Fatigue Crack Growth Fundamentals in Shape Memory Alloys

Wu, Y.; Ojha, A.; Patriarca, L.; Şehitoğlu, Hüseyin

doi:10.1007/s40830-015-0005-4

Cited by 41 publications

(25 citation statements)

References 38 publications

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“…As noted in our previous work [54], the martensite moduli are higher than austenite moduli. The higher martensite modulus creates favorable fatigue crack growth resistance as noted in early work [49].…”

Section: Discussion Of Resultsmentioning

confidence: 75%

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Superelasticity and Shape Memory Behavior of NiTiHf Alloys

Şehitoğlu

Patriarca

et al. 2017

Shap. Mem. Superelasticity

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The NiTiHf high-temperature shape memory alloys represent a significant advancement in extending the functionality of binary NiTi to elevated temperatures above 100°C. Despite this potential, the previous results in the literature point to a disappointingly low shape memory strains with addition of Hf. On the other hand, based on theoretical analysis using the lattice constants, the transformation strains should increase substantially with increase in Hf content. The present paper addresses this discrepancy, and using atomistic simulations, determination of twinning modes in martensite with transmission electron microscopy, digital image measurements of habit plane orientation, and strains in single-crystal specimens show that the experimental transformation strains in NiTiHf indeed increase with increasing Hf to unprecedented strain levels near 20%. The Hf contents considered were in the range 6.25-25 at.%, and NiTi (0% Hf) results are provided as the baseline. The current work represents more than 60 experiments representing an extremely thorough study on single crystals and polycrystals.

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Section: Discussion Of Resultsmentioning

confidence: 75%

“…The experimental points are obtained using local strain measurements via digital image correlation (DIC). The details of DIC method can be found in [25,48,49]. Local strains determined with DIC technique establish the maximum transformation strains for the specific crystal orientation.…”

Section: Comparison Of Experimental Results and Theoretical Resultsmentioning

confidence: 99%

Superelasticity and Shape Memory Behavior of NiTiHf Alloys

Şehitoğlu

Patriarca

et al. 2017

Shap. Mem. Superelasticity

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“…The other question has to do with the reasons behind the large transformation strains in NiTiHf alloys [81]. The lattice constants for austenite and martensite and the monoclinic angle of the martensite dictate the stretch tensors.…”

Section: Discussion Of Resultsmentioning

confidence: 99%

Shape memory strains and temperatures in the extreme

Şehitoğlu

Patriarca

2017

Current Opinion in Solid State and Materials Science

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It is well known that the achievement of high transformation strains in shape memory alloys (SMAs) has been curtailed by plastic deformation mediated via dislocation slip. In particular, the utilization of SMAs at high temperatures is also hindered by plastic slip. In this paper, an overview of the most important SMAs is provided by constructing transformation strain, transformation temperature, and slip resistance plots to put existing works in perspective. To this plots, we added results on NiTiHf alloys which impart both high temperature capability and high slip resistance at unprecedented levels. The remarkable finding is that NiTiHf alloys can undergo transformation strains near 20% and transformation temperatures exceeding 400 °C

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“…Recently, experimental investigations adopting local DIC measurements were performed on a Ni-based single crystal alloy [21][22][23], and also on shape memory single crystals [24]. These studies highlight the importance of DIC measurements to quantify the effect of the microstructure (i.e.…”

Section: Figmentioning

confidence: 99%

LCF and crack growth: recent results obtained by DIC

2018

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Abstract. Nowadays, several components for aerospace and energy applications (i.e., turbine disks, offshore pipelines, and combustor chambers) are designed following a safe-life approach in the low cycle fatigue (LCF) regime. As also in the LCF regime it is worth adopting a damage tolerance design, fatigue life is assessed considering a crack propagating from the first load cycle, starting from an initial defect present in the component's most-stressed region or from a microstructural feature. In this frame, fatigue crack growth is described considering LCF conditions, where the driving force at the crack tip can be described with the ΔJ eff parameter. The paper aims to give an overview of the potential applications and perspectives for the adoption of digital image correlation (DIC) measurements to study LCF nucleation and propagation. A visual technique based on the DIC displacement fields was developed to measure crack opening and closing levels in the presence of large strains. The technique is applied to different materials (steels, AlSi10Mg, nickel-based super-alloys). In addition, further applications of the DIC strain measurements are revised for the study of the nucleation stage and the crack tip process zone.

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Fatigue Crack Growth Fundamentals in Shape Memory Alloys

Cited by 41 publications

References 38 publications

Superelasticity and Shape Memory Behavior of NiTiHf Alloys

Superelasticity and Shape Memory Behavior of NiTiHf Alloys

Shape memory strains and temperatures in the extreme

LCF and crack growth: recent results obtained by DIC

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