Experimental observations of “reversible” transformation toughening

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

“…This is the only required modification for calculating fracture toughness in terms of K. For measuring fracture toughness in SMAs in terms of the J -integral, a modification of ASTM standards regarding the determination of the elastic part of the J -value, J el , has been recently proposed in an effort to account for the mismatch among the apparent elastic properties of austenite, self-accommodated, and oriented martensite (Haghgouyan et al, 2019). In more recent papers (Makkar and Baxevanis, 2020;Makkar et al, 2021a), (i) the expected degree of improvement in the measurement accuracy by the aforementioned proposed modification to ASTM standards, the need for further modifications regarding, (ii) the uncertainty as to where to specify the fracture point on the obtained resistance curve, (iii) the specimen thickness requirement to ensure a constraint-independent measurement, and as well as (iv) the dependence of the measurements on the extent of unloading in the unloading/reloading cycles used to distinguish between the elastic and inelastic components in the incremental correction of J -value for advancing cracks have been discussed. It should be noted that according to the results presented in Haghgouyan et al (2019), the fracture toughness at temperatures below M d corresponds to martensite and that above M d to austenite; for nominal temperatures above M d the austenite phase is stable and the deformation response of the SMA is similar to that of a conventional ductile metal.…”

Fatigue Crack Growth in Austenitic and Martensitic NiTi: Modeling and Experiments

“…Both low-and high-cycle fatigue properties of NiTi SMAs were analyzed within the framework of modified approaches for common engineering metals [8][9][10][11][12][13][14][15]. Fracture-mechanics-based approaches were also used to analyze fatigue crack growth in SMAs [16][17][18][19]. Some of these works were motivated by special/critical needs for use in biomedical applications, such as the endovascular stents [20][21][22].…”