Friction Stir Welding Process Parameter Effects on Workpiece Warpage due to Residual Strains

ABSTRACT An important performance measure of the quality of a weldis the permanent deformation developed during welding pro-cesses due to the thermally activated residual strains. This paperpresents the results of a sensitivity analysis that determines theeffects of processing parameters -such as the speed of rotationand the traveling speed of a rotating friction stir welding (FSW)tool- on the resulting residual strain fields. The problem has beenmodeled as a thermostructurally coupled problem via Finite El-ement Analysis of an elastoplastic workpiece under the influenceof heat generated from the stirring process and taking into ac-count the temperature dependent yield strength of the material.Results are presented and discussed in the context of our futureplans. INTRODUCTION Our work in the present paper is motivated by both short andlong term goals. The main short term goal is related to exploitingthe opportunities offered by the benefits of Friction Stir Weld-ing (FSW) as a specific joining technology. The long term goalis related to designing material and structural systems based onapplication driven requirements as defined from multiple stakeholders.Specifically, in terms of the long term goal, during the last 3years, we have embarked on a basic research program for devel-oping a framework capable of linking performance and process-ing specification data with fundamental material parameters andmodels that can efficiently capture the behavior of complex ma-terial systems [1]. The anticipated payoff of achieving this goalis the potential for facilitating the development of technologiesenabling rapid, low cost, optimally targeted, multiscalar mate-rial identification, design, processing, prototyping, manufactur-ing, certification and qualification, which are tailored to satisfyutility requirements defined from multiple perspectives associ-ated with various stakeholders. These types of requirements canbe functional, economic, maintenance and repair related, as wellas platform-life extension related. One of the application areaswe have targeted for demonstrating this framework is FSW-basedjoining of materials, due to its potential impact for marine andaerospace applications related to the naval missions and goals.Exploiting this very specific potential constitutes our short termgoal.However, prior to applying the principles and technologydeveloped by this framework it is necessary that we establish aquantitative relationship between performance characteristics ofFSW and the processing parameters involved in the FSW pro-cess. For this purpose we need to develop both a forward and aninverse modeling infrastructure for modeling and simulating theFSW aspects linking its utility and performance to the parame-ters involved in controlling the process. Having this infrastruc-ture enables the quantification of these associations.1This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States.Approved for public release; distribution is unlimited.