In various engineering fields such as civil, aerospace, and biomedical engineering, shape memory alloys (SMAs) have gained significant attention due to their unique characteristics. The nickel-titanium (NiTi) alloy is particularly prominent as the most widely utilized type of SMA, known for its high strength, superelasticity, corrosion resistance, excellent fatigue life, and notable damping capacity.
In practical scenarios like passive vibration control, SMAs frequently experience cyclic loading. Therefore, an in-depth analysis of the mechanical behavior of NiTi SMAs under such conditions is essential for ensuring their dependable use in engineering structures. A research team from the Department of Civil and Environmental Engineering at the University of Windsor in Canada has published a comprehensive study titled “Mechanical behavior of NiTi shape memory alloy under cyclic loading: A state-of-the-art review.”
This review primarily examines the macroscopic mechanical properties of NiTi SMAs when subjected to strain-controlled cyclic loading. It begins with a thorough overview of the phase transformation mechanisms in SMAs, which are responsible for the shape memory effect (SME) and superelasticity (SE). The review elaborates on the phase transitions between martensite and austenite, which are activated by changes in temperature or stress, and discusses how the composition and metallurgical processes affect transformation temperatures.
Furthermore, the mechanical properties of NiTi SMA are compared with those of other alloys such as Fe-Mn-Si SMA, Cu-Al-Ni SMA, and stainless steel. The document delves into the mechanical performance of NiTi SMA under cyclic loading, detailing aspects like the cyclic stress-strain relationship, thermal responses, and the impact of varying cyclic testing conditions.
The analysis identifies distinct features of the pseudoelastic stress-strain curves exhibited by NiTi SMA during cyclic loading, which include phenomena such as stress overshoot, undershoot, and stress drops. The thermal responses observed during these cycles, characterized by temperature fluctuations resulting from exothermic forward and endothermic reverse phase transformations, are also examined.
In addition, the review systematically summarizes the effects of key cyclic testing parameters—such as the number of cycles, strain amplitude, strain rate, temperature, pre-strain, specimen size, and loading mode—on mechanical responses including equivalent viscous damping, energy dissipation, stress plateaus, and residual strain.
The study also investigates the fatigue behavior of NiTi SMA, which encompasses both structural fatigue—leading to material failure due to the accumulation of microstructural damage—and functional fatigue, which results in the decline of mechanical properties like energy dissipation capacity and superelasticity. The concept of “training” to mitigate functional fatigue and stabilize material properties is introduced, along with insights into how training conditions influence the mechanical behavior of NiTi SMA.
Lastly, the review identifies existing gaps in research and suggests directions for future studies. These include exploring the combined effects of material composition and cyclic loading parameters, achieving a deeper understanding of heat balance and temperature evolution during cyclic loading, conducting research on larger SMA specimens, and developing scalable and cost-effective manufacturing techniques. The authors also emphasize the need to investigate the mechanical behavior of NiTi SMA under stress-controlled cyclic loading that corresponds to seismic frequencies, as well as to establish design guidelines for SMA-based structural components or devices.
The paper “Mechanical behavior of NiTi shape memory alloy under cyclic loading: A state-of-the-art review” is authored by Danial Davarnia, Shaohong Cheng, and Niel Van Engelen. The complete text of the paper is accessible at: https://doi.org/10.1007/s11709-025-1195-2.
