scholarly journals Phase transformation volume amplitude as a low-cycle fatigue indicator in nickel–titanium shape memory alloys

2020 ◽  
Vol 178 ◽  
pp. 442-446 ◽  
Author(s):  
Harshad M. Paranjape ◽  
Bill Ng ◽  
Ich Ong ◽  
Lot Vien ◽  
Christopher Huntley
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Low Cycle Fatigue ◽  
Nickel Titanium ◽  
Cycle Fatigue

Modeling of Internal Damage Evolution During Actuation Fatigue in Shape Memory Alloys

2018 ◽  
Author(s):  
Francis R. Phillips ◽  
Daniel Martin ◽  
Dimitris C. Lagoudas ◽  
Robert W. Wheeler
Keyword(s):  
Phase Transformation ◽  
Constitutive Model ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Damage Evolution ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Internal Damage ◽  
Functional Fatigue ◽  
Non Linear

Shape memory alloys (SMAs) are unique materials capable of undergoing a thermo-mechanically induced, reversible, crystallographic phase transformation. As SMAs are utilized across a variety of applications, it is necessary to understand the internal changes that occur throughout the lifetime of SMA components. One of the key limitations to the lifetime of a SMA component is the response of SMAs to fatigue. SMAs are subject to two kinds of fatigue, namely structural fatigue due to cyclic mechanical loading which is similar to high cycle fatigue, and functional fatigue due to cyclic phase transformation which typical is limited to the low cycle fatigue regime. In cases where functional fatigue is due to thermally induced phase transformation in contrast to being mechanically induced, this form of fatigue can be further defined as actuation fatigue. Utilizing X-ray computed microtomography, it is shown that during actuation fatigue, internal damage such as cracks or voids, evolves in a non-linear manner. A function is generated to capture this non-linear internal damage evolution and introduced into a SMA constitutive model. Finally, it is shown how the modified SMA constitutive model responds and the ability of the model to predict actuation fatigue lifetime is demonstrated.

scholarly journals Characterization Techniques of a Shape Memory Nickel Titanium Alloy

Proceedings ◽  
2020 ◽  
Vol 38 (1) ◽  
pp. 15
Author(s):  
Andrade ◽  
Soares ◽  
Nobrega ◽  
Hilário ◽  
Santos
Keyword(s):  
Differential Scanning Calorimetry ◽  
Titanium Alloy ◽  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Tensile Tests ◽  
Metallic Alloys ◽  
Nickel Titanium ◽  
Metallographic Analysis ◽  
Scanning Calorimetry

This paper presents a characterization processes study of metallic alloys, more specifically the shape memory alloys (SMA) composed by Nickel and Titanium (NiTinol). Two different wire suppliers were studied, starting with metallographic analysis until observe the contours of the grain wires. Differential scanning calorimetry (DSC) test was also performed to obtain phase transformation temperatures of the NiTinol alloys. Finally, after several tensile tests, some results were obtained for stresses, strains, elasticity modules and maximum rupture deformation.

High-Cycle Fatigue Criterion for Shape Memory Alloys Based on Shakedown Theory

2016 ◽  
Author(s):  
Wael Zaki ◽  
Xiaojun Gu ◽  
Ziad Moumni ◽  
Weihong Zhang
Keyword(s):  
Phase Transformation ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
High Cycle Fatigue ◽  
Cycle Fatigue ◽  
Mesoscopic Scale ◽  
Shakedown Theory ◽  
Elastoplastic Materials ◽  
Elastic Shakedown ◽  
Fatigue Criterion

Based on a recently developed shakedown theory for non-smooth nonlinear materials, we derive a criterion for high-cycle fatigue in shape memory alloys (SMAs). The fatigue criterion takes into account phase transformation as well as reorientation of martensite variants as the source of fatigue damage. The mathematical derivation of the criterion is based on the requirement of elastic shakedown for a given structure to achieve unlimited fatigue endurance. Elastic shakedown is defined as an asymptotic state in which damage due to time-varying load becomes confined at the mesoscopic scale, or the scale of the grain, with no discernable inelasticity at the macroscopic scale. From an energy standpoint, elastic shakedown corresponds to a situation where energy dissipation becomes bounded and the response elastic after a certain number of loading cycles. A sufficient condition to achieve this state was established by Melan (1936) [1] and Koiter (1960) [2] for elastoplastic materials and later generalized to hardening plasticity by Nguyen (2003) and to non-smooth non-linear materials by Peigney (2014). The latter formulation is applicable to SMAs obeying the ZM constitutive model (Zaki & Moumni, 2007) and is shown here to allow the derivation of a high-cycle fatigue criterion analogous to the one proposed by Dang Van (1973) for elastoplastic materials. The criterion allows establishing a safe domain in stress deviator space at the mesoscopic scale consisting of a hypercylinder with axis parallel to the direction of martensite orientation. The hypercylinder is delimited along its axis by two transverse hyperplanes representing bounds on admissible stress states consistent with the loading conditions for phase transformation. Safety with regard to high-cycle fatigue, upon elastic shakedown, is conditioned by the persistence of the macroscopic stress path, as the load varies and at every material point, strictly within the hypercylinder. The size of the hypercylinder is shown to strongly depend on the relative amount of martensite present in the SMA.

Multiscale TRIP-based investigation of low-cycle fatigue of polycrystalline NiTi shape memory alloys

2019 ◽  
Vol 115 ◽  
pp. 307-329 ◽  
Author(s):  
Yahui Zhang ◽  
Ziad Moumni ◽  
Yajun You ◽  
Weihong Zhang ◽  
Jihong Zhu ◽  
...  
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue ◽  
Niti Shape Memory Alloys

Low-Cycle Fatigue Behavior of Copper Zinc Aluminum Shape Memory Alloys

1999 ◽  
pp. 337-344 ◽  
Author(s):  
A. Subramaniam ◽  
N. Rajapakse ◽  
D. Polyzois ◽  
B. Yue
Keyword(s):  
Shape Memory Alloys ◽  
Shape Memory ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Cycle Fatigue ◽  
Copper Zinc
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