Editing Shape-memory alloy (section)

=== Response time and response symmetry ===
SMA actuators are typically actuated electrically, where an electric current results in [[Joule heating]]. Deactivation typically occurs by free convective heat transfer to the ambient environment. Consequently, SMA actuation is typically asymmetric, with a relatively fast actuation time and a slow deactuation time. A number of methods have been proposed to reduce SMA deactivation time, including forced convection,<ref>{{cite journal|last=Lara-Quintanilla|first=A.|author2=Hulskamp, A. W. |author3=Bersee, H. E. |title=A high-rate shape memory alloy actuator for aerodynamic load control on wind turbines|journal=Journal of Intelligent Material Systems and Structures|date=October 2013|volume=24|issue=15|pages=1834–1845|doi=10.1177/1045389X13478271|s2cid=110098888|url=http://resolver.tudelft.nl/uuid:a7be07c6-81b2-4486-a993-72a2da24644f}}</ref> and lagging the SMA with a conductive material in order to manipulate the heat transfer rate.

Novel methods to enhance the feasibility of SMA actuators include the use of a conductive "[[Thermal insulation|lagging]]". this method uses a thermal paste to rapidly transfer heat from the SMA by conduction. This heat is then more readily transferred to the environment by convection as the outer radii (and heat transfer area) are significantly greater than for the bare wire. This method results in a significant reduction in deactivation time and a symmetric activation profile. As a consequence of the increased [[heat transfer]] rate, the required current to achieve a given actuation force is increased.<ref>{{cite journal |last1=Huang|first1=S|last2=Leary|first2=Martin|last3=Attalla|first3=Tamer|last4=Probst|first4=K| last5=Subic |first5=A |title=Optimisation of Ni–Ti shape memory alloy response time by transient heat transfer analysis |journal=Materials & Design |volume=35|pages=655–663|year=2012|doi=10.1016/j.matdes.2011.09.043}}</ref>

[[File:Comparative force-time response of bare and lagged Ni-Ti shape memory alloy.png|thumb|center|upright=3|Comparative force-time response of bare and lagged Ni-Ti shape memory alloy.<ref>{{cite journal|last1=Leary|first1=M|last2=Schiavone|first2=F|last3=Subic|first3=A|title=Lagging for control of shape memory alloy actuator response time |journal=Materials & Design |volume=31 |pages=2124–2128 |year=2010 |doi=10.1016/j.matdes.2009.10.010 |issue=4}}</ref>]]