The issue of material performance over its designed life is of prime concern with designers lately due to increasing use of shape memory alloy (SMA) components in different engineering applications. In this work, a concept of "Driving force amplitude v/s no of cycles" is proposed to analyze functional degradation of SMA components under torsion. The model is formulated using experimentally measurable quantities such as torque and angle of twist with the inclusion of both mechanical and thermal loading in the same framework. Such an approach can potentially substitute the traditional fatigue theories like S-N, epsilon-N theories which primarily use mechanical loading effects with temperature being an external control parameter. Such traditional S-N, epsilon-N fatigue theories work well for capturing superelastic effects at a given temperature but not for shape memory effects or temperature dependent superelastic effects which involves mechanical and thermal coupling. Experiments on SMA extension springs are performed using a custom designed thermomechanical test rig capable of mimicking shape memory effect on thermally activated SMA springs held under constant deformation. For every thermomechanical cycle, load and temperature sensor readings are continually recorded as a function of time using LabVIEW software. The sensor data over the specimen lifetime is used to construct a "Driving force amplitude v/s no of cycles" relationship that can be used as a guideline for analyzing functional degradation of SMA components.

Date Published: 3 April 2013
PDF: 9 pages
Proc. SPIE 8689, Behavior and Mechanics of Multifunctional Materials and Composites 2013, 86890T (3 April 2013); doi: 10.1117/12.2014484

Published in SPIE Proceedings Vol. 8689:
Behavior and Mechanics of Multifunctional Materials and Composites 2013
Nakhiah C. Goulbourne; Hani E. Naguib, Editor(s)