Preliminary Research On Numerical Simulation Of Friction Stir Welding By Rigid-viscoplastic Dynamic Explicit FEA

Friction stir welding, as a rapid developing new solid-phase welding technology, iswidely used in aerospace, automotive, shipbuilding and other industries for theadvantages such as high material compatibility, joint quality etc. Recently, the researchon the formation mechanism of the friction stir welding joint structure is still at theinitial stage. Numerical simulation can reproduce the plastic strain and flow of the weldmetal. Numerical simulation avoids expensive experiment, and it is a effective researchapproach to know the formation mechanism of the friction stir welding joint structure.In this paper, the key techniques in the rigid viscoplastic dynamic explicit FEM arestudied. The finite element analysis program of friction stir welding and itspost-processing system have been developed by the authors, and it is of importance tothe development and application of the friction stir welding technology. A briefintroduction to the research and its main achievements obtained are as follows.In this paper, the rigid viscoplastic dynamic explicit finite element equation isdeveloped by using a virtual power equation. And the displacement-type explicitformulation is achieved through using central difference method, so that theconvergence problem owing to strong nonlinear phenomena of geometry, material andcontact can be avoided. And an algorithm is developed to calculate element stress andstrain from node displacement.According to the nonlinear contact problems in the dynamic finite elementcalculations of the friction stir welding, a new contact search algorithm is proposed,which includes global searching and local searching. And then a calculation modelwhich is employed to calculate normal contact force and tangential friction force isestablished to determine the contact force between tool and workpiece.In this paper, the treatment of hourglass modes which arise due to one-pointintegration in dynamic explicit algorithm is discussed. The hourglass control schemewhich eliminate hourglass problem is adopted in the research.Based on the system analysis and design, the data structure design, data flow diagram analysis and design of the simulation system are conducted, and some criticaltechniques of the solver are studied. By modularization design method, a finite elementcode of rigid viscoplastic dynamic explicit algorithm is developed to simulatethree-dimensional friction stir welding process. And then the plunging process of thetool is simulated with the established finite element analysis code, detail numericalresults are obtained, such as distributions of strain and stress.By using system analysis method and object-oriented design method, need analysis,function module partition, class diagram partition and design are conducted, and thestructure of the post process system are developed, and then develop the post processmodule of friction stir welding. This post process realized well the function ofdisplaying the result of the deformation, the stress and strain distribution of theworkpiece in friction stir welding process.