The Effects of Specimen Geometry on the Accuracy of Tensile Testing of Metallic Superplastic Materials Fadi Abu-Farha 1, a , Mohammed Nazzal 2,b and Richard Curtis 3,c 1 Department of Mechanical Engineering, Penn State Erie, Erie, PA 16510, USA 2 School of Technological Sciences, German Jordanian University, Amman, Jordan 3 King’s College Dental Institute, Guy’s Tower, King’s College London, London, UK a fka10@psu.edu, b mohammad.nazzal@gju.edu.jo, c richard.curtis@kcl.ac.uk Keywords: Superplastic Materials, Tensile Testing, Specimen Geometry, Material Flow. Abstract. This work investigates the sensitivity of a superplastic material’s tensile test to the major geometrical parameters of the selected test specimen. This required generating a large number of specimens by systematically varying the gauge length, gauge width, grip length and width of a standard geometry. The specimens were prepared from a moderately superplastic AZ31B-H24 magnesium alloy sheet and were then stretched at a selected rate and temperature. Deformation in each specimen was tracked via an electrochemically-etched fine grid which was particularly used to quantify the amount of material flow from the grip into the gauge region. The consequences of the latter on the accuracy of measured stresses and strains were correlated back to the corresponding geometrical parameters. Ultimately, the results were utilized to set the guidelines for selecting the optimum parameters in a “proper” specimen, for testing the unique class of superplastic materials. Introduction When reviewing the efforts on tensile testing of superplastic materials, one needs not to look for long before realizing the discrepancies in the test specimens adopted by the various researchers. For a long time, this could have been blamed on the lack of a specialized standard that specifies the proper specimen geometry, and teaches the proper procedure for testing these materials. But this is not the case anymore, since three standards have been introduced within the past decade [1-3]. Unhappily, these standards do not agree on several issues including the size and dimensions of the proposed test specimens. Additionally, they do not explain how those geometries were arrived at and whether they were optimized for accurate testing results. Perhaps that’s why we still come across efforts with specimens that do not conform to any of the standard ones. This issue is problematic from different perspectives. The fact that superplastic materials are tested at elevated temperatures does not allow the use of extensometers making strain measurements entirely dependent on the specimen geometry and the way a gauge length is defined. Also, with the lack of a standard specimen, it is likely to challenge the accuracy of claims of extreme superplastic elongations, particularly those exceeding 5000% [4]. More importantly, it is rather hard to compare or cross-use the data produced by various investigators, even for the same materials. This has provoked several efforts on trying to understand the influence of specimen geometry on the tensile test. Bate et al. [4], for instance, focused on studying the effects of the gauge length-to-width ratio. Johnson et al. [5] investigated material flow and its effects on strain rate non-uniformity along the gauge length of the specimen. Both suggest a large gauge length-to-width ratio to minimize test errors. In this work, we complement such efforts by attempting a comprehensive experimental investigation on the effects of four geometrical parameters; namely gauge length, width, grip length and width. The impact of varying each parameter on the test specimen’s deformation is evaluated in the gauge region as well as the grip region and the outcome is correlated to the accuracy of the measured stresses and strains. It is hoped that the results would promote discussions on developing a universally-accepted specimen geometry for the tensile testing of superplastic materials. Key Engineering Materials Vol. 433 (2010) pp 325-331 © (2010) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/KEM.433.325 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 the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 128.118.38.44-14/12/09,15:50:02)