A New Hardening Model Of Metal Constitutive Equations

In this thesis we have described a newly developed elastic-platic constitutive model and developed the hardening rule whose application in some load paths is discussed.Two types of hypersurface ,a yield surface and a memory surface ,are definiend and each is described by a different hanrdening rule .The current memory surface memorizes the maximum stress experienced by the material in loading history ,and indicates the hardening exent of the material ;The limit memory surface memorizes the maximum stress before destruction. The yield surface always remains inside the memory surface and portrays the locus of the elastic region .these two surface separate the material behavior into three distinct zones: an elastic zone contained within the yield surface, a plastic zone between the yield surface and the current surface confined within the prior history and a plastic zone between the yield surface and the limit surface.Their combination can model complex loading situations ,including cyclic loading and closed-loop loading . Based on the experimental observations ,the hardening modulus curve is proposed to predict change in size of the subsequent yield surface from the stress -strain relation of the material .A new evolution of the yield surface is described with simple mathematical expressions .The constitutive relation in 2-dimensions was reduced .Finally we have prospected the further development of the two-surface model.