Coupled stress-strain and electrical resistivity measurements on copper based shape memory single crystals

Cezar Henrique Gonzalez,Carlos José De Araújo,Ney Freitas De Quadros,Michel Morin,Gerard Guénin

doi:10.1590/s1516-14392004000200014

Abstract

Recently, electrical resistivity (ER) measurements have been done during some thermomechanical tests in copper based shape memory alloys (SMA's). In this work, single crystals of Cu-based SMA's have been studied at different temperatures to analyse the relationship between stress (s) and ER changes as a function of the strain (e). A good consistency between ER change values is observed in different experiments: thermal martensitic transformation, stress induced martensitic transformation and stress induced reorientation of martensite variants. During stress induced martensitic transformation (superelastic behaviour) and stress induced reorientation of martensite variants, a linear relationship is obtained between ER and strain as well as the absence of hys teresis. In conclusion, the present results show a direct evidence of martensite electrical resistivity anisotropy.

Highlights

IntroductionShape memory alloys (SMA’s) present different phenomena (one way shape memory effect, two way shape memory effect, superelasticity and rubber-like behaviour) which can be induced by changes in temperature and/or mechanical stress
Shape memory alloys (SMA’s) present different phenomena which can be induced by changes in temperature and/or mechanical stress
The value of this sum is close to the variation of resistivity corresponding to operation C, where a single variant of martensite is directly stress induced from a single crystal of austenite

Summary

Introduction

Shape memory alloys (SMA’s) present different phenomena (one way shape memory effect, two way shape memory effect, superelasticity and rubber-like behaviour) which can be induced by changes in temperature and/or mechanical stress. All those effects are characterised by modifications in crystalline structure of the SMA. Its main application is for determination of transformation temperatures, due to the susceptibility of ER to detect modifications in the crystalline structure of the SMA undergoing phase transformation during heating and cooling[1,2]. ER is used to measure the evolution of shape memory effect during ageing in parent phase and low temperature phase (martensitic stabilisation)[3,4,5,6]. It can be used to drive the material performance from electronic control

Methods

Results

Conclusion