A statistical approach to understand the role of inclusions on the fatigue resistance of superelastic Nitinol wire and tubing

Robertson, Scott W.; Launey, Maximilien E.; Shelley, Oren; Ong, Ich; Vien, Lot; Senthilnathan, Karthike; Saffari, Payman; Schlegel, Scott; Pelton, Alan R.

doi:10.1016/j.jmbbm.2015.07.003

Cited by 52 publications

(77 citation statements)

References 15 publications

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“…They exhibit a high strength [6,7] and SM effects can be exploited many times before functional and structural fatigue limit service life [8][9][10][11]. NiTi SMAs also show good corrosion resistance and biocompatibility [12,13], such that they are attractive for medical applications.…”

Section: Introductionmentioning

confidence: 99%

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Birk

Biswas

Frenzel

et al. 2016

Shap. Mem. Superelasticity

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Pseudoelasticity (PE) in shape memory alloys relies on the formation of stress-induced martensite during loading and on the reverse transformation during unloading. PE yields reversible strains of up to 8 % and is applied in applications such as medical implants, flexible eye glass frames, damping elements, and others. Unfortunately, PE shows a strong temperature dependence and thus can only be exploited within a relatively narrow temperature window. The present work focuses on a related process, which we refer to as twinning-induced elasticity (TIE). It involves the growth and shrinkage of martensite variants which are stabilized by dislocations, which are introduced by appropriate cold work. TIE yields reversible strains of the order of 3 %. The TIE effect does not suffer from the strong temperature dependence of PE. The weak temperature dependence of mechanical TIE properties makes TIE attractive for applications where temperature fluctuations are large. In the present work, we study the TIE effect focusing on Ni 50 Ti 50 shape memory alloy wires. The degree of plastic pre-deformation of the initial material represents a key parameter of the ingot metallurgy processing route. It governs the exploitable recoverable strain, the apparent Young's modulus, and the widths of the mechanical hysteresis. Dynamic mechanical analysis is used to study the effects of pre-deformation on elementary microstructural processes which govern TIE.

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Section: Introductionmentioning

confidence: 99%

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Birk

Biswas

Frenzel

et al. 2016

Shap. Mem. Superelasticity

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show abstract

“…Robertson et al [1] tested diamond surrogates similar to those used in the current study made from three standard grade Nitinol materials and two high-purity grade materials specifically to examine the effects of material cleanliness on fatigue life. The compositions, transformation temperatures, and microstructural characteristics for the Standard Grade VAR, Standard Grade VIM-VAR, and Standard Grade VIM materials supplied by the mills are listed in Table 1 as Ingots A, B, and C, respectively.…”

Section: Tube Manufacturing Process Tm-2mentioning

confidence: 99%

“…With these considerations in mind, much attention has been paid to factors affecting the fatigue life of Nitinol to ensure long-term device efficacy. Initial fatigue studies [1,[6][7][8] using diamond samples meant to represent the fundamental construct of laser-cut devices and capture clinically relevant loading conditions, showed high-cycle fatigue strain limits on the order of 0.4-0.8%. As often occurs in wrought ductile structural alloys, non-metallic inclusions in the form of stringers resulting from axisymmetric working operations act as crack nucleation sites during high-cycle fatigue of Nitinol components.…”

Section: Introductionmentioning

confidence: 99%

“…As often occurs in wrought ductile structural alloys, non-metallic inclusions in the form of stringers resulting from axisymmetric working operations act as crack nucleation sites during high-cycle fatigue of Nitinol components. Recent efforts on the part of raw material producers to improve material cleanliness have resulted in notable increases in fatigue life [1,9]. Despite these efforts, however, there has been little published work exploring the effects of metal processing techniques on fatigue properties.…”

Section: Introductionmentioning

confidence: 99%

“…That was not done in the current effort as tube manufacturing processes at the related companies are considered intellectual property. However, as a result of the thorough and meticulous published work as delineated below [1], it is possible to compare the effects of TM-1 and TM-2 tube processing on fatigue life within the confines outlined herein. The resulting fatigue behaviors are correlated with statistical analyses of microstructures of these alloys and discussed in terms of traditional metallurgical tenets and novel computational modeling of the potency of primary inclusions in fatigue crack nucleation.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Tube Processing on the Fatigue Life of Nitinol

Adler

Frei²,

Kimiecik

et al. 2018

Shap. Mem. Superelasticity

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Nitinol tubes were manufactured from Standard Grade VIM-VAR ingots using Tube Manufacturing method ''TM-1.'' Diamond-shaped samples were laser cut, shape set, then fatigued at 37°C to 10 7 cycles. The 50, 5, and 1% probabilities of fracture were calculated as a function of number of cycles to fracture and compared with probabilities determined for fatigue data published by Robertson et al. (J Mech Behav Biomater 51:119-131, 2015). Robertson tested similar diamonds made from the same standard grade of Nitinol as in the current study, two other standard grades of Nitinol, and two high-purity grades of Nitinol expressly designed to improve fatigue life. Robertson's tubes were manufactured using Tube Manufacturing method ''TM-2.'' Fatigue performance of TM-1 and TM-2 diamonds were compared: At 10 7 cycles, strain amplitudes corresponding to the three probabilities of fracture of the TM-1 diamonds were 2-3 times those of the TM-2 diamonds made from the same grade of Nitinol, and comparable to TM-2 diamonds made from the higherpurity materials. This difference is likely a result of the differences in tube manufacturing techniques and effects on resulting microstructures. Microstructural analyses of samples revealed a correlation between the median probability of fracture and median inclusion diameter that follows an inverse power-law function of the form y & x -1 .

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NiTi‐Based Elastocaloric Cooling on the Macroscale: From Basic Concepts to Realization

et al. 2018

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Solid‐state cooling is an environmentally friendly, no global warming potential alternative to vapor compression‐based systems. Elastocaloric cooling based on NiTi shape memory alloys exhibits excellent cooling capabilities. Due to the high specific latent heats activated by mechanical loading/unloading, large temperature changes can be generated in the material. The small required work input enables a high coefficient of performance. An overview of elastocaloric cooling from basic principles, such as elastocaloric cooling cycles, material characterization, modeling, and optimization, to the design of elastocaloric cooling devices is presented. Current work performed within the DFG (Deutsche Forschungsgemeinschaft) Priority Program SPP 1599 “Ferroic Cooling”, which is focused on the development and realization of a continuously operating elastocaloric cooling device, is highlighted. The cooling device operates in a rotatory mode with wires under tensile loading. The design allows maximization of cooling power by suitable wire diameter scaling as well as efficiency optimization by implementing a novel drive concept. Finally, computer‐aided design (CAD) models of the discussed solid‐state air cooling device are presented.

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A statistical approach to understand the role of inclusions on the fatigue resistance of superelastic Nitinol wire and tubing

Cited by 52 publications

References 15 publications

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Effects of Tube Processing on the Fatigue Life of Nitinol

NiTi‐Based Elastocaloric Cooling on the Macroscale: From Basic Concepts to Realization

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