AN INCREMENTAL ELASTIC-VISCOPLASTIC THEORY INDICATING A REDUCED MODULUS FOR NONPROPORTIONAL BUCKLING

The small deformation elastic-viscoplastic constitutive equations of B odner-Parlom are modified to model strong non-proportional loading pat hs such as experienced in corner turning tests and certain cases of in elastic buckling. An essential generalization is made to the flow rule , causing the magnitude and direction of plastic strain rate to become an explicit function of deviatoric total strain rate as well as of st ress and hardening variables. With this and other modifications, the e quations indicate some of the important characteristics of the respons e to abrupt changes in the loading direction. These are: (a) a reduced effective shear modulus; (b) a transient drop in the effective stress ; and (c) a transient non-coaxiality of the plastic strain rate relati ve to the deviatoric stress. Predictions of the modified theory compar e reasonably well with experimental values for inelastic torsional buc kling of axially compressed cruciform columns and for corner turning t ests.