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Title: Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes

Abstract

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C is compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclicmore » mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less

Authors:
 [1];  [2];  [2];  [3];  [3];  [1]
  1. Brown Univ., Providence, RI (United States). School of Engineering
  2. Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Engineering
  3. Core Technologies, Minneapolis, MN (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1394986
Report Number(s):
LA-UR-17-26380
Journal ID: ISSN 1359-6454
Grant/Contract Number:
AC52-06NA25396; SC0008274
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 136; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Cyclic deformation; Shape memory alloys; Micropillars; Texture; Nanocrystalline

Citation Formats

Ghassemi-Armaki, Hassan, Leff, Asher C., Taheri, Mitra L., Dahal, J., Kamarajugadda, M., and Kumar, K. Sharvan. Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes. United States: N. p., 2017. Web. doi:10.1016/j.actamat.2017.06.043.
Ghassemi-Armaki, Hassan, Leff, Asher C., Taheri, Mitra L., Dahal, J., Kamarajugadda, M., & Kumar, K. Sharvan. Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes. United States. doi:10.1016/j.actamat.2017.06.043.
Ghassemi-Armaki, Hassan, Leff, Asher C., Taheri, Mitra L., Dahal, J., Kamarajugadda, M., and Kumar, K. Sharvan. 2017. "Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes". United States. doi:10.1016/j.actamat.2017.06.043.
@article{osti_1394986,
title = {Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes},
author = {Ghassemi-Armaki, Hassan and Leff, Asher C. and Taheri, Mitra L. and Dahal, J. and Kamarajugadda, M. and Kumar, K. Sharvan},
abstractNote = {Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C is compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.},
doi = {10.1016/j.actamat.2017.06.043},
journal = {Acta Materialia},
number = C,
volume = 136,
place = {United States},
year = 2017,
month = 6
}

Journal Article:
Free Publicly Available Full Text
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  • This paper continues the investigation of the elastic-plastic response of thin-walled tubes subjected to combined axial and torsional loads. The stress-strain loop under arbitrary variable loading is first discussed. It is then shown that due to the kinematic hardening, a steady state, either one of the reversed plasticity or one of the elastic shakedown, can always be reached under cyclic loadings, with a hysteresis loop in the form of a parallelogram or a straight line. As a result, the difference in response between nonproportional and proportional loading will finally disappear. The investigation indicates that the simple kinematic hardening rule ismore » able to describe, at least qualitatively, certain basic characteristics of the material behavior observed in nonproportional tests.« less
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  • Experimental results have shown that, during mechanical cycling under tension-compression load within {+-}4% strains, the NiTi shape memory alloy is cyclic strain-hardened. The maximum stresses under both tension and compression increase with increasing number of cycles and tend to stabilize with further cycling. The present work is focused on the martensite microstructure developed as a result of mechanical cycling. TEM observations show that, before cycling, the martensite variants are well self-accommodated to each other with the <011> type II twinning as the main lattice invariant shear. After mechanical cycling, the martensite plates are still self-accommodated and the (11{bar 1}) typemore » I twinning is most frequently observed. In addition to the stress-induced re-orientation of martensite and twin boundary movement within the martensite plate, various lattice defects have been developed both in the junction plane areas of martensite plates and within the martensite twins.« less
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