Effect of Intermittent Overload Cycles on Thermomechanical Fatigue Life of NiTi Shape Memory Alloy Wire

Influence of applied stress on shape memory characteristics of Ni50Ti45Cu5 (at.%) alloy subjected to thermomechanical cycling

“…Thermomechanical cycling tests were conducted using a custom-built thermomechanical cyclic testing machine, where the two ends of the wire specimen were crimped and attached to the holder, which in turn is fastened to the electrical connection (Figure 1). As the higher magnitude of stress decreases the fatigue life of an SMA component/device, 28,29 it can be improved by reducing the level of load applied. 19,30,31 However, reducing the stress level decreases the recovery strain.…”

Structural fatigue and fracture of shape memory alloy actuators: Current status and perspectives

“…The constant-stress loading condition refers to thermal variations under a constant bias load, which is an idealization of typical loading paths that utilize SMAs as actuators. In an effort to fill the gap between the test and working conditions, effects of the applied load level (Bigeon and Morin, 1996; Karakoc et al, 2018; Lagoudas et al, 2009), degree of transformation (complete vs partial; Bertacchini et al, 2003; Bhaumik et al, 2008; Lagoudas et al, 2009), loading constraints (constant stress vs constant strain; Scirè Mammano and Dragoni, 2014a), variable mechanical loading (linear stress-strain variation; Scirè Mammano and Dragoni, 2014a; Wheeler et al, 2013), upper cycle temperature (Karakoc et al, 2017, 2019), corrosion environment (Bertacchini et al, 2009; Schick, 2009), and intermittent overload cycles (Saikrishna et al, 2013b) were investigated. Higher fatigue lives were observed for lower applied load levels, lower degree of transformation per cycle, constant strain as opposed to constant stress, increased slope of linear stress-strain variation, lower upper cycle temperature, and for intermittent overload cycles, respectively.…”

Fatigue tests of superelastic NiTi wires: an analysis using factorial design in single cantilever bending

“…In addition, under specific conditions, SMA can Fatigue in SMA can be of two types: functional fatigue, which refers to the degradation of its functional properties (SME and SE, for example), and structural fatigue, associated with the microstructural damages in the material and the number of cycles the material resists before fracture occurs [15]. Over the years, both structural and functional fatigue of NiTi SMA have been studied from different perspectives and test conditions, mainly under cyclic tensile loading [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and also in bending-rotation tests [15,[31][32][33][34][35][36].…”