J. Phys. IV France
Volume 115, June 2004
Page(s) 185 - 194

J. Phys. IV France
115 (2004) 185
DOI: 10.1051/jp4:2004115023

Experimental study of torsion behaviour of NiTi alloy

P. Olier1, Ph. Matheron2 and J. Sicre3

1  Department of Elaboration and Control of Structure, Atomic Energy Commission (CEA), Saclay, France; CEA/DRT/LIST/DECS/SE2M, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
2  Department of Thermal Mechanics, Atomic Energy Commission (CEA), Saclay, France; CEA/DEN/DMT/SEMT/SRSI, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
3  Department of Spatial Technics, CNES/DTS/AE/MTE/ME, CNES Toulouse, 18 Av. Édouard Belin, 31401 Toulouse Cedex 4, France

The goal of this paper is to have a better understanding of the parameters which have an influence on torsional response of NiTi shape memory alloys (SMAs). The SMA investigated in this study was a titanium rich NiTi characterized by high transformation temperature (A $_{\rm s}$ of ~ 95 °C in fully annealed conditions). Resulting from post-forming annealing, two metallurgical conditions were achieved : restored conditions (470 °C-1 h) and recrystallised conditions (600 °C-1 h). The phase transformation temperatures and heat of transformation were measured for both conditions by differential scanning calorimetry. A first set of torsional tests were conducted in isothermal conditions for three different mechanical loading paths. The torque against the angular displacement was measured for each tested temperature. As a comparison, isothermal stress-strain curves obtained in tension and compression were reported which showing the influence of the solicitation mode on mechanical parameters (shear and young moduli, yield strength, critical strain and stress). The second set of tests is designed to measure the amplitude of shape memory effect and the recovery torque during heating. Thermomechanical experiments include the torsion response for thermal cycles under constant applied torque and for specimens deformed in martensitic phase and heated above A $_{\rm f}$ while their displacement was kept constant. The thermo-mechanical cycles were repeated at least three times for each specimen and for one of them the cycling effect (up to 50 cycles) was investigated. We found that the highest recovery torque and the largest level of strain recovery were obtained for restored conditions.

© EDP Sciences 2004