ORIGINAL PAPER Simulation of thermal behavior during friction stir welding process for predicting residual stresses Christian Dresbach • Marinus J. van Enkhuizen • Ulises Alfaro Mercado • Stefan Reh Received: 12 December 2013 / Revised: 7 October 2014 / Accepted: 17 December 2014 Ó Deutsches Zentrum fu ¨r Luft- und Raumfahrt e.V. 2014 Abstract Using a transient thermal finite element ana- lysis, the thermal behavior during friction stir welding (FSW) of aluminum sheets for aerospace applications was calculated. The thermal behavior during the FSW process is of interest for all aspects of distortion engineering or microstructural interpretations for material design. In the presented approach to determine the amount of deforma- tion caused by the thermal residual stresses only, the measured temperature history of the welding tool, the thermomechanical material properties and the thermal contact properties have to be known. Since the calculated time-dependent temperature distribution agrees very well with experimentally measured temperatures at seven dif- ferent locations during a FSW experiment, it is concluded that the model accurately predicts the thermal history during welding. In addition, a first attempt to calculate the distortion, due to thermal residual stresses, is presented and compared to experimentally measured distortion. Although the calculated values of the distortion are too low compared to experimental results, the approach gives a first impres- sion on the origin of the distortion and will be pursued in further investigations. Keywords FSW  Simulation  Distortion 1 Introduction Friction stir welding (FSW) enhanced during the last years from a scientific research field to a very interesting upcoming production technology. Consequently, there are many attempts for up-scaling the process to weld large industrial components. Especially, when building primary structures of airplanes, it is necessary to consider and minimize the production tolerances as well as the distor- tions resulting from the welding process. During the FSW process, two metal sheets are placed directly against each other and fixed using special blank holders. A rotating tool is pressed on the contact region between both sheets. Due to a local frictional heating of the tool and the welding sheets, the material locally softens so that the tool can be pressed into the sheets and moved through the contact line. The softened material is extruded by the rotating and transverse motion of the tool, so that a permanent con- junction between the sheets is build without a local melting of the material. A principle sketch of the friction stir welding process is shown in Fig. 1. A detailed description of the friction stir welding process and the state of the art in FSW can be found in [1, 2]. Despite the advantages of this welding method, the thermomechanical process and the influence on the residual stresses are not completely understood. Simulation of the FSW process is therefore a key to gain insight into the thermomechanical process and its impact on the residual stresses. To achieve this goal, different models have been proposed in the literature: Chen et al. developed a model to predict the thermal history and the subsequent thermal stresses with involving the mechanical effect of the tool [3]. Difficulties are present within this model to determine the generated heat adequately. Khandkar et al. use a two- step model to determine the thermal residual stresses and This paper is based on a presentation at the German Aerospace Congress, September 10–12, 2013, Stuttgart, Germany. C. Dresbach (&)  M. J. van Enkhuizen  U. Alfaro Mercado  S. Reh German Aerospace Center, Institute of Materials Research, Linder Hoehe, 51147 Cologne, Germany e-mail: christian.dresbach@dlr.de 123 CEAS Aeronaut J DOI 10.1007/s13272-014-0145-9