Modeling of ductile crack propagation in expanded thin-walled 6063-T5 aluminum tubes I. Barsoum n , F. Khan, A. Molki, A. Seibi Department of Mechanical Engineering, The Petroleum Institute, PO Box 2533, Abu Dhabi, United Arab Emirates article info Article history: Received 14 August 2013 Received in revised form 17 December 2013 Accepted 20 January 2014 Available online 30 January 2014 Keywords: Ductile failure Continuum damage model Tubular expansion Aluminum Oil and gas abstract In this paper the ductile failure behavior of mechanically expanded 6063-T5 aluminum tubes was studied experimentally and numerically. The expansion of the tubes was performed mechanically by using a conical mandrel with the objective to study the failure mode that governs the expansion process of this material. To localize the failure the tubes were drilled with circular holes. The fractured surfaces of failed expanded tubes were examined and revealed a flat ductile dimple rupture characteristic. A finite element model, which is based on continuum damage mechanics, is developed to mimic the experiments. The model also predicts ductile crack propagation and failure in the expanded tubes with embedded holes very well making it a suitable tool for studying the tubular expansion process and for optimizing the expansion tools. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction Solid expandable tubular technology (SETT) is an emerging technology in the oil and gas industry. SETT is a cold working process in which a conical mandrel of various diameters and shapes is pushed axially into the tube either mechanically or hydraulically to obtain the desired radial expansion ratio. The cold working process changes the shape of the cylindrical tube resulting in permanent radial expansion. This technology is being used to replace the traditional multi-diameter telescopic casing configura- tion used in oil wells with the SETT mono-diameter casing. This is achieved by expanding multiple tubes of a certain diameter in the well resulting in a rather uniform diameter throughout the well hole. This provides a larger downhole diameter than the conven- tional telescopic configuration, which results in an increased rate of oil production. Several studies related to SETT have been performed over the last two decades and proved its viability in field applica- tions [1–8]. During the expansion process it is important to maintain the mechanical integrity of the tube being expanded. The tubular material grades used should have sufficient strength and ductility to sustain the large radial expansion without failing during the expansion process due to the cold working process. Expansion of aluminum and steel tubes [9] showed that the failure mode is governed by ductile failure. Few studies have addressed ductile failure during expansion of tubes, which is important to control if one is to achieve a successful expansion process. Hence, it is desired to develop a modeling framework to model the tubular expansion process by accounting for ductile failure in order to prevent it while expanding the tubes. The underlying micro-mechanisms of the ductile failure process are nucleation, growth and coalescence of micro-void [10–13]. There are various ways of simulating ductile failure, as reported in the literature, with varying complexity. The Gurson-like models [14–17], which are based on porous dilatant plasticity, have been a common approach to model ductile failure. However, the short- comings of these models are that information about the micro- structure of the solid such as the initial void volume fracture is usually required as an input, which make them somewhat imprac- tical to use in engineering applications. In recent years continuum damage based models [18–21] has gained wide usage in modeling ductile failure rather than the void growth based Gurson-like models. The advantage here is that no microstructural information about the solid is required, however a failure envelope needs to be established based an equivalent failure strain as function of some parameters characterizing the stress state [12,13,22,23]. In this study a finite element modeling framework based on continuum damage mechanics is proposed to model the tubular expansion process and the ductile failure associated with it. The study focuses on the usage of Al 6063-T5 pipes, but the modeling framework could as well be applied to casings and pipes made of steel commonly used in the well completions in the oil and gas industry. The paper starts out by outlining the procedure for experimentally establishing the stress–strain curve and the failure Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ijmecsci International Journal of Mechanical Sciences 0020-7403/$ - see front matter & 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijmecsci.2014.01.012 n Corresponding author. Tel.: þ97 155 800 6641. E-mail addresses: imad@b-e-c.se, ibarsoum@pi.ac.ae (I. Barsoum). International Journal of Mechanical Sciences 80 (2014) 160–168