Fatigue of Nitinol: The state-of-the-art and ongoing challenges

Mahtabi, Mohammad J.; Shamsaei, Nima; Mitchell, M. R.

doi:10.1016/j.jmbbm.2015.06.010

Cited by 169 publications

(100 citation statements)

References 110 publications

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“…Thus, for strain amplitudes where the material enters the stress-induced martensitic region, fully reversed strain-controlled tests are not fully reversed in stress-based fatigue analysis [1]. That being said, a mean stress/strain model for fatigue evaluation of the Nitinol should also be able to capture the effects of tension- For compressive strain amplitudes larger than 1.5%, the possibility of buckling was high, as a result maximum achievable strain level in fully reversed tests was limited to 1.5% to avoid buckling in the specimen.…”

Section: Cyclic Deformation Behaviormentioning

confidence: 99%

“…Therefore, understanding the fatigue behavior of Nitinol under nonzero mean strain loading condition is of great interest to many industries. Such an understanding can also facilitate further fatigue analyses under variable amplitude loads [1].…”

Section: Introductionmentioning

confidence: 96%

“…Popularity of Nitinol in various industries is resulted from its unique properties such as high energy dissipation, vibration absorption, good resistance to environmental attacks and nonmagnetic properties [1]. Following the successful performance of the shape memory alloys in the F-14 fighter jets, these alloys are frequently used in more aerospace applications.…”

Section: Introductionmentioning

confidence: 99%

“…Several studies [1,5,6] have investigated different aspects of property deterioration in Nitinol alloys. However, due to the complexities in mechanical behavior of this material, the fatigue behavior of Nitinol is not yet clearly understood.…”

Section: Introductionmentioning

confidence: 99%

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Mean Strain Effects on the Fatigue Behavior of Superelastic Nitinol Alloys: An Experimental Investigation

Mahtabi

Shamsaei

Rutherford

2015

Procedia Engineering

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Experimental fatigue study has been conducted in this paper to investigate the effects of mean strain on the fatigue behavior of superelastic Nitinol in short life regime. Nitinol alloys are used in many applications such as aerospace and bioengineering in which these alloys may be subjected to cyclic loading with mean strains/stresses. For traditional metals, presence of tensile mean strain/stress can significantly reduce fatigue lives. For superelastic Nitinol alloys, however, a more complex behavior is observed under tensile mean strains and ironically some beneficial effects of tensile mean strains have been reported in the literature. This paper aims to experimentally study the effects of tensile mean strains on the fatigue resistance of superelastic Nitinol alloys. Fatigue tests were conducted at room temperature (~24°C) where the material shows superelastic response. Strain-controlled uniaxial fatigue tests with and without tensile mean strains were conducted on standard solid circular specimens. Cyclic deformation and fatigue of the material was studied. Results from this study demonstrates the detrimental effects of mean strain on the fatigue of superelastic Nitinol at least for comparatively large strain amplitudes. Scanning electron microscopy (SEM) was used to investigate the fracture surface and observe the crack initiation sites. Inclusions such as TiC particles located at or near the surface were found to serve as the main crack initiation sites.

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Section: Cyclic Deformation Behaviormentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Mean Strain Effects on the Fatigue Behavior of Superelastic Nitinol Alloys: An Experimental Investigation

Mahtabi

Shamsaei

Rutherford

2015

Procedia Engineering

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“…However, the oxides formed on the nitinol surface always contain a certain fraction of Ni. [14][15][16][17][18][19] The main goal of this work was the performance of the series of experiments combined with vacuum-induction melting and continuous vertical casting of NiTi alloy in order to produce the strand. This was followed by the characterization of the obtained microstructure and finally we compared the electrochemical behaviour between a NiTi strand and commercially available nitinol.…”

Section: Introductionmentioning

confidence: 99%

Continuous vertical casting of a NiTi alloy

Stambolić¹,

Anžel²,

Lojen³

et al. 2016

Mater. Tehnol.

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In this paper we present research that is connected to the performance of a series of experiments combined with the vacuum-induction melting and continuous vertical casting of a NiTi alloy in order to produce the strand. The theoretical chosen parameters made it possible to obtain a continuously cast strand with a diameter of 11 mm. The strand microstructures were investigated with a light and scanning electron microscope, while the chemical composition of the single phase was identified with the semi-quantitative micro-analysis energy-dispersive X-ray spectroscopy and inductively coupled plasma -optical emission spectrometry. The research showed that the microstructure is dendritic, where in the inter-dendritic region the eutectic is composed of a dark NiTi phase and a bright TiNi3-x phase. In some areas we found Ti carbides and phases rich in Fe. The micro-chemical analysis of the NiTi strand showed that the composition changed over the cross and longitudinal sections, which is proof that the as-cast alloys are inhomogeneous. In the final part, the electrochemical behaviours of NiTi strand samples were compared to a commercially available NiTi cast alloy with the same composition. Keywords: NiTi alloy, continuous vertical casting, microstructure, potentiodynamic and impedance test V tem prispevku predstavljamo raziskavo, ki je povezana z izvedbo niza preizkusov vakuumskega pretaljevanja in so~asnega kontinuirnega vertikalnega litja NiTi zlitine s ciljem odliti palico. Teoreti~no izbrani parametri so omogo~ili, da smo uspeli kontinuirno odliti NiTi palico s premerom 11 mm. Dobljeno mikrostrukturo palice smo raziskali s svetlobnim in vrsti~nim elektronskim mikroskopom, kemijsko sestavo posameznih faz pa smo identificirali s semi-kvantitativno mikro-kemi~no analizo Energijsko disperzijsko spektrometrijo in z opti~nim emisijskim spektrometrom z induktivno sklopljeno plazmo. Preiskave so pokazale, da je mikrostruktura dendritska, medtem ko s v meddendritskem prostoru nahaja evtektik, sestavljen iz temne NiTi faze in svetle TiNi3-x faze. Mestoma smo identificirali tudi Ti karbide in fazo bogato s Fe. Mikro-kemi~na analiza NiTi palice je odkrila, da se sestava spreminja po prerezu in po dol`ini, kar nakazuje, da je zlitina po strjevanju nehomogena. V zaklju~nem delu smo primerjali elektrokemijsko obna{anje vzorcev NiTi palice s komercialno dostopno valjano NiTi zlitino enake sestave. Klju~ne besede: NiTi zlitina, vertikalno kontinuirno litje, mikrostruktura, potenciodinami~ni in impedan~ni test

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