Numerical–experimental crack growth analysis in AA2024-T3 FSWed butt joints Roberto Citarella, Pierpaolo Carlone ⇑ , Marcello Lepore, Gaetano S. Palazzo Department of Industrial Engineering, University of Salerno, Via Giovanni Paolo II, 132, 84084 Fisciano (SA), Italy article info Article history: Available online 18 October 2014 Keywords: Friction stir welding Residual stress Contour method Crack growth Two parameter crack growth law FEM DBEM abstract This paper deals with a numerical and experimental investigation on the influence of residual stresses on fatigue crack growth in AA2024-T3 friction stir welded butt joints. The computational approach is based on the sequential usage of the Finite Element Method (FEM) and the Dual Boundary Element Method (DBEM). Linear elastic FE simulations are performed to evaluate the process induced residual stresses, by means of the contour method. The computed stress field is transferred to a DBEM environment and superimposed to the stress field produced by a remote fatigue traction load applied on a friction stir welded cracked specimen; the crack propagation is then simulated according to a two-parameter growth model. Numerical results have been compared with experimental data showing good agreement and evi- dencing the predictive capability of the proposed method. The obtained results highlight the influence of the residual stress distribution on crack growth. Ó 2014 Civil-Comp Ltd and Elsevier Ltd. All rights reserved. 1. Introduction Friction stir welding (FSW) is an innovative joining technique patented by The Welding Institute of Cambridge in 1991. Following the early successful applications in aluminum welding, FSW has been applied to other engineering materials, such as copper, steel, titanium, and metal matrix composites. Conceptually, the FSW process is quite simple: a non-consumable rotating tool, consti- tuted by a shoulder and a pin, is plunged between the adjoining edges of the parts to be welded and moved along the desired weld line. The tool–material dynamic interactions locally increase the work piece temperature, due to frictional as well as viscous dissipations. The induced softening allows the processing material to flow around the pin, from the front (leading edge) to the rear (trailing edge) according to complex patterns, resulting in a solid state weld [1–3]. In recent years FSW received a great deal of attention from the scientific as well as industrial community, due to several remark- able advantages with respect to more traditional fusion welding processes, mainly connected to solid state welds provided. Indeed, the poor dendritic microstructure, the high porosity in the weld zone, the severe residual stress distributions induced by material melting in conventional techniques strongly reduce the mechani- cal behavior of the assembly. On the contrary, during FSW, the adjoining material is heated below the melting temperature and, as a consequence, all phase transformations happen at the solid state. This feature makes the FSW process very promising in join- ing difficult-to-weld materials, such as medium to high strength aluminum alloys (2xxx, 6xxx, and 7xxx series), currently consid- ered of great interest in the transport industries. More specifically, for aeronautical applications, the precipita- tion hardenable AA2024 (Al–Cu) alloy is gaining considerable attention, for instance for the realization of nose barrier beam or fuselage panels [4–6]. What is more, the reduction of production costs and weight and the increase of strength and damage toler- ance with respect to riveted lap joints make FSW a very attractive process to aerospace industry. A wider implementation of the technique in safety–critical components, however, requires a deeper understanding of static strength as well as of fatigue behavior of FSWed assemblies. It is generally accepted that the aforementioned properties mainly rely on residual stress and, for a minor extent on microstructure and microhardness. Even if FSW residual stresses are generally lower if compared to conventional welding processes [7], an accurate knowledge of FSW residual stress distributions is crucial to inves- tigate buckling behavior [8–9] as well as crack growth and fatigue response [10–15] of welded assemblies. In this sense some results have already been presented in the inherent literature, relatively, for instance, to AA6082-T6 and AA6061-T6 [10], AA6063-T6 [11], AA2024-T351 [12,13], AA6005C [14], and AA2915 [15] FSW joints. The slower crack propagation in FSWed material with respect to http://dx.doi.org/10.1016/j.advengsoft.2014.09.018 0965-9978/Ó 2014 Civil-Comp Ltd and Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: pcarlone@unisa.it (P. Carlone). Advances in Engineering Software 80 (2015) 47–57 Contents lists available at ScienceDirect Advances in Engineering Software journal homepage: www.elsevier.com/locate/advengsoft