Nickel-based Alloy Nuclear Fuel Spacer Grid Stamping Numerical Simulation And Experiment Study

Stamping is very widely used in sheet metal forming.Deformation conditions are very complex and forming quality can be influenced by many factors during the stamping process.Generally,numerical simulation is applied to simulate the sheet forming process and predict defects such as wrinkling,fracture and spring-back prior to manufacturing of the parts.Speaking of numerical simulation,proper material model,yield criteria and failure criteria are the key prerequisites for obtaining accurate results.Nuclear fuel spacer grid is a typical kind of sheet metal part used in energy industry.However,the simulation study of its stamping process is relatively rare at present.In addition,Inconel 718 is widely used in grid stripe manufacturing because of its good properties at high temperature.Previously,study of Inconel 718 mainly concentrated on the composition improvement and high-temperature properties,lacking of systematic research on its cold forming performance.In this paper,cold forming properties of Inconel 718 rolling sheet metal,including tensile mechanical properties,strain rate sensitivity,anisotropy in the plate plane and extrapolation of stamping flow stress model,are systematically studied by running numerical simulation of the nuclear fuel grid stripe stamping process.Three-dimensional finite element simulation of the punching process and the subsequent bending process considering damage accumulation is performed.The conclusions are as follows:?1?Mechanical properties of Inconel 718 sheet at room temperature are measured.From the results,Anisotropy is studied in the plane of the sheet.Then strain ratio r₀,r₄₅,r₉₀ are calculated and strain rate sensitivity at room temperature is analyzed.It is proved that the yield stress,yield ratio and strain hardening exponent follow the same trend of strain rate.Among the four fracture criterion,Oyane can best predict the Inconel 718fracture surface quality.Freudenthal and Brozzo criterion can well predict the smooth zone width but can not well predict the burr length.Finally the Oyane criterion is selected for the 3D punching simulation.?2?Critical value of plastic fracture of the material is obtained by calculating equivalent strain in the uniaxial stretching experiment.Then the value is introduced into the ABAQUS/Explicit module by VUMAT user routine.By comparing the result of the simulation and experiment,it is found that Oyane criterion can provide the best prediction of the fracture surface quality,while Freudenthal and Brozzo criterion the width of the smooth zone.But the latter gives a poor prediction of the shape and height of the burr.Rice&Tracey criterion also gives a poor prediction of the fracture surface quality.?3?By comparing the simulation and experiment results,it can be found the simulation fits well with the experiments in terms of the length of the burrs and roll-over,while poorly in terms of the width of the smooth zone.Considering the asymmetry of the profile and anisotropy of the material,the reason of the non-uniform distribution of the smooth zone is analyzed.?4?Considering the damage residue after the stamping,corresponding projection of the initial damage in the post-bending process is brought up according to the shape feature of the parts.Then the method is introduced into the simulation,simulation of the bending process is in good agreement of the experiments and provide a better prediction of the fracture.?5?A series of experiments are conducted,mechanical properties,strain rate sensitivity and anisotropy of the material Inconel 718 are analyzed.Then an extrapolation model of flow stress is established.All above provide important instruction for the simulation of the material.And the model considering the projection of the residual damage can provide a better prediction of the fracture caused by bending than the one without the projection,which can be instrumental in CAE analysis.