Shape memory and superelastic alloys

Yamauchi, Kiyoshi; Ohkata, I.; Tsuchiya, Kazuo; Miyazaki, S.

doi:10.1533/9780857092625

Cited by 153 publications

(74 citation statements)

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“…1) Couplings, fasteners, auto shut off valves, sensors and actuators are representative applications utilizing the shape memory effect. 2,3) Ti-Ni shape memory alloys also exhibit superelasticity, the unusual ability to undergo a large elastic deformation, 4,5) which makes them ideal to be used for cellular phone antennae, eyeglasses frames, orthodontic arch wires, guide wires and self-expanding stents. 2,3,6) Ti-Ni shape memory alloys have also been considered as attractive materials for biomedical implants.…”

Section: Introductionmentioning

confidence: 99%

Martensitic Transformation and Superelastic Properties of Ti-Nb Base Alloys

2015

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Ti-Nb base alloys have been proposed as prospective candidates for Ni-free biomedical superelastic alloys due to their excellent mechanical properties with good biocompatibility, and many kinds of Ti-Nb base alloys exhibiting shape memory effect or superelasticity have been developed up to now. However, typical Ti-Nb base superelastic alloys show a small recovery strain which is less than one third of the recovery strain of practical Ti-Ni superelastic alloys. Over the last decade there have been extensive efforts to improve the properties of Ti-Nb base superelastic alloys through microstructure control and alloying. Low temperature annealing and aging are very effective to increase the critical stress for slip due to fine subgrain structure and precipitation hardening. The addition of interstitial alloying elements such as O and N raises the critical stress for slip and improves superelastic properties. In this paper, the roles of alloying elements on the martensitic transformation temperature, crystal structure, microstructure and deformation behavior in the Ti-Nb base alloys are reviewed and the alloy design strategy for biomedical superelastic alloys is proposed.

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Section: Introductionmentioning

confidence: 99%

Martensitic Transformation and Superelastic Properties of Ti-Nb Base Alloys

2015

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“…One of the most frequently used smart material-based devices with flight heritage in actual space programs is SMAtype holding and release actuators [8][9][10]. Owing to their simplicity, reusability, high reliability against fatigue, and much lower shock levels than conventional pyrotechnic devices, these devices have been widely used in nonexplosive separation mechanisms for the release of mechanical constraints.…”

Section: International Journal Of Aerospace Engineeringmentioning

confidence: 99%

“…A large deformation of SMA can be reversed by changes in temperature or stress. Recently, SMA have found numerous applications in different fields of aerospace engineering, particularly in nonexplosive-type actuators for hold-and-release mechanisms [8][9][10].…”

Section: Design Description Of the Tilting Calibration Mechanismmentioning

confidence: 99%

Experimental Design Validation of Tilting Calibration Mechanism by Using Shape Memory Alloy Spring Actuator

Lee

Kim

2017

International Journal of Aerospace Engineering

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A tilting calibration mechanism is periodically deployed to view the reference temperature target during on-board calibration of a spaceborne imaging sensor and stowed after calibration. In the present work, we have proposed a new design strategy using a shape memory alloy (SMA) spring as an actuator that provides a fail-safe function to prevent the blocking of the main optical path when the mechanical driving part of the mechanism is stopped at a certain position during on-board calibration. Although a launch locking device was not considered in the design, this approach makes it possible to impose mechanical constraints on the driving part of the mechanism in severe launch vibration environments. The effectiveness of the proposed design was experimentally validated by a deploying and stowing function test and launch vibration environment tests such as a sine burst test, a random vibration test, and a pyroshock simulating impulse shock test. The test results demonstrated that the mechanism fulfills all the required functions for on-board calibration. The use of an SMA spring actuator was proved effective for implementing the dual function of a fail-safe in an emergency phase and a mechanical constraint on the driving part of the mechanism in severe launch vibration environment.

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“…Examples of applications include antennae and actuators in aerospace engineering, cardiovascular stents and dental braces in biomedical engineering, as well as eyeglass frames, fishing rods, and headbands of headphones in consumer products. A review of SMAs applications can be found in [127].…”

Section: Introductionmentioning

confidence: 99%

Computational modeling of size-dependent superelasticity of shape memory alloys

Qiao

Radovitzky

2016

Journal of the Mechanics and Physics of Solids

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The superelastic effect in shape memory alloys (SMAs) is attributed to the stressinduced reversible austenitic-martensitic phase transformations. It is characterized by the development of significant strains which are fully recoverable upon unloading, and also characterized by the stress-hysteresis in the loading and unloading cycle which corresponds to the energy dissipated during phase transformations. Recently, experiments have revealed size-dependent effects in the superelastic responses of SMAs at micro-and nanoscales. For instance, the CuAlNi microwires and submicron pillars show a substantially higher capacity for the energy dissipation than that of bulk samples, which offers a significant promise for the applications in protective materials.In this thesis, a continuum model is developed in order to improve our understanding of size effects in SMAs at small scales. The modeling approach combines classic superelastic models, which use the volume fraction as an internal variable to represent the martensitic phase transformation, with strain gradient plasticity theories. Size effects are incorporated through two internal length scales, an energetic length scale and a dissipative length scale, which correspond to the martensitic volume fraction gradient and its time rate of change, respectively. Introducing the gradient of the martensitic volume fraction leads to coupled macro-and microforce balance equations, where the displacements and the martensitic volume fraction are both independent fields. A variational formulation for the temporally-discretized coupled macro-and microforce balance equations is proposed, as well as a computational framework based on this formulation. A robust and scalable parallel algorithm is implemented within this computational framework, which enables the large-scale three-dimensional study of size effects in SMAs with unprecedented resolution. This modeling and computational framework furnishes, in effect, a versatile tool to analyze a broad range of problems involving size effects in superelasticity with the potential to guide microstructure design and optimization. In particular, the model captures the increase of the stress hysteresis and strain hardening in bulk polycrystalline SMAs for decreasing grain size, as well as the increase of the residual strain for decreasing pillar size in NiTi pillars. The model confirms that constraints like grain boundaries 3 and the surface Ti oxide layer are responsible for the size-dependent superelasticity in SMAs.

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Shape memory and superelastic alloys

Cited by 153 publications

References 0 publications

Martensitic Transformation and Superelastic Properties of Ti-Nb Base Alloys

Martensitic Transformation and Superelastic Properties of Ti-Nb Base Alloys

Experimental Design Validation of Tilting Calibration Mechanism by Using Shape Memory Alloy Spring Actuator

Computational modeling of size-dependent superelasticity of shape memory alloys

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