Modelling of SMA materials: Training and two way memory effects

An ideal model for stress-induced martensitic transformations in shape-memory alloys

“…The sequence of thermodynamic states occurring in SMAs is usually described by introducing additional variables (such as martensite and austenite volume fractions), within the framework of thermodynamics with internal state variables [8]. Current SMA constitutive models have reached a high level of sophistication accounting for multiple and simultaneous thermomechanical mechanisms [3][4][5][9][10][11][12][13]. Nevertheless, a common limitation is that most existing models generally assume that phase diagrams governing phase transformations are characterized by piecewise-linear transformation lines, despite of high non-linearities highlighted from experiments [6].…”

“…Proposed designs based on such materials range from aeronautic/mechanical applications (e.g., adaptive smart wings and actuators) and telecommunication devices (e.g., deployment and control mechanisms of satellites and antennas), to biomedical (e.g., self-expanding stents, orthodontic wires, and prostheses) and civil applications (e.g., devices for passive, active and semi-active controls of civil structures) [1,2]. As proved by the recent wide literature in the field [1,[3][4][5], there is a great need of constitutive models able to reproduce SMAs behavior, including a refined description of phase transformation mechanisms. In order to be effectively employed in practical applications, models should be characterized by parameters whose values have to be easily identified from well-established experimental procedures.…”

“…In this case, the behavior of the alloy in terms of the stress-strain relationship and alloy composition is analogous to the traction behavior. In fact, it can be obtained from previous relationships by replacing 2  with 3  Fig. 5a.…”

Experimental study of one‐dimensional superelastic capability of a nearly equi‐atomic NiTi shape memory alloy

“…Evolution of residual strains with cycle number chanical interpretations which are still under investigation. In particular, two micromechanical interpretations are discussed in literature [12] , one based on residual stresses due to the development of dislocation in the material during cycling, the other on residual permanent martensite accumulated during training. After a limited number of loading-unloading cycles, the stress-strain curves become steady gradually, and it is referred to as material training.…”

Cyclic behavior and energy approach to the fatigue of shape memory alloys

“…Residual strain is generally considered to be due to some oriented martensite not transforming back into austenite during reverse phase change [Lexcellent and Bourbon 1996;Auricchio et al 2003]. Repeated forward and reverse phase changes create some defects within the material [Abeyaratne and Kim 1997], which result in localized internal stresses [Tanaka et al 1995], allowing SMAs to exhibit twoway shape memory.…”