Mokhtar Awang

Date of Graduation

2007

Document Type

Dissertation/Thesis

Abstract

Recently, friction stir spot welding (FSSW), a variant of “linear” friction stir welding (FSW) has received considerable attention from automobile industries to replace electric resistance spot welding with aluminum frames. Thus far, the FSSW process has been successfully developed and applied in various cases, but the physics behind the process is not yet fully understood. Effective and reliable computational models of the FSSW process would greatly enhance the study of friction phenomena during the process as well as energy dissipation. Approaches for the computational modeling of the FSSW process, however, are still under development and much work is still needed, particularly the application of explicit finite element codes for a verifiable simulation. The main objective of this dissertation research is aimed at describing the friction phenomena and heat generation during FSSW process. To achieve this objective, a three-dimensional fully coupled thermal-stress finite element (FE) model has been developed in Abaqus/Explicit code. The simulation model utilizes the advantages offered by the arbitrary Lagrangian Eulerian (ALE) formulation in simulating severe element distortion using an adaptive mesh scheme. Rate dependent Johnson-Cook material model is used for elastic plastic work deformations. Since friction in FSSW cannot be effectively treated by a simple “friction coefficient”, a friction coefficient, which is dependant on pressure, temperature and slip rate is used with sliding Coulomb friction at the interface between the workpiece and the welding tool. The simulation results include temperature, stress and strain distributions as well as frictional dissipation energy, which are presented at the end of this dissertation. The peak temperature at the tip of the pin and frictional dissipation energy are in close agreement with the experimental work done by Gerlich et al. [1], which is about 5.1% different.

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