Title: Axial-torsion behavior of superelastic tubes: Part I, proportional isothermal experiments

Abstract

The tensile response of superelastic shape memory alloys (SMAs) has been widely researched, but detailed experimental studies under multi-axial loading are relatively rare. In Part I, we introduce the isothermal responses of commercially-available superelastic NiTi tubes for a series of proportional stretch-twist controlled histories, spanning pure tension to simple torsion to pure compression. These axial-shear responses are used to quantify the onset and saturation during forward (loading) and reverse (unloading) stress-induced transformations for the first time. Each of the four transformation surfaces is well-captured by a smooth (three-parameter) ellipse in both strain and stress space. A simple Gibbs free energy model is presented to show how the driving force for phase transformation is approximately constant across all proportional strain paths and how the stress and strain transformation surfaces are conjugate to one another. In addition, transformation kinetics and surface strain morphologies are characterized by stereo digital image correlation (DIC). Under extension at low amounts of twist, stress-induced transformation involves strain localization in helical bands that evolve into axial propagation of ring-like transformation fronts with fine criss-crossing fingers (similar to those seen by Q. P. Sun and co-workers in pure extension). Yet, at large amounts of twist, including simple torsion andmore » pure torsion, we report a new transformation morphology, involving strain localization along nearly longitudinal bands in the tube. The sequel (Part II) will address the response to non-proportional stretch-twist paths. Together, these detailed multi-axial results advance the scientific understanding of superelasticity and inform efforts to develop high-fidelity SMA constitutive models and simulation tools.« less

Authors:

Reedlunn, Benjamin; LePage, William S. ;

• Search DOE PAGES for author "LePage, William S."
• Search DOE PAGES for ORCID "0000-0002-6811-3162"

Daly, Samantha H. ;

• Search DOE PAGES for author "Daly, Samantha H."
• Search DOE PAGES for ORCID "0000-0002-7297-1696"

Shaw, John A.

Publication Date:

Sat Aug 01 00:00:00 EDT 2020

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES); National Science Foundation (NSF); UM/General Motors

OSTI Identifier:

1881358

Alternate Identifier(s):

OSTI ID: 1617827; OSTI ID: 1618100; OSTI ID: 1619230; OSTI ID: 1619827

Report Number(s):

SAND2020-3638J; SAND2019-4077J; SAND-2020-3638J
Journal ID: ISSN 0020-7683; S0020768320301062; PII: S0020768320301062

Grant/Contract Number:  

SC0003996; CMMI 1251891; AC04-94AL85000; 1251891

Resource Type:

Published Article

Journal Name:

International Journal of Solids and Structures

Additional Journal Information:

Journal Name: International Journal of Solids and Structures Journal Volume: 199 Journal Issue: C; Journal ID: ISSN 0020-7683

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 42 ENGINEERING; shape memory alloy; NiTi; Nitinol; superelasticity; phase transformation; multi-axial testing; constitutive behavior