Residual stress evaluation in friction stir-welded aluminum plates using finite element method and acoustic emission Ali Mahdian Ahi 1 , Jalal Yousefi 1, *, Mehdi Ahmadi Najafabadi 1 , Amir Esmaeilzare 1 , and Amir Refahi Oskouei 2 1 Mechanical Engineering Department, Amirkabir University of Technology, 424 Hafez Ave., Tehran 15875-4413, Iran 2 Department of Mechanical Engineering, Shahid Rajaee Teacher Training University, Lavizan, Tehran 1678815811, Iran Received: 27 July 2016 Accepted: 12 October 2016 Ó Springer Science+Business Media New York 2016 ABSTRACT Acoustic Emission (AE) method proposed in this paper as a novel approach was used to evaluate residual stress in friction stir welding (FSW) of 5086 aluminum plates. A finite element method was used to evaluate residual stresses in alu- minum plates caused by FSW, which was validated by the hole-drilling process. Moreover, fundamental antisymmetric Lamb wave mode (A 0 ) was implemented to measure the residual stresses produced by FSW process. The novelty of this investigation is the combination of a robust signal-processing analysis and theory of acoustoelastic Lamb wave. In this analysis, an envelope of A 0 mode is used instead of signal time of flight, which obliterates the need to utilize a synchronizing clock of receiving sensors. It was shown that the duration of the signal changes linearly with residual stress variation, and a new equation was then established. Finally, it is confirmed that AE as a nondestructive approach can be an efficient tool for residual stress measurement in welded plate. Introduction The aluminum components used in many industrial applications should have decent mechanical proper- ties in combination with lower residual stress levels. The residual stresses can affect some engineering properties of these structural components, such as fatigue life, deformation, dimensional stability, cor- rosion resistance, and brittle fracture. Residual stresses can be defined as ‘‘locked-in’’ stresses that exist in the structural components in the absence of any external loads [1]. These stresses can seriously shorten the component’s life and cause a brittle fracture. Considerable effort is currently allocated to the improvement of an efficient method for evalua- tion of residual stresses in industrial applications. Therefore, it is imperative to assess residual stresses effectively. One of the main sources of residual stress in the industry is a welding process, which occurs due to nonuniform thermal expansions and solidifications during this process. One of the most prevalent Address correspondence to E-mail: jalal.yousefi@aut.ac.ir DOI 10.1007/s10853-016-0498-z J Mater Sci