Experimental Study On Uniaxial Ratcheting Effect Of Polycrystalline Copper And Research On Crystal Plasticity Constitutive Model

Ratcheting,a cyclic accumulation of inelastic deformation occurred in the engineering materials and structures subjected to asynmetrical stress-controlled cyclic loading.If the ratch-eting was occurred during the structures or devices working,excessive ratcheting strain would lead to plastic deformation failure,and also reduce the fatigue life of the structures.Therefore,it should be considered when evaluating the reliability,safety and fatigue life of the structure.In recent years,many scholars have studied the ratcheting of materials,and have obtained many research results.However,because of the complexity and diversity of the ratcheting,there are many problems that have not been solved.For example,experimental research is not enough comprehensive and specific,and most of the existing models are phenomenologically con-structed and they can't reflect the microscopic physical mechanisms of ratcheting.Therefore,in this dissertation,a research has been made on uniaxial ratcheting experiment for polycrys-talline copper and the polycrystalline cyclic constitutive model was conducted in the framework of crystal plasticity.The main contents of this dissertation involve:(1)The experiment for polycrystalline copper was investigated under uniaxial tension,strain control cycle and asymmetric stress control cycle loads,and the cyclic characteristics of copper and the ratcheting evolution law under different working conditions were obtained.They are helpful to construct the corresponding constitutive model and ensure the values of the pa-rameters.(2)Based on crystal plasticity theory,the visco-plasticity main control equation of single crystal was constructed.The self-hardening and potential hardening rule,modified A-F kine-matic hardening rule and explicit transition rule were introduced to construct a polycrystalline constitutive model which can describe ratcheting.(3)The uniaxial ratcheting of polycrystalline copper was simulated and predicted by using the modified constitutive model.Compared with the experimental results,the accuracy of the model was verified.In addition,the prediction of the ratcheting in the single crystal scale was also carried out.