Abstract
In spite of the rather complex and hysteretic behavior of SMA components (wires and springs), and the complex changes that occur in their microstructures, the preliminary design of SMA wires and springs turns out to be reasonably simple provided we utilize their shape memory characteristics in specific ways. Designing SMA actuators requires defining actuation intervals (temperature profile), load levels and/or displacement outputs over its intended designed life. The alloy composition dictates the transformation temperatures and the component’s operating range. SMA components could be functional under load controlled or displacement controlled or simultaneous load and displacement controlled setups.
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Notes
- 1.
In reality, this is the just the slope of the stress strain curve for the twinning deformation and is not really an elastic modulus.
- 2.
Note we do not use the spring constant at low temperature because the spring will be “plastic” at low temperature and we are designing it to be coil bound.
- 3.
Beware that many papers routinely ignore this and try to estimate the heat transfer coefficient using a simplified model. The answers, not surprising show wide divergence and indicate that the heat transfer coefficient varies during the process. Actually these papers are attributing the temperature stagnation due to phase transitions to variations in the heat transfer coefficient.
- 4.
This would be inappropriate for situations were repeated rapid cycling takes place as in the case of a heat engine or a flapping wing system or in vibration damping applications. For these systems it is important to consider the heating due to hysteresis also.
References
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Rao, A., Srinivasa, A.R., Reddy, J.N. (2015). Case Studies in the Preliminary Design of SMA Actuators. In: Design of Shape Memory Alloy (SMA) Actuators. SpringerBriefs in Applied Sciences and Technology(). Springer, Cham. https://doi.org/10.1007/978-3-319-03188-0_7
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DOI: https://doi.org/10.1007/978-3-319-03188-0_7
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