Nonuniform transformation behaviour of NiTi in a discrete geometrical gradient design

Shariat, Bashir S.; Bakhtiari, Sam; Liu, Yinong

doi:10.1016/j.jallcom.2018.09.116

Cited by 18 publications

(12 citation statements)

References 47 publications

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“…In NiTi, the material gradient can be acquired in microstructure by variation in heat treatment [7][8][9] or in composition by variation in Ni/Ti ratio [10][11][12]. In addition, by variation in the geometry of NiTi structure, the alloy experiences a nonuniform stress field upon loading, thus progressive martensitic transformation within the structure is achieved [13][14][15].…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

“…experimentation [13,17]. In the present study, thermal fields of superelastic NiTi structures with uniform and nonuniform geometries during stress-induced transformation are obtained by a high-resolution infrared camera and the martensitic transformation propagation is investigated for different types of geometries.…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

“…It has been reported that the magnitude of stress window is mainly dependent on the aspect ratio of the geometrically graded structure. As the aspect ratio decreases, the magnitude of stress window increases, which results in better controllability of the shape memory component [5,13].…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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Computational and experimental analyses of martensitic transformation propagation in shape memory alloys

Shariat

Bakhtiari

Yang

et al. 2019

Journal of Alloys and Compounds

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This study investigates the creation of heterogeneous martensitic transformation field in shape memory alloy structures with geometrical nonuniformity through experiments and finite element computational analysis.Geometrically graded superelastic NiTi thin plates with series and parallel design configurations with respect to the loading direction have been created. The nonuniform transformation evolutions within these structures are presented by thermal images captured by an infrared camera during tensile experimentation. It is found that the transformation propagation is along the loading direction in a sample with the series design configuration unlike that in a sample with the parallel design configuration. Also, the geometrically graded structures exhibit stress gradient over stress-induced transformation. The transformation propagation and the deformation behaviour of these structures are presented by numerical modelling which is in good agreement with experimental data.

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Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%

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Computational and experimental analyses of martensitic transformation propagation in shape memory alloys

Shariat

Bakhtiari

Yang

et al. 2019

Journal of Alloys and Compounds

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“…These properties originate from the thermoelastic martensitic transformations in these alloys [2,3]. Owing to these remarkable properties, they have been used in many innovative designs, both in end product applications, such as low power actuators in automotive industry [4], wing morphing control in aerospace engineering [5], miniature actuators in microelectromechanical systems (MEMS) [6], actuators in robotics [7] and biomedical devices [8], and in novel materials designs, such as intermetallic composites [9], functionally graded designs [10][11][12][13], and smart architectured materials [14]. To meet demands of different applications, their martensitic transformation characteristics and thermomechanical properties often need to be altered and controlled.…”

Section: Introductionmentioning

confidence: 99%

Monoclinic angle, shear response, and minimum energy pathways of NiTiCu martensite phases from ab initio calculations

Bakhtiari

Liu

et al. 2019

Acta Materialia

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Ti50Ni50-xCux alloys are observed to exhibit multiple martensitic transformations from B2 to an orthorhombic B19 and a monoclinic B19′ phase. In addition, DFT calculations have predicted a B19ʺ phase with a higher monoclinic angle as the thermodynamically stable ground state. This study investigated the effects of Cu content and shear stress on the monoclinic angles, phase stabilities of the various martensites, the minimum energy pathways, and the relative total energies among the phases in this pseudo-equiatomic Ti(Ni50-xCux) system. A new monoclinic phase (B19M) with a monoclinic angle lower than that of B19′ was found at above a critical Cu content. This confirms the formation of an intermediate phase in the martensitic transformation sequence of the pseudo-equiatomic Ti(Ni50-xCux) system but contradicts the crystal structure of the experimentally observed phase. It was found that the monoclinic angles of both B19M and B19ʺ decrease with increasing the magnitude of an opposing shear stress to their monoclinic distortion. At above certain critical values of the opposing shear stress, the B19M and B19ʺ phases destabilise and transform to lower monoclinic angle phases. In addition, the evidence suggests that the experimentally observed monoclinic B19′ phase is in fact a distorted B19ʺ with a reduced monoclinic angle under an opposing shear stress. With the same argument, the experimentally reported B19 phase is a metastable phase formed under the effect of an opposing shear stress to the monoclinic distortion of B19M.

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“…shows the comparison of the response of geometrically graded structures with parallel and series design configurations[23,25].Fig. 8(a) shows the comparison of the global deformation behaviour of three Ti-50.8at%Ni samples: a uniform strip (black curve), a twostrip structure with parallel design configuration (red curve), and a geometrically graded plate with series design configuration as per design concept of Fig.…”

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confidence: 99%

Modelling and experimental investigation of geometrically graded shape memory alloys with parallel design configuration

Shariat

Liu

Bakhtiari

2019

Journal of Alloys and Compounds

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Nonuniform transformation behaviour of NiTi in a discrete geometrical gradient design

Cited by 18 publications

References 47 publications

Computational and experimental analyses of martensitic transformation propagation in shape memory alloys

Computational and experimental analyses of martensitic transformation propagation in shape memory alloys

Monoclinic angle, shear response, and minimum energy pathways of NiTiCu martensite phases from ab initio calculations

Modelling and experimental investigation of geometrically graded shape memory alloys with parallel design configuration

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