The Shakedown Analysis Method For The Huge Complex Mechanical Structure And Its Application

The local high stress commonly occurs in the key complex components of the loaded hadraulic press frame structure. The application of the elastic mechanics theory for the structure strength analysis is not suitable for the local high stress as well as the local plastic deformation. The elastic-plastic strength design rule with the shakedown theorem allows local plastic deformation to occurr, on the premise that the structure is under safety working condition. Then it can analyze and solve the structural strength problem with local high stress. So the shakedown therorm is introduced into the strength analysis of the hydraulic press frame. The establishment of the shakedown analysis method takes into account the kinematic hardening of the material, and it is sutiable for the huge complex structure under the combination of the constant and cyclic loads.The expanded shakedown lower bound theorem for the limited kinematic hardening structure is applied. The self-equilibrium stress field is constructed. The general analytical solution of the shakedown limit load is derived by analytical analysis. The shakedown limit loads for the symmetrical cyclic loading and the un-symmetrical cyclic loading are both deduced too. The hollow speimen subjected to constant tension and full reversed cyclic torsion, and non-full reversed cyclic tension, a flanged pipe subjected to non-fully reversed cyclic internal pressure and axial force, and a thin square plate with a small central hole subjected to biaxial cyclic tension are all analysed. The analytical result of this paper is verified by some solutions in other literature.The Polizzotto’s expanded shakedown lower bound theorem for the combined loading is applied. The stress field equilibrium with the external constant load is constructed. Then the shakedown condition corresponding to the constructed stress field is proposed. The shakedown behavior of the structure under the combined loading is analyzed by the analytical analysis of the shakedown condition. The general shakedown limit load under the combined loading is resolved. The hollow speimen subjected to constant tension and full reversed cyclic torsion is analysed. The general analytical solution of this paper is compared to other detail solutions in the literature and discussed.In consideration of the properties of the common structural material and the conditions of the loading, the time independent stress field equilibrium with the constant external load and the time independent back stress field are both constructed, and the corresponding shakedown condition is derived. The specified loading path isproposed. With the utilization of the incremental elastic-plastic finite element technique, a shakedown numerical analysis method is proposed to solve the shakedown limit load of the huge complex structure effectively. The shakedown experiment for the square plate with central hole of Q235 steel is performed. The shakedown numerical method is verified by the experimental result. The established shakedown numerical method are applied to a cylinder body of the hydraulic cylinder for a huge forging hydraulic press, and a crown of another huge forging hydraulic press. The shakedown limit loads are caclutated and the elastic-plastic safety margin are given, respectively.