Study On Local Plastic Deformation Of A Hydraulic Press Beam Under Cyclic Loading

The upper crossbeam of hydraulic press is often subjected to alternating load instead of single load in actual production.Under the action of alternating load,the upper beam will cause plastic deformation in local high stress area due to ratcheting effect.The ratcheting strain generated by the ratchet effect accumulates over time and increases the deformation of the local shape,which leads to the destruction of the beam structure.For a long time,when designing and checking crossbeam of hydraulic press,elastic strength limit is usually regarded as the ultimate bearing capacity of structural materials,and plastic deformation is not allowed.But the engineering practice shows that the structure still has the corresponding bearing capacity when the material has local small plastic deformation.If the limit of the elastic limit can be broken through,the bearing capacity of the material can be further excavated so that the weight reduction of the mechanical equipment can be realized.Therefore,it is necessary to study the deformation characteristics of the upper crossbeam of a hydraulic press on the local high stress area when subjected to cyclic loading,summarize its evolution rule,and further provide theoretical basis for the lightweight design of hydraulic press.In this paper,the hydraulic machine commonly used materials Q235 steel is used as the research object.Under the room temperature,the tensile test,strain control and stress control of cyclic loading tests were carried out on Q235 steel.Through research and analysis of the experimental data,the basic characteristics of the uniaxial strain cyclic deformation behavior and the ratchet behavior of Q235 steel were obtained.In this paper,the simplified horizontal beam of hydraulic press is used as the research object,and the 1:10 shrinkage model is designed.At room temperature,uniaxial tensile test and asymmetrical stress controlled cyclic loading test were carried out for Q235 steel plate used in shrinkage model of hydraulic press upper crossbeam,and its basic mechanical properties and ratcheting deformation characteristics at room temperature were obtained.A simple and feasible method was used to determine the material parameters of model,then the test procedure were simulated.The results shows that the model in this paper was reasonable to describe the uniaxial strain cyclic deformation be-havior and the ratchet behavior of Q235 steel,The finite element implementation of the constitutive model was successful.A new cyclic elastoplastic constitutive model which can accurately describe the deformation behavior of Q235 steel ratcheting is embedded in ABAQUS,and the numerical simulation of the upper beam crosssection ratio model is carried out.The area of the upper beam structure under the asymmetric cyclic loading is determined,and the evolution of stress and strain with cycle times and its influence on the surrounding area are analyzed.A cyclic loading test system for upper beam of hydraulic press is designed and manufactured.According to the result of numerical simulation,the loading condition is determined,and the asymmetric cyclic loading test is carried out on the Instron8800 electro hydraulic servo fatigue tester.The conclusion of the numerical simulation of the beam on the hydraulic press is verified.The experimental results show that the conclusion of the numerical simulation of the beam on the hydraulic press is basically correct.