Editing Shape-memory alloy (section)

=== Structural fatigue and functional fatigue ===
SMA is subject to structural fatigue – a failure mode by which cyclic loading results in the initiation and propagation of a crack that eventually results in catastrophic loss of function by fracture. The physics behind this fatigue mode is accumulation of microstructural damage during cyclic loading. This failure mode is observed in most engineering materials, not just SMAs.

SMAs are also subject to functional fatigue, a failure mode not typical of most engineering materials, whereby the SMA does not fail structurally but loses its shape-memory/superelastic characteristics over time. As a result of cyclic loading (both mechanical and thermal), the material loses its ability to undergo a reversible phase transformation. For example, the working displacement in an actuator  decreases with increasing cycle numbers. The physics behind this is gradual change in microstructure—more specifically, the buildup of accommodation slip [[dislocations]]. This is often accompanied by a significant change in transformation temperatures.<ref name=Miyazaki>{{Cite journal | doi = 10.1016/j.msea.2006.02.054| title = Development and characterization of Ni-free Ti-base shape memory and superelastic alloys| journal = Materials Science and Engineering: A| volume = 438–440| pages = 18–24| year = 2006| last1 = Miyazaki | first1 = S.| last2 = Kim | first2 = H. Y. | last3 = Hosoda | first3 = H.}}</ref> Design of SMA actuators may also influence both structural and functional fatigue of SMA, such as the pulley configurations in SMA-Pulley system.<ref name=JMJ>{{Cite journal | doi = 10.1088/0964-1726/25/5/057001| title = Fatigue of NiTi SMA-pulley system using Taguchi and ANOVA| journal = Smart Materials and Structures| volume = 25| issue = 5| pages = 057001| year = 2016| last1 = M. Jani | first1 = J.| last2 = Leary | first2 = M. | last3 = Subic | first3 = A.| bibcode = 2016SMaS...25e7001M| s2cid = 138542543}}</ref>