Abstract
Amongst various intermetallic shape memory alloys (SMAs), nickel–titanium-based SMAs (NiTi) are known for their unique elastocaloric property. This widely used shape remembering material demonstrates excellent mechanical and electrical properties with superior corrosion resistance and super-long fatigue life. The straight-drawn wire form of NiTi has a maximum restorable strain limit of ~4%. However, a maximum linear strain of ~20% can be attained in its coil spring structure. Various material/mechanical engineers have widely exploited this superior mechanic characteristic and stress-triggered heating/cooling efficiency of NiTi to design smart engineering structures, especially in actuator technologies. This short technical note reflects the characteristics of the NiTi coil spring structure with its phase transformations and thermal transformation properties. The micro-actuators based on NiTi have been found to be possible, suggesting uses from biomedical to advanced high-tech applications. In recent years, the technical advancements in modular robotic systems involving NiTi-based SMAs have gained speculative commercial interest.
Highlights
Tetsuro Mori, an eminent senior engineer of Yaskawa Electric Corporation, in 1969, coined the word “mechatronics”
Shape memory alloys (SMAs) are broadly used in the development of thermostatic and electromechanical actuators, to perform mechanical actions assisted by temperature change phenomena via electric currents
This short technical note is a concise summary of the understanding of the properties of nickel–titanium-based SMAs (NiTi) coil springs
Summary
Tetsuro Mori, an eminent senior engineer of Yaskawa Electric Corporation, in 1969, coined the word “mechatronics”. Since SMAs are unidirectional actuators, external stress must be applied to strain it to its detwinned state, and to relapse its highly organized (austenite) crystal structure, thermal acceleration is essential [19]. The thermal shape memory effect of SMAs during the actuation cycle involves two stable phases, namely austenite and martensite. Since SMAs are unidirectional actuators, external stress must be applied to strain it to its detwinned state, and to relapse its highly organized crystal. Depending onthe thecustomized customized applications, NiTi is external stress must be applied to strain it to its on detwinned state, andapplications, to relapse itsNiTi highly fatigue behavior and sturdiness. B2 structure teredencountered in the austenitic phase, resembling cesium chloride (cubic crystal(cubic lattice structure), in was in the phase, resembling crystal
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