Papers by Keyword: Superelasticity

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Authors: Benoît Malard, Jan Pilch, Petr Šittner, Remi Delville, Caroline Curfs
Abstract: Recovery processes responsible for evolution of microstructures in 0.1mm thin cold-drawn Ni-Ti shape memory alloy wire heat treated by DC electric pulse were investigated by combination of in-situ tensile stress - strain, electrical resistance and X-ray diffraction measurements. The X-ray data were used to obtain direct experimental information on the evolution of the phase fractions, internal strain and defects in the microstructure evolving through activation of a sequence of recovery processes during the short time electropulse treatment. It is shown that superelastic functional properties of the treated Ni-Ti wire can be precisely set by controlling the progress of the recovery processes by prescribing the time evolution of temperature T(t) and tensile stress s(t) (displacement control) in the treated wire.
Authors: Wen Jie Ren, Jun Sen Jia, Xiang Shang Chen
Abstract: The shape memory alloys (SMAs) have received increasing interest attributed to their unique superelastic effect and the shape memory effect. The existing models of superelastic SMAs are generally complex for practical use. In this paper, cyclic loading tests of superelastic SMA wires are first performed. Based on the experiments, a simple constitutive model is set up. Simulations testify that the model can approximately describe the hysteretic characteristics of the superelastic SMA and the simulated mechanical parameters agree well with the experimental values.
Authors: Seung Hoon Nahm, Young Joo Kim, Jeong Min Kim, Dong Jin Yoon
Abstract: When the shape memory alloy(SMA) completely consists of austenite phase that shows the super-elastic property, if the external energies, such as stress, crack, propagation and lamination, etc. are increased in this alloy until the austenite phase was transformed into the martensite phase, they are enough to change the mean free path of electrons correlated with the electrical resistivity of materials in the microscopic point of view. On the basis of the above concept, we carried out the feasible study for SMA wire as a strain sensor using the super-elastic property of SMA. The SMA wires of diameter 41 ㎛ were utilized for a sensor material. The relationship between electrical resistivity and tensile properties of the Ni-Ti based SMA wires during tensile loading was investigated. Since the strain is very sensitive to the minute change of electrical resistance of SMA wire, it is possible to use the SMA wire as a sensor of such physical quantities. In the study, the possibility for the application of Ni-Ti SMA wire as a sensor was investigated. The sensing system was able to measure the strain up to 6 % with 0.22 % measuring error. The sensitivity described by the ratio of electrical resistivity showed 0.00005.
Authors: Hai Jun Zhou, Hong Hong Huang, Hua Zhang
Abstract: An experimental study on mechanical behavior of superelastic NiTi shape memory alloy (SMA) bar subjected to torsion was made. The SMA specimen was in round bar shape, material phase was austenite and stress mode was torsion. The test was carried out by applying repeated cyclic uniform torsional load. Strain rate, strain amplitude and number of cycles were considered as test parameters. The test was described and analyzed in terms of three fundamental mechanical quantities: secant stiffness, energy loss per unit weight and equivalent damping. The test results show that SMA bar subjected to torsion, have great potential for application in seismic devices due to their considerable superelasticity and stable cyclic behaviors.
Authors: T.W. Duerig, A.R. Pelton
Authors: Dinh van Hai, Hoang Minh Tam, Duong van Quang
Abstract: In this study, the effects of supereslasticity of Nitinol for self-expanding (SX) stents – Stent devices which are implanted into the blood vessels in order to restore blood flow in a diseased artery segment (narrowing of the blood vessel due to plaque build-up) and keep the artery open after angioplasty were considered and analyzed. To emphasize the unique properties of Nitinol as compared to other materials, this study was conducted to differentiate the behaviors of two types of stents which are made of Nititol and 316L stainless steel during implantation. Finite element analysis was used for simulation and modeling. The study results are expected to serve well the design of vessel stents.
Authors: Irina Khmelevskaya, Elena Ryklina, Andrey Korotitskiy
Abstract: The main fields of the practical application of Ti-Ni-based alloys, with shape memory and superelasticity effects, in engineering and medicine, have been identified in the past decade. There are temperature-sensitive elements for the actuators, damping devices, fasteners, medical instruments and implants (correctors, clamps, stents), for trauma, spine, dentistry, soft tissues and vessels. The development of science and high technologies to produce semi-finished methods (thin-walled tubes, tapes and thin wire), as well as processing methods (laser cutting and welding) of Ti-Ni-based shape memory alloys (SMA) over the last 10 years has contributed to the creation and implementation into practice of more complicated and advanced devices, based on solid and porous shape memory materials. New technologies require not only the creation of fundamentally new shape-memory devices, but also, more importantly, the achievement of the highest possible functional properties (FP) of the SMA, by creating an optimal type of structure by thermomechanical treatment. Techniques for the regulation of FP are different for Ti-Ni SMA of different compositions. For the non-ageing equiatomic and near-equiatomic Ti-Ni SMA, the basic method of FP control is thermomechanical treatment (ТМT), including severe plastic deformation (SPD), forming various structures: from a well-developed recovered and polygonized dislocation substructure to a nanocrystalline structure. In the framework of the scientific direction, fundamental and applied research in the field of SMA thermomechanical treatment (TMT) has been carried out since 1977, by the Shape Memory Alloys Research Group of the National University of Science and Technology MISIS.The present review provides a brief description of the devices running on the shape-memory effect and superelasticity, developed jointly by NUST "MISIS" and various companies: Globetek 2000 Ltd (Melbourne, Australia); Semashko Central Clinical Hospital of Ministry of Railway Communications; Closed Joint-Stock Company ARMGAS-NT; Scientific-production Enterprise AVTOMATPROM (Moscow, Russia), et al. In addition, it presents the analysis of medical problems that can be solved using data devices, including work items of thermomechanically treated Ti-Ni SMA.
Authors: Hiromasa Semba, Nagatoshi Okabe, Toru Yamaji, Keisuke Okita, Kiyoshi Yamauchi
Abstract: The bellows formed of TiNi shape memory alloy (SMA) is proposed as a new type of seismic protection device. The bellows structure is known to have lower rigidity along the axial direction through effect of its shape. TiNi is known to be one of the most typical SMAs, which have high damping characteristics for dynamics engaged in its twin formation under martensite state and have the ability to recover completely from the large strain after unloaded and or heated. In this study, fundamental compressive behavior of TiNi bellows was investigated and discussed. Several shapes of TiNi single-stage bellows produced by rubber bulge method were prepared. They were heat-treated for some heat treatments and then examined on compression tests. Based on the results, the relationships among the bellows shapes and the stiffness, energy-absorbing capacity and so on were clarified. Finally, it was found from these results that single-stage bellows of TiNi SMA could be used as one of seismic protection devices.
Authors: Franc Kosel, Borut Bundara
Authors: Surachai Dechkunakorn, Niwat Anuwongnukroh, Nuntinee Nanthavannich, Subongkoch Tongkoom
Abstract: Objectives: The aim of this study was to investigate and to compare the deactivation force, deactivation length and superelasticity in horizontal and vertical directions of Nickel-titanium (NiTi) orthodontic archwires made by 3 different manufactures. Materials and methods: The archwires tested were NiTi-OR (Ormco), NiTi-GH (G&H) and NiTi-H (Highland) and were 0.016 x 0.022 inch2 in cross-section and 25 mm in length. The study analysed load-deflection curves from three-point bending tests performed for each type of NiTi wire in vertical (occluso-gingival) direction (0.022” in horizontal dimension) and horizontal (bucco-lingual) direction (0.016” in vertical dimension) at oral temperature (37±10 oC). Statistical Analysis: Descriptive analysis and Kruskal Wallis test were performed to assess differences in deactivation force, deactivation length and superelasticity among the three brands. A p<0.05 was considered as significant. Results: The deactivation forces ranked from low to high were NiTi-GH, NiTi-OR and NiTi-H, 2.09, 2.57 and 2.90 N, respectively in horizontal dimension (occluso-gingival direction) and 3.04, 3.54 and 3.62 N in vertical dimension (bucco-lingual direction), respectively. For the deactivation length, ranking from long to short were NiTi-GH, NiTi-OR and NiTi-H, 1.08, 1.02 and 0.63 mm in horizontal dimension and 1.63, 1.46 and 1.13 mm in vertical dimension, respectively. In regards to superelasticity, NiTi-OR showed the highest superelasticity, 15.37 in horizontal and 9.68 in vertical dimension, followed by NiTi-GH, 9.51 for horizontal and 6.40 for vertical dimension and NiTi-H, 4.12 for horizontal dimension and 2.96 for vertical dimension. Conclusion: Deactivation force was higher in vertical than horizontal dimension and deactivation length was longer in vertical than horizontal dimension. However, the superelasticity was higher in horizontal than vertical dimension, except NiTi-H. The high priced NiTi wire (NiTi-OR) had the most superelasticity following by medium (NiTi-GH) and low priced wires (NiTi H).
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