HYPERELASTIC MATERIAL MODELS FOR SWELLING ELASTOMERS: EXPERIMENTAL AND NUMERICAL INVESTIGATION M. Akhtar * , S.Z. Qamar, T. Pervez, R. Khan and M.S.M. Al-Kharousi Department of Mechanical and Industrial Engineering, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al Khod 123, Sultanate of Oman * Corresponding author. Tel. +968-24142669; Fax +968-24141316 E-mail address: maazakhtar@hotmail.com (Maaz Akhtar) ABSTRACT Elastomers are rubber-type materials that can be stretched to several times their initial length. A relatively new type, swellable elastomers can swell when in contact with certain fluids (water, oil, or acid), thereby altering the material properties. The authors are working on modeling and simulation of swelling elastomers used in petroleum applications. However, very little data is openly available about material properties and swelling response of these new elastomers. An elaborate experimental setup has therefore been designed to investigate the material behavior of these elastomers, so that they can be efficiently utilized in the field. As a part of this study, the current work focuses on experimental and numerical investigation of the tensile behavior of two swelling elastomers. No evaluation of material models for swelling elastomers can be currently found in published literature, thus the need for the current work. Tests are carried out using ring samples in accordance with ASTM-D412 standard test method. Tensile tests are then simulated, using the commercial finite element package ABAQUS. Treating swelling elastomers as a type of hyperelastic material, simulations are done using material models of this kind available in the ABAQUS library. Material coefficients for each model (Ogden, Yeoh, Arruda-Boyce) are determined using the efficient fitting procedure of ABAQUS. Models are compared with each other for tensile behavior in both un-swelled and swelled conditions. All three models yield close results for one elastomer type. However, Ogden model appears to give the overall best results for tensile behavior of the two elastomers under swelled and unswelled states. Keywords: Swelling elastomers; Tensile testing; Hyperelastic material models; Finite element analysis 1. INTRODUCTION Elastomeric materials have a variety of applications in fields such as automotives, vibration dampers, medical instruments, structural members, and especially as sealing elements in petroleum and other industries. In oilfield development, inert elastomer seals have been used for quite some time, but the advent of swelling elastomer seals has revolutionized the technology. Swelling elastomers are a special type of elastomers that swell when they interact with fluids like saline water or oil. Swelling results in change of volume, thickness, density, hardness and other material properties, as discussed in Qamar et al. [1]. In water swelling elastomers, swelling rate depends on temperature and salinity of water, higher amount of swelling observed in less saline water and at higher temperatures. Water-swelling elastomers swell through absorption of saline water (osmosis), while oil-swelling elastomers swell through absorption of hydrocarbons (diffusion) [2]. Some of the notable applications of swelling elastomers in petroleum development are zonal isolation, alternative to cementing, and well completion in oilfileds where cement jobs are difficult. Before using swelling elastomers for any application, behaviour under different fluids and environmental conditions should be known to predict the exact response. It is difficult, costly, and time-consuming to perform experiments for all conditions. A robust numerical simulation strategy, validated against experimental results, can be used to predict the behavior of elastomers. Before developing an FEM model of elastomer seal performance, a thorough evaluation should be carried out to decide which material model is most suitable for swelling elastomers. Such a comparative evaluation of material models for  MATERIALS AND MANUFACTURING