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Shape Memory Waterborne Polyurethanes
Published in Ram K. Gupta, Ajay Kumar Mishra, Eco-Friendly Waterborne Polyurethanes, 2022
Arunima Reghunadhan, Jiji Abraham, Sabu Thomas
Shape memory materials show a special type of behavior, often termed pseudoelasticity, which is alternatively referred to as superelasticity. The superelasticity may be a consequence of a stress-induced alteration from austenite to martensite and back once a sample is tested between zero and a finite; however, tiny strain at a continuing close temperature on top of a set temperature is typically observed because of the austenite end temperature. The sample experiences very little or no permanent deformation in such a strain cycle, giving the impression that the fabric has undergone solely elastic deformation; consequently, the term super elastic is being used. The stresses suffered by superelastic materials in ordinary applications are minimal, but the rotations can be rather significant [7].
Shape Memory Materials
Published in D I Arun, P Chakravarthy, R Arockiakumar, B Santhosh, Shape Memory Materials, 2018
D I Arun, P Chakravarthy, R Arockiakumar, B Santhosh
Superelasticity or pseudoelasticity in SMAs is a phenomenon whereby the large strains induced by loading an SMA are recovered upon unloading. Superelasticity can be thought of as stress-driven shape memory in SMAs. By utilizing stress above the Ms temperature, the martensite in SMAs can be isothermally induced; this is known as stress-induced martensite (SIM). Upon the removal of stress, the shape memory vanishes and the original shape is memorized as an elastic material, which is mechanical shape memory rather than thermal shape memory. SMAs exhibit superelasticity because of two components: the formation of the reversible stress-induced martensite upon loading the alloy in its austenitic phase and its transformation back to the austenite phase upon unloading.
Biofunctionalization of NiTi Shape Memory Alloy Promoting Osseointegration by Chemical Treatment
Published in Sam Zhang, Hydroxyapatite Coatings for Biomedical Applications, 2013
Yanli Cai, Xianjin Yang, Zhenduo Cui, Minfang Chen, Kai Hu, Changyi Li
Nickel titanium (NiTi, also known as nitinol) is a metal alloy of nickel and titanium, in which the two elements are present in roughly equal atomic percentages. It undergoes a phase transformation in its crystal structure when cooled from the stronger, high-temperature form (austenite) to the weaker, low-temperature form (martensite). This thermoelastic martensitic phase transformation in the material is responsible for its extraordinary properties. These properties include shape memory effect and superelasticity (also called pseudoelasticity). Shape memory refers to the ability of NiTi to undergo deformation at one temperature and then recover its original, undeformed shape upon heating above its “transformation temperature.” The superelasticity occurs at a narrow temperature range just above its transformation temperature; in this case, no heating is necessary to cause the undeformed shape to recover, and the material exhibits enormous elasticity.
Dissimilar laser welding of NiTi to Ti6Al4V via Zr interlayer
Published in Materials and Manufacturing Processes, 2023
Fissha Biruke Teshome, Bei Peng, J. P. Oliveira, Zhi Zeng
Shape memory alloys (SMAs) are alloys known for unique functional properties of shape memory effect (SME) and superelasticity (SE). Solid state transformation between the martensite and austenite phases, which can be triggered by stress, temperature or presence of a magnetic field, are known to be responsible for these functional properties.[1] Owing to their SME and SE functional properties, NiTi alloys are demanded in multiple application areas including biomedical, aerospace and micro-electro-mechanical-systems (MEMS).[2–7] Ti6Al4V is the most used titanium alloy due to its favorable properties which include high strength-to-density ratio, corrosion resistance, and biocompatibility, making it desirable to the biomedical, automotive, and aerospace industries.[8,9]
Variable-parameter NiTi ultrasonic spot welding with Cu interlayer
Published in Materials and Manufacturing Processes, 2021
S. S. Ao, W. Zhang, C. J. Li, J. P. Oliveira, Z. Zeng, Z. Luo
NiTi shape memory alloys (SMAs) are known as smart engineering materials which exhibit excellent mechanical resistance, in addition to the shape memory effect and superelasticity.[1–3] These properties, combined with their biocompatibility, render NiTi to be highly appreciated in biomedical, aerospace, and civil engineering applications.[4–6] Nowadays, to further expand the potential applications of NiTi SMAs, it is necessary to develop joining methods with high efficiency and reliability owing to the difficulty in machining these materials. Different joining techniques such as laser[7–10] and electron beam welding[11] have been applied to obtain complex welding structures based on NiTi. However, traditional fusion welding methods give rise to the occurrence of potentially brittle intermetallic compounds and significantly influence the phase transformation behavior in the welded region.[1,7] These microstructural-induced changes result from the high-temperature thermal cycles during the welding process and have the tendency to limit the application conditions of these joints. To solve the above-mentioned problems, it is necessary to apply a processing method which can successfully achieve sound welding of NiTi, while persevering its functional and mechanical properties.
A study of pre-straining shape memory alloy (SMA)-based control elements subject to large-amplitude cyclic loads
Published in Ships and Offshore Structures, 2021
Shahin Zareie, Abolghassem Zabihollah
SMA is a kind of smart material, being able to return to the predefined shape after undergoing large deformation. This ability comes from two unique characteristics: shape memory effect (SME) and superelasticity (SE) (Mirzai et al. 2019; Aryan and Ghassemieh 2017; Mirzai et al. 2018; Zareie et al. 2019a). In the shape memory effect, the heat is needed to recover the shape, while in the superelasticity, the return to initial shape occurs upon removing the applied load (Salichs et al. 2001; Alipour et al. 2017; Mohd Jani et al. 2017). The SE state is a good alternative to use in the passive systems while the SME mode is a good solution to develop the semi-active system (Salichs et al. 2001; Alipour et al. 2017; Mohd Jani et al. 2017). Due to the simplicity of usage and no need for external heat, the SE-based system is proposed to utilise for structural control systems in offshore structures (Zareie et al. 2019b).