Stress concentration effects of undercut defect and reinforcement metal in butt welded joint M. Cerit, O. Kokumer, K. Genel * Mechanical Engineering Department, Sakarya University, Adapazari 54187, Turkey article info Article history: Received 8 July 2009 Accepted 11 October 2009 Available online 1 November 2009 Keywords: Welding Defect Stress concentration Finite element abstract In the present study, stress distribution of butt welded joints with various amounts of rein- forcement metal and undercut defect has been investigated under uniaxial tension for a full penetration by systematically conducting a series of two-dimensional finite element (FE) models. The FE analysis indicated that the amount of reinforcement metal in weld zone has an important effect on stress distribution. For 120° of the reinforcement angle that designating reinforcement metal in weld joint, and 0.5 mm of toe radius, the value of stress concentration factor (SCF) exceeds 3.3r 0 . The analyses show that SCF takes much higher values in both low reinforcement angle and ratio of toe radius to plate thickness (R/ t). As for joints with undercut defects, it is concluded that severity of SCF is mainly con- trolled by the ratio of depth to radius of undercut (h/r) and width (W). In addition to under- cut defect, the presence of reinforcement metal, SCF noticeably increases with decreasing the reinforcement angle; it attains maximum value (7.4r 0 ) for h/r = 5 and W = 3 mm. How- ever, for the joints having wider undercut defects, the influence of reinforcement metal on SCF is found to be relatively lower; SCF is 6.7r 0 for W = 6 mm. Finally, an attempt has been made to construct simple relationships among the SCF of the weld joint, reinforcement angle, undercut defect and dimensionless parameters defining weld toe detail. Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. 1. Introduction It is well known that butt weld is an important connection for the integrity of most types of welded structures such as bridges, ships, pressure vessels and offshore platforms. The mechanical properties of a welded joint depend mainly on micro- structure of heat affected zone (HAZ), residual tensile stress and geometrical discontinuities such as misalignment, excessive reinforcement metal, toe radius and undercut defect [1]. These geometrical discontinuities formed on the welded joint tend to intensify the local stress field and hence reduce the load carrying capacity, which consequently represent an important limitation to the safe and reliable of welded structures. The magnification of the stress at the local stress field can be ex- pressed by the elastic stress concentration factor, K t (SCF), which must be known in engineering analysis and design. The undercut defect, associated with either improper welding techniques or excessive welding currents, or both, is generally lo- cated parallel to junction of weld metal and base metal at the toe or root of the weld [1,2]. The weld toe region is the point at which the base metal and weld face meet, and the greatest changes occur in their section. For the cyclic loading, the stage of crack initiation is dramatically reduced by the sharp toe radius and possible presence of undercut defect [3]. Therefore, there is practically no crack initiation period due to these discontinuities, which behave as pre-existing cracks. As a result, the fa- tigue life of a welded joint is much lower than that of the base metal. From the experimental studies and failure analyses on 1350-6307/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.engfailanal.2009.10.010 * Corresponding author. Tel.: +90 264 295 5860; fax: +90 264 295 5601. E-mail address: kgenel@sakarya.edu.tr (K. Genel). Engineering Failure Analysis 17 (2010) 571–578 Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal