Coupled thermomechanical analysis of friction stir welding process using simplified models

It is widely recognised that the fundamental mechanisms associated with the weld formation process and their relationships with welding parameters are complex and remain to be fully understood. The present paper reports a ser ies of general findings based on a set of simplified numerical models that were designed to elucidate various aspects of the complex thermomechanical phenomena associated with friction stir welding. The following phenomena we re investigated in separate numerical models: (i) coupled friction heat gen eration; (ii) plastic flow slip zone development: and (iii) three-dimension al heat and material flow. The friction induced heat generation model was u sed to quantify the contributions of coupled thermomechanical friction heat ing, including non-linear interfacial phenomena between the tooling (e.g. s tir pin) and material being welded. The plastic work induced heating effect s were also examined. The plastic slip formation mechanisms were then inves tigated by considering contributions from various heating mechanisms. Final ly, a simplified three-dimensional heat and material flow model, based on t he observations from the coupled friction heat generation model, was used t o establish some initial insight regarding the heat and material flow. The results,from the three subproblem areas were then generalised in the form o f a simple parametric relationship between welding variables (i.e. travel a nd rotating speeds) and weld formation conditions. A series of assumptions were made in constructing these individual models since there exists little information on actual material behaviour under friction stir welding condi tions. However, the findings from the present study not only illuminate som e of the important weld formation mechanisms in friction stir welding, but also provide tin effective framework for more focused investigations into s ome of the fundamental phenomena identified in the three subproblem areas; such investigations will be reported separately in a future publication.