Mechanical Behavior of an Ni-Ti Shape Memory Alloy Under Axial-Torsional Proportional and Nonproportional Loading

[+] Author and Article Information
T. Jesse Lim, David L. McDowell

GWW School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405

J. Eng. Mater. Technol 121(1), 9-18 (Jan 01, 1999) (10 pages) doi:10.1115/1.2816007 History: Received February 17, 1998; Revised May 22, 1998; Online November 27, 2007


Several biaxial proportional and nonproportional loading experiments are reported for thin-wall tubes of a pseudoelastic Ni-Ti shape memory alloy (SMA). In addition to the mechanical behavior, temperature was measured during the experiments. It is shown that the phase transformation exhibits asymmetrical behavior in the case of tension-compression cycling. The transformation strain rate is determined for selected histories by numerical differentiation of data. Under nonproportional loading, the rate of phase transformation does not follow a generalized J2 -J3 criteria based on results of micromechanical simulations for proportional loading. The role of simultaneous forward and reverse transformations on the nonproportional transformation response is examined using a simple micromechanical model, and the direction of the inelastic strain rate is adequately predicted. Load- and strain-controlled experiments at different strain rates, with and without hold times, are reported and coupled thermomechanical effects are studied.

Copyright © 1999 by The American Society of Mechanical Engineers
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