Impact of Heat Effects on Superelasticity

Heller, Luděk; Šittner, Petr; Pilch, Ján

doi:10.1002/9781118803592.ch64

Cited by 5 publications

(9 citation statements)

References 10 publications

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“…Their results show that the dissipated energy decreases with increasing loading rate. Heller et al [6] studied the effect of heat transfer on pseudoelasticity of SMAs; their results show that the shape of the stabilized superelastic curve (transformation stress, strain, hysteresis area, slope in transformation range) depends significantly on the strain rate and that there exists a local maximum on strain rate dependence of the hysteresis area in the stabilized state at relatively slow strain rates. Constitutive models for SMAs have seen significant development in the last decades [7].…”

Section: Introductionmentioning

confidence: 99%

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

Zhang

Zhu

Moumni

et al. 2016

Smart Mater. Struct.

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This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

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Section: Introductionmentioning

confidence: 99%

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

Zhang

Zhu

Moumni

et al. 2016

Smart Mater. Struct.

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“…There are significant differences between the stress-strain curves measured in the liquid and in the air (higher forward transformation stress, wider hysteresis, and larger residual strain in the air). We ascribe these differences to the latent heat effects [11] at relatively high strain rate, which are supposed to be different in air and fluid and the wire hence deforms at different temperatures though nominally the temperature T = 37°C was held constant in both cases.…”

Section: Cyclic Tensile Deformation Of Superelastic Niti Wire In Biofmentioning

confidence: 99%

“…12d). The higher transformation stress at higher strain rates most likely originates from the impact of the latent heat effects on superelasticity [11] and fatigue performance might worsen with the increasing stress (Fig. 12d).…”

Section: The Effect Of Test Parameters On Fatigue Performancementioning

confidence: 99%

“…If the tests are performed at slow strain rates, they are painfully long. At higher strain rates in the air, however, the stress-strain responses are affected by the heat effects [11], particularly to the latent heat, thermomechanical coupling and heat exchange with the environment. If the fast cyclic loading tests are performed on NiTi wires immersed in fluids, this is not so serious due to much better heat exchange with the fluid, but there is a danger of environmental effects affecting the fatigue performance.…”

Section: Introductionmentioning

confidence: 99%

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Monitoring Tensile Fatigue of Superelastic NiTi Wire in Liquids by Electrochemical Potential

Racek

Stora²,

Šittner

et al. 2015

Shap. Mem. Superelasticity

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Fatigue of superelastic NiTi wires was investigated by cyclic tension in simulated biofluid. The state of the surface of the fatigued NiTi wire was monitored by following the evolution of the electrochemical open circuit potential (OCP) together with macroscopic stresses and strains. The ceramic TiO 2 oxide layer on the NiTi wire surface cannot withstand the large transformation strain and fractures in the first cycle. Based on the analysis of the results of in situ OCP experiments and SEM observation of cracks, it is claimed that the cycled wire surface develops mechanochemical reactions at the NiTi/liquid interface leading to cumulative generation of hydrogen, uptake of the hydrogen by the NiTi matrix, local loss of the matrix strength, crack transfer into the NiTi matrix, accelerated crack growth, and ultimately to the brittle fracture of the wire. Fatigue degradation is thus claimed to originate from the mechanochemical processes occurring at the excessively deforming surface not from the accumulation of defects due to energy dissipative bulk deformation processes. Ironically, combination of the two exciting properties of NiTi-superelasticity due to martensitic transformation and biocompatibility due to the protective TiO 2 surface oxide layer-leads to excessive fatigue damage during cyclic mechanical loading in biofluids.

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“…As such, the majority of studies carried out so far on NiTi thin films focused on the variation of the NiTi film’s mechanical and physical properties with the slowly varying temperature and stress [ 31 , 32 , 33 ]. When temperature and stress varies quickly (>10 Hz), additional problems with the periodically-generated/absorbed latent heat and dissipated heat accumulation appear [ 34 ]. The heat exchange between the nanocantilever and environment affects the potential use of NiTi thin films in tunable high-frequency nanoresonators, such as ultrasensitive physical and chemical sensors or RF filters.…”

Section: Introductionmentioning

confidence: 99%

Nanocantilevers with Adjustable Static Deflection and Significantly Tunable Spectrum Resonant Frequencies for Applications in Nanomechanical Mass Sensors

Stachiv

Šittner

2018

Nanomaterials

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Nanocantilevers have become key components of nanomechanical sensors that exploit changes in their resonant frequencies or static deflection in response to the environment. It is necessary that they can operate at a given, but adjustable, resonant frequency and/or static deflection ranges. Here we propose a new class of nanocantilevers with a significantly tunable spectrum of the resonant frequencies and changeable static deflection utilizing the unique properties of a phase-transforming NiTi film sputtered on the usual nanotechnology cantilever materials. The reversible frequency tuning and the adjustable static deflection are obtained by intentionally changing the Young’s modulus and the interlayer stress of the NiTi film during its phase transformation, while the usual cantilever elastic materials guarantee a high frequency actuation (up to tens of MHz). By incorporating the NiTi phase transformation characteristic into the classical continuum mechanics theory we present theoretical models that account for the nanocantilever frequency shift and variation in static deflection caused by a phase transformation of NiTi film. Due to the practical importance in nanomechanical sensors, we carry out a complete theoretical analysis and evaluate the impact of NiTi film on the cantilever Young’s modulus, static deflection, and the resonant frequencies. Moreover, the importance of proposed NiTi nanocantilever is illustrated on the nanomechanical based mass sensors. Our findings will be of value in the development of advanced nanotechnology sensors with intentionally-changeable physical and mechanical properties.

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Impact of Heat Effects on Superelasticity

Cited by 5 publications

References 10 publications

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

Energy-based fatigue model for shape memory alloys including thermomechanical coupling

Monitoring Tensile Fatigue of Superelastic NiTi Wire in Liquids by Electrochemical Potential

Nanocantilevers with Adjustable Static Deflection and Significantly Tunable Spectrum Resonant Frequencies for Applications in Nanomechanical Mass Sensors

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