Analysis Of Elastic-plastic Buckling And Postbuckling Of Orthotropic Sheet Metal

In this thesis, a theoretical analysis of the elastic-plastic wrinkling of orthotropic sheet metal during the process of forming is systematically presented. Conclusions given herein not only contribute to the enrichment and development of plasticity ' theory, but also provide necessary theoretical basis for the engineering practices.Firstly, a new yield criterion is proposed, in this thesis, to describe mixed hardening of orthotropic materials, including kinematic hardening and proportional hardening, which avoids the flaw that the yield criterion is irrelevant to hydrostatic pressure in Hill's criterion, and the associated plastic flow law is derived. Accordingly , the elastic-plastic constitutive equations of mixed hardening of orthotropic materials are obtained, which is suitable for complicated stress condition and complicated stress history. And it can reflect the effect of material's plastic deformation history on the current stress-strain relation.Secondly, based on the above-mentioned the constitutive equations of mixed hardening orthotropic materials and the Hill's bifurcation-point buckling theory, the elastic-plastic buckling equations of orthotropic thin plates subjected to non-homogeneous in-plane compression are established and the critical stresses calculated. Furthermore, the influences of several factors,,such as geometry of plates, boundary condition and ratio of loads along two directions, etc. on the elastic-plastic critical stresses are discussed.Thirdly, using AM6apu.yM.HH's refined theory of moderately thick anisotropic plates, the patterns of the influence of transverse shear deformation, geometry and ratio of loads along two directions on the elastic-plastic buckling critical loads of moderately thick plate are analyzed.Additionally, the elastic-plastic post-buckling behavior of orthotropic sheet metals is investigated. Special interest is devoted to load-deflection path and the maximum support load.All of the results in this thesis can degenerate into isotropic, even elastic cases. So, they are more flexible. When plate is buckled, it just loses its uniqueness of in-plane equilibrium state, not stability. Sheet metal has stable elastic-plasticpost-buckling path. Only when the applied load surpasses the maximum support load of plate, the transverse deflection will grow unstably. Namely, plate loses its stability in elastic-plastic range. This means that engineers can use the conclusions given herein as a theoretic basis for preventing and eliminating the wrinkle during the processing of sheet metal forming.