Semester

Fall

Date of Graduation

2005

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Victor H Mucino

Abstract

Material flow in the solid-state Friction Stir Welding (FSW) is quite a complex process. The Investigation of the material flow can be carried out either by experimentation or by numerical simulation. However, compared to experimentation, numerical simulation is inexpensive, efficient and convenient, but quite challenging to model.;This work concerns the choice and development of numerical methods for efficient and reliable simulation of the material flow during FSW. The two objectives of this work are: to develop a mesh motion scheme for simulating the large deformations of the workpieces during FSW and to assess the material flow behavior of the rigid-elastoplastic problem of FSW using the moving mesh approach.;The challenging issue in modeling FSW is to deal with large deformations of the workpiece material. The Lagrangian simulations of FSW show that the severely distorted finite elements are caused due to the large deformation of workpiece material, which makes the Lagrangian approach inappropriate for modeling FSW. Thus, Arbitrary Lagrangian-Eulerian (ALE) formulations are used to overcome the shortcoming of Lagrangian formulations. The basic idea of the ALE approach is that the mesh is not obliged to follow the material flow. Thereby the excessively distorted elements can be avoided.;An important consideration in applying the ALE approach is an advection method which determines the mesh motion in every step of the analysis. Due to the characteristics of FSW, the moving mesh approach based on ALE formulations is developed for the modeling of FSW. Several case studies that document the material flow during FSW are presented using this approach.;Based on the simulation results, it is concluded that the material motion characteristics on the top surface and through the depth (volume) of friction stir welds have been made for the advancing and retreating sides. The motion trends are consistent with the reported experimental evidence. The case studies demonstrate the capabilities and potential of the mesh motion scheme in simulating the FSW process.

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