On stability of NiTi wire during thermo-mechanical cycling

Saikrishna, C.N.; Ramaiah, K.V.; Prabhu, Sankaralingam; Bhaumik, SK

doi:10.1007/s12034-009-0049-1

Cited by 29 publications

(10 citation statements)

References 17 publications

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“…The stability of the microstructure ensured that progression of dislocations, and crack growth was slowed in the trained T-LP material, leading to the longer fatigue life than the LP material [12,29]. The nanocrystalline material impeded the dislocation activity of transformation induced plasticity, delaying crack initiation in these materials [45][46][47]. The majority of high cycle fatigue life in NiTi is in the crack initiation stage, with propagation occurring rapidly once the critical crack size is reached [48], which accounts for the uniformity of the fracture surfaces in Figure 11b and c. Brittle inclusions located at the surface serve as the crack initiation points [49].…”

Section: Thermal and Physical Propertiesmentioning

confidence: 99%

Effects of post-processing on the thermomechanical fatigue properties of laser modified NiTi

Panton

Michael

Zhou

et al. 2019

International Journal of Fatigue

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The multifunctional capabilities needed for advanced shape memory alloys (SMA) actuators has been shown to be achievable by locally tuning the properties through laser processing. Before the wide-spread use of these SMAs is realized, a detailed understanding on the long-term stability and functional life span of these material must be achieved. The current study systematically investigates the effects of thermomechanical treatment on laser modified NiTi wires, while comparing them to the original base material. Surface analysis was done using a scanning electron microscope (SEM), while microstructure analysis was performed using transmission electron microscopy (TEM). Mechanical properties were assessed using standard tensile tests and a custom built thermomechanical fatigue. Results showed that the coarse-grains, large precipitates and surface defects associated with as laser modified NiTi resulted in reduced mechanical performance. However, subsequent thermomechanical treatment restored the refined microstructure and mechanical performance similar to the base material while providing the added functionality.

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Section: Thermal and Physical Propertiesmentioning

confidence: 99%

Effects of post-processing on the thermomechanical fatigue properties of laser modified NiTi

Panton

Michael

Zhou

et al. 2019

International Journal of Fatigue

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“…6a). With classical heat treatments, strain hardening are classically observed in cold worked material directly aged as in Saikrishna et al (2009) or annealed and aged as in Jiang et al (2009). Materials having linear and potentially elastic behaviour after transformation plateau, with important tensile strength, have already been observed in Pilch et al (2009) with Joule heating but have never been obtained with conventional heat treatments to the knowledge of authors.…”

Section: Brittle Behaviour Vs Strain Hardeningmentioning

confidence: 99%

Study of electropulse heat treatment of cold worked NiTi wire: From uniform to localised tensile behaviour

Delobelle

Chagnon

Favier

et al. 2016

Journal of Materials Processing Technology

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International audienceElectropulse heat treatment is a technique developed to realise fast heat treatment of NiTi shape memory alloys. This study investigates mechanical behaviour of cold worked NiTi wires heat treated with such a technique. It is demonstrated that milliseconds electropulses allow to realise homogeneous heat treatments and to adapt the mechanical behaviour of NiTi wires by controlling the electric energy. The material can be made elastic with different elastic modulus, perfectly superelastic with different stress plateau levels and superelastic with important local residual strain. Due to the short duration and high temperature of the heat treatment, this technique allows to obtain mechanical properties that cannot be obtained with classical heat treatments of several minutes in conventional furnaces such as linear evolution of the final loading and high tensile strength to 1500 MPa for superelastic material or increase of the stress plateau level with cycling for superelastic material

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“…This annealing condition ensures a large grain size -the amorphous bands start to crystallize without completely annealing the structural defects in the material, as crystallite nucleation is supressed [18]. This step is essential for the material to recover from any previous cold work or damage it has sustained and to stabilize transformation characteristics [18].…”

Section: Specimen Preparationmentioning

confidence: 99%

“…Fatigue Ð Previous studies have reported on a continuous change in the functional properties of the NiTi such as the transformation temperatures, transformation hysteresis and strain response under thermo-mechanical cycling [18]. Our experimental work comprises 132 tests, which effectively subject the 3 test specimens to thermo-mechanical cycling throughout the study; hence, the stability of the material response is a concern.…”

Section: Predictions and Limitationsmentioning

confidence: 99%

In situ Observation of NiTi Transformation Behaviour: A Micro–Macro Approach

Wickramasinghe

Tomlinson

Rongong

2014

Experimental and Applied Mechanics, Volume 6

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ABSTRACT:A novel experimental investigation is presented of thermally and stress induced transformation behaviour of a Polycrystalline NiTi Shape Memory Alloy (SMA) plate for flexural-type applications: In situ techniques are employed to allow simultaneous macroscopic and microstructural observation of the SMA in a 4-point flexural test. Forming part of a wider research towards realising a NiTi SMA Variable Stator Vane assembly for the gas turbine engine, the study explores variables critical to flexural-type morphing NiTi structures: (1) temperature; (2) strain; and (3) cyclic loading. It builds a relationship between the macro and micro response of the SMA under these key variables and lends critical implications for the future understanding and modelling of shape memory alloy behaviour for all morphing applications. This paper presents the methodological aspects of this study. KEYWORDS:Shape memory; NiTi; In situ; Phase transformations; Micro-macro approach; Cyclic loading INTRODUCTIONGas turbine performance development has been governed traditionally by the Òworst caseÓ deterioration and operating condition [1]. This leads to severe compromises and large safety margins. Active control of the engine operation using smart materials could potentially improve engine efficiency. Shape Memory Alloys (SMAs), a class of smart materials, exhibit several desirable characteristics exploitable for this purpose. NiTi, based on an equiatomic compound of nickel and titanium is the most widely used SMA in commercial applications [2]. Besides the ability of tolerating relatively large amounts of shape memory strain, NiTi shows high stability in cyclic applications, possesses an elevated electrical resistivity, and is corrosion resistant [3].

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On stability of NiTi wire during thermo-mechanical cycling

Cited by 29 publications

References 17 publications

Effects of post-processing on the thermomechanical fatigue properties of laser modified NiTi

Effects of post-processing on the thermomechanical fatigue properties of laser modified NiTi

Study of electropulse heat treatment of cold worked NiTi wire: From uniform to localised tensile behaviour

In situ Observation of NiTi Transformation Behaviour: A Micro–Macro Approach

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