Numerical Simulation Study On Dynamic Strength Of Self-tightening Thick-walled Cylinder Under Moving Load

The calculation of stress and strain in the gun barrel during autofrettage process must be accurate,which is the theory base of follow up designing the barrel dimensions and fatigue life.In this dissertation,thick-walled cylinder was taken as research project.To describe the autofrettage process,a mathematical formula,a constitutive model and the consistent tangent modulus associated with constitutive model were constructed.Based on the constitutive model,the residual stress release rule of autofretted thick-walled cylinder subjected to moving load was researched.Main contents in this dissertation are as follows:(1)Derivation of residual stress formula of autofretted thick-walled cylinder.According to thick-walled cylinder assumption and elastic-plastic theory,the stress formula in elastic and plastic region at loading and unloading stage were calculated respectively so the final residual stress formula was obtained.By utilizing the MATLAB software and calculating examples,the validity of formula was verified.As the result showed,the derived residual stress formula could accord with test.(2)Constructing material constitutive model and the consistent tangent modulus.A nonlinear mixed hardening model was proposed based on AF model,and this model showed the nonlinear stress-strain relationship and the evolution rule of yield surface whose size decreases with the increasing of plastic deformation.In this model,the back stress was divided into several parts,and every part obeyed the back stress evolution rule of AF model.Besides,the nonlinear isotropic hardening model reflecting the Bauschinger effect was also included in the model.Using the proposed constitutive model and the elastic-plastic relationship among parameters,a tensor-form consistent tangent modulus was derived for iterative solution and increasing the convergence speed of numerical calculation.The residual stress of an autofretted barrel was computed by utilizing FEA method,and the comparative analysis was conducted,which showed that the proposed model could be of higher precision than the other methods.(3)The residual stress release rule of autofretted thick-walled cylinder subjected to moving load.The VDLOAD subroutine was applied to constructing moving load model.Contrast tests on the change of stress under two load conditions subjecting on autofretted thick-walled cylinder were conducted,and these two load conditions were average pressure load and moving load respectively.The result indicated that the moving load corresponded with artillery firing process.The moving load model was utilized to autofretted thick-walled cylinder for simulating the change of chamber pressure when artillery fired,which showed that the residual stress of autofretted thick-walled cylinder was a damped exponential law.