Structural and functional fatigue of NiTi shape memory alloys

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…In NiTi SMAs fatigue can occur by two distinct modes: functional and structural fatigue [214]. In the former the functional properties of the material suffer a degradation during cyclic solicitation, while the latter the material fails, during high cyclic loads like any other engineering material.…”

“…It is, thus, evident that understanding the fatigue behaviour and the underlying microstructural processes is of great importance, in order to safely design NiTi components [214]. Microstructural features, such as grain size, are known to influence the fatigue strength of NiTi [215].…”

Investigation of TiNi shape memory alloy for thermosensitive wire drive

“…All functional properties of a TiNi alloy depend on the number of thermal-deformation cycles [14][15][16][17][18][19][20][21]. To determine this dependence for the given alloy, thermocycling of the wire samples under different stresses was conducted.…”

Functional fatigue recovery of superelastic cycled NiTi wires based on near 100 °C aging treatments

“…For classical materials such as steel, usually fatigue refers to structural fatigue, which means incapacity to support further loads and might end in fracture. In fact, fatigue of NiTi alloys has been extensively studied [10][11][12][13][14][15][16][17]. During the test or during the working life, the SMAs accumulate micro-structural defects and nano-scale precipitates which might induce significant modifications in functional properties, this can happen much before the structural failure.…”

“…During the test or during the working life, the SMAs accumulate micro-structural defects and nano-scale precipitates which might induce significant modifications in functional properties, this can happen much before the structural failure. We should then address also the problem of functional fatigue in SMA, as failure to perform the expected work or describe the expected stress-strain-temperature designed trajectories after a number of cycles [16]. The functional fatigue is very important in applications of SMA such as dampers with re-centring properties [3].…”