform the gas pores as the material yields. The energy of deformation for the gas in the pores is evaluated according to the ideal gas law. The total work done in deforming the gas and the solid metal is taken into account in determination of the yield function of SPM. The result of the analysis is then compared with classic yield functions for monolithic alloys.