Analysis And Research On The Forming Limit Of A Zirconium Alloy

The fabrication technology of spacer grid strip used in nuclear fuel assembly is an essential part of the nuclear industry manufacturing system,however,the strips used in our country still mainly rely on imported.Generally,strips are manufactured by sheet metal forming and the forming materials are mainly zirconium alloys.Forming limit curve,as an important method to evaluate the forming performance of sheet metal,can be considered as an effect way to improve the formability of the specific sheet metal used in the strip fabrication area.This study is based on the national major special project and the research object is the new zirconium alloy sheet(nominal thickness is about 0.457mm)with the nominal composite of Zr-Sn-Nb-Fe.During this study,the forming limit curve is acquired by both theoretical calculations and physical experiments.The main factors influenced on the formability of this zirconium alloys are also analyzed.The theoretical analysis part can be stated as follows: Firstly,the basic plastic theory related to the sheet metal forming is introduced,including a variety of anisotropic yield criteria as well as the unstable models.Then,several forming limit curve theoretical models such as Hill48-Swift-Hill,Hosford79-MK and Barlat89-modified M-K models are programed.Moreover,the calculation results of the FLCs by different theoretical models are compared and the initial parameters are optimized.Finally,a software for a variety of theoretical systems is developed and packedThe numerical simulation part of this study can be depicted as follows: First of all,the Barlat89 yield criterion is selected to describe the plastic behavior of the zirconium alloy during the simulation of the Nakazima test.The ratio of the strain rate difference between the necking element and its neighboring elements is used as the criterion of instability,and then the finite element analysis results are compared with the physical test results,which proves the accuracy of the finite element model,and provides information for analyzing the influence mechanism of the strip characteristics.And then,by adopting the same finite element material model,the formation of the rigid convexity of the typical features in the strips is studied.The concept of safety margin is introduced,and the influence of the layout method,process parameters and material parameters on the formation of the feature is studied through the analysis of the corresponding strain path.Finally,a method to improve the forming performance of rigid-convex characteristics is proposed,which provides a research idea for improving the forming performance of zirconium alloy.