Failure analysis of NiTi wires used in medical applications

James, Brad; Foulds, J.R.; Eiselstein, Lawrence E.

doi:10.1361/154770205x70750

Cited by 16 publications

(14 citation statements)

References 5 publications

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“…Their results show that irreversible strain accumulates during testing in BRF experiments and that the surface cracks after increasing the cycling load stress which governs the fatigue life. Surface cracking was also observed by James et al [13] when pseudoelastic NiTi SMA wires were subjected to high strain levels on the compression side in bending and showed compressive damage failure mode occurs in these wires when the bending strain is higher than 20 %. Synchrotron radiation X-ray diffraction (SR-XRD) during in situ mechanical loading is a useful tool in understanding the phase behavior and therefore the mechanical response of pseudoelastic NiTi wires.…”

Section: Introductionsupporting

confidence: 57%

Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

Carl

Zhang

Young

2016

Shap. Mem. Superelasticity

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Shape memory alloys (SMAs) are a new generation of materials that exhibit unique nonlinear deformations due to a phase transformation which allows the material to return to its original shape after removal of stress or a change in temperature. These unique properties are the result of a martensitic/austenitic phase transformation through the application of temperature changes or applied stress. Many technological applications of austenitic SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this paper, commercial pseudoelastic NiTi SMA wires (50.7 at.% Ni) were placed under different bending strains and examined using scanning electron microscopy and high-energy synchrotron radiation X-ray diffraction (SR-XRD). By observing the microstructure, phase transformation temperatures, surface texture and diffraction patterns along the wire, it is shown that the wire exhibits a strong anisotropic behavior whether on the tensile or compressive side of the bending axis and that the initiation of micro-cracks in the wires is localized on the compression side, but that crack propagation will still happen if the wire is reloaded in the opposite direction. In addition, lattice strains are examined for both the austenite and martensite phases.

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Section: Introductionsupporting

confidence: 57%

Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

Carl

Zhang

Young

2016

Shap. Mem. Superelasticity

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“…The microvoids from the hydrogenembrittled samples appear to be much smaller than those observed in the nominal, as-received material [75].…”

Section: Resultsmentioning

confidence: 65%

“…Scanning electron microscopy (SEM) analyses showed a transition from a ductile-to-brittle fracture mode with increasing hydrogen content and a transition from a fracture surface showing evidence of microvoid coalescence morphology to one which exhibited a featureless, transgranular morphology [75,84]. The microvoids from the hydrogenembrittled samples appear to be much smaller than those observed in the nominal, as-received material [75].…”

Section: Resultsmentioning

confidence: 99%

“…Hydrogen (H) is known to have detrimental effects on the fracture properties of Ti alloys and NiTi is no exception [73,74]. Various investigations have shown that under certain conditions severe hydrogen embrittlement (HE) of NiTi SMAs can occur [39,56,59,73,[75][76][77][78][79][80][81][82][83]. Hydrogen can be absorbed into NiTi during pickling, plating, and caustic cleaning [74].…”

Section: B4 Stress Corrosion Cracking and Hydrogen Effects Of Nitimentioning

confidence: 99%

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Corrosion of Shape Memory and Superelastic Alloys

Eiselstein

2011

Uhlig's Corrosion Handbook

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“…However, in austenitic NiTi SMAs, full recovery of up to 5-10% strain is possible through an austenite-to-martensite phase transformation (Humbeeck, 1999;Otsuka and Ren, 2005;Elahinia et al, 2012;Dughaish, 2014). Since NiTi SMAs have such good mechanical properties, they are used for many applications, but one major concern is their fatigue life (Eggeler et al, 2004;Wagner et al, 2004;James et al, 2005;Figueiredo et al, 2009;Pelton et al, 2013). Eggeler et al (2004) examined the fatigue life of pseudoelastic NiTi SMA wires through low cycle loading and unloading during bending; they also looked at strain localization during the phase transformation.…”

Section: Introductionmentioning

confidence: 99%

High-energy synchrotron X-ray diffraction measurements of simple bending of pseudoelastic NiTi shape memory alloy wires

Zhang

Young

2016

Powder Diffr.

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Many technological applications of austenitic shape memory alloys (SMAs) involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity. In this paper, we investigated the effect of mechanical bending of pseudoelastic NiTi SMA wires using high-energy synchrotron radiation X-ray diffraction (SR-XRD). Differential scanning calorimetry was performed to identify the phase transformation temperatures. Scanning electron microscopy images show that micro-cracks in compressive regions of the wire propagate with increasing bend angle, while tensile regions tend not to exhibit crack propagation. SR-XRD patterns were analyzed to study the phase transformation and investigate micromechanical properties. By observing the various diffraction peaks such as the austenite (200) and the martensite (${\bar 1}12$), (${\bar 1}03$), (${\bar 1}11$), and (101) planes, intensities and residual strain values exhibit strong anisotropy, depending upon whether the sample is in compression or tension during bending.

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Failure analysis of NiTi wires used in medical applications

Cited by 16 publications

References 5 publications

Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

Texture and Strain Measurements from Bending of NiTi Shape Memory Alloy Wires

Corrosion of Shape Memory and Superelastic Alloys

High-energy synchrotron X-ray diffraction measurements of simple bending of pseudoelastic NiTi shape memory alloy wires

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