Functional Fatigue of NiTi Shape Memory Wires under Assorted Loading Conditions

Abstract:

The rational design of shape memory alloy (SMA) actuators requires reliable data on the fatigue strength of the material under cyclic thermal activation (functional fatigue). Test results on SMAs under functional fatigue are scarce in the technical literature and the few data available are mainly limited to constant-stress loading. Since the SMA elements used within actuators are normally biased by elastic springs or by another SMA element, their stress state is far from constant in operation. The mismatch between actual working conditions and laboratory arrangements leads to suboptimal designs and undermines the prediction of the actuator lifetime. This paper aims at bridging the gap between experiment and reality. Four test procedures are planned, covering most of the typical situations occurring in practice: constant-stress, constant-strain, constant-stress with limited maximum strain and linear stress-strain variation. The paper describes the experimental apparatus specifically designed to implement the four loading conditions and presents fatigue results obtained from commercial NiTi wires tested under three of the four protocols.

• Periodical: Advances in Science and Technology (Volume 78)
• Pages: 40-45
• DOI: https://doi.org/10.4028/www.scientific.net/AST.78.40
• Online since: September 2012
• Authors: Giovanni Scire' Mammano, Eugenio Dragoni
• Keywords: Constant-Strain, Constant-Stress, Functional Fatigue, Limited Maximum Strain, Linear Stress-Strain Variation, SMA Wires

References

[1] I. Spinella, E. Dragoni, Design equations for binary shape memory actuators under dissipative forces. Proc Instn Mech Engrs, Part C: J. of Mechanical Engineering Science. 223 (2009) 531-543.

DOI: 10.1243/09544062jmes1232

[2] G. Eggeler, E. Hornbogen, A. Yawny, A. Heckmann, M. Wagner, Structural and functional fatigue of NiTi shape memory alloys. Materials Science and Engineering A. 378 (2004) 24–33.

DOI: 10.1016/j.msea.2003.10.327

[3] L. Fumagalli, F. Butera, A. Coda, SmartFlex NiTi Wires for Shape Memory Actuators. J. of Materials Engineering and Performance. 18 (2009) 691–696.

DOI: 10.1007/s11665-009-9407-9

[4] M. Mertmann, G. Vergani, Design and application of shape memory actuators. Eur. Phys. J. Special Topics 158 (2008) 221–230.

DOI: 10.1140/epjst/e2008-00679-9

[5] D.C. Lagoudas, D.A. Miller, L. Rong, P.K. Kumar, Thermomechanical fatigue of shape memory alloys. Smart Materials and Structures 18 (2009) 085021.

DOI: 10.1088/0964-1726/18/8/085021

[6] M. Mertmann, A. Bracke. E. Hornbogen, Influence of the thermal treatment on the stability of partially constrained recovery of NiTi Actuator wire. J. de physique IV C8 (1995) 1259-1264.

DOI: 10.1051/jp4/1995581259

[7] V. Demers, V. Brailovski, S.D. Prokoshkinb, K.E. Inaekyana, Thermomechanical fatigue of nanostructured Ti–Ni shape memory alloys. Materials Sci. and Eng. A. 513-514 (2009) 185-196.

DOI: 10.1016/j.msea.2009.01.055

[8] G. Scirè Mammano, E. Dragoni, Functional fatigue of shape memory wires under constant-stress and constant-strain loading conditions. Engineering Procedia 10 (2011) 3962-3707.

DOI: 10.1016/j.proeng.2011.04.607

[9] G. Scirè Mammano, E. Dragoni, Functional fatigue of Ni–Ti shape memory wires under various loading conditions. Int. J. fatigue (2012)

DOI: 10.1016/j.ijfatigue.2012.03.004

[10] H. Nakazawa, S. Kodama, Statistical S-N testing method with 14 specimens: JSME standard method for determination of S-N curves. Statistical research on fatigue and fracture (1987) 59–69.