Assessment of Crack Growth from a Cold Worked Hole by Coupled FEM-DBEM Approach R. Citarella, G. Cricrì, M. Lepore, M. Perrella Università degli Studi di Salerno – Dept. of Industrial Engineering, Via Giovanni Paolo II, 84084 Fisciano (SA), e-mail: rcitarella@unisa.it, gcricri@unisa.it Keywords: 3D crack growth, two parameter crack growth model, FEM-DBEM, residual stresses. Abstract. The main objective of the present work is the study of the effect of residual stresses, induced by a cold working split sleeve process, on the fatigue life of a holed specimen. The crack propagation is simulated by a two-parameters crack growth model, based on the usage of two threshold material parameters (∆K th and K max,th ) and on the allowance for residual stresses, introduced on the crack faces by material plastic deformations. The coupled usage of Finite Element Method (FEM) and Dual Boundary Element Method (DBEM) is proposed to simulate the crack propagation, in order to take advantage of the main capabilities of the two methods. The procedure is validated by comparison with experimental results (crack growth rates and crack path) available from literature, in order to assess its capability to predict the crack growth retardation phenomena. Introduction The cold working process applied to fastener holes introduces a compressive stress field around the hole reducing the tendency for fatigue cracks to initiate and grow under cyclic mechanical loading, consequently, for the accurate assessment of fatigue life a detailed knowledge of the residual stress profile is mandatory. One experimental technique available to measure the residual stresses is based on X-ray, even if, using the X-ray technique inevitably the resolution is limited being the stresses averaged over the irradiated volume; therefore it is not possible to resolve the steep stress gradients in the vicinity of the hole, and the peak values predicted by Finite Element simulation can result underestimated [1]. The main objective of the present work is the study of the effect of residual stresses induced by a cold working process on the fatigue life of structural engineering components; in this particular case specimens of simple geometry which are often used in the study of aircraft structures [2]. A 3D elastic-plastic FE (Finite Element) analyses simulates the cold working process [1] and provides the residual stress profile met by a propagating 3D crack originating from the cold worked fastener hole. The through the thickness propagation of a part through crack, initiated from the aforementioned hole is simulated by a two-parameters crack growth model [3], based on the usage of two threshold material parameters (∆K th and K max,th ) and on the allowance for residual stresses [4], introduced on the crack faces by material plastic deformations. The coupled usage of Finite Element Method (FEM) and Dual Boundary Element Method (DBEM) [3-4] is proposed to simulate the crack propagation, in order to take advantage of the main capabilities of the two methods (other possible approaches to simulate the residual stress effect in 2024 alloys coupled with crack propagation can be based on damage mechanics [5]). The procedure is validated by comparison with experimental results (crack growth rates and crack path) available from the literature [2, 6], in order to assess its capability to predict the crack growth retardation phenomena, introduced by the cold working process on a simple specimen, made of Al alloy 2024 T3-Alclad (LT), by a split sleeve process (Fig. 1). The study of crack propagation is demanded to the DBEM approach: in an integrated virtual environment, the previously calculated residual stresses are automatically transferred to a DBEM model of the holed plate and applied on the crack faces during the propagation. The Stress Intensity Factors (SIF's) are evaluated by the J-integral approach and the crack path is determined by the Minimum Strain Energy Density (MSED) criterion [7]. The aforementioned procedure presents non negligible advantages, with particular reference to the simplicity of the crack growth law calibration (few constant amplitude tests are sufficient without Key Engineering Materials Vols. 577-578 (2014) pp 669-672 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.577-578.669 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 79.26.12.105, University of Salerno, Fisciano (SA), Italy-11/08/13,22:42:14)