J. Phys. IV France 11 (2001) Pr8-339-Pr8-344
Reliability of resistance/deformation during electrically-driven thermal cycles under stress on Ni25Ti50Cu25 melt spun ribbonsG. Gomarasca1, G. Airoldi1 and A.V. Shelyakov2
1 INFM, Dipartimento di Scienza dei Materiali, Università di Milano Bicocca, Via R. Cozzi 53, 20125 Milano, Italy
2 Department of Solid State Physics, Moscow Engineering Physics Institute, Kashirskoe Shosse 31, 115409 Moscow, Russia
The use of shape memory alloys for sensing/actuating strictly relies on the possibility to easily relate the Electrical Resistance (ER) to strain (E). Previous measurements of ER vs ε on Ni25Ti50Cu25 ribbons detected during thermal cycling under a stress state have clearly shown that a linear relationship between ER and ε can be obtained for an applied stress lower than 50 MPa. ER and ε have been here investigated during repeated electrically driven thermal cycles under an applied stress either 50 or 100 MPa on Ni25Ti50Cu25 melt spun ribbons up to 8000 electrically-driven cycles. Small plastic deformation, with a typical figure of εp 5.10-4 for 50 MPa and εp 1.10-3 for 100 MPa, is built in during cycling and levels after few thousand cycles. Under a stress of 100 MPa specimens break after 2000-4000 cycles. No broken specimen has been found even after 8000 cycles under 50 MPa applied stress. The hysteresis width of the ER-ε curves modifies with cycling for both applied stresses.
© EDP Sciences 2001