Papers by Keyword: Shape Memory Alloy (SMA)

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Authors: Francisco Manuel Braz Fernandes, Karimbi Koosappa Mahesh, Corneliu Marius Crăciunescu, João Pedro Oliveira, Norbert Schell, Rosa Maria Miranda, Luisa Quintino, José Luis Ocaña
Abstract: The demand of emerging joining techniques for shape memory alloys (SMA) has become of great importance, as their functional properties, namely shape memory effect (SME) and superelasticity (SE) present unique solutions for state-of-the-art applications. Literature shows that significant efforts have been conducted on laser welding of these alloys, although very limited results concerning mechanical properties are repeatedly achieved. A better understanding of the mechanical behaviour of these welded joints may be got through a detailed analysis of the structural characteristics of the material from the base metal to the weld bead. Such studies have been carried out on a series of Ni-rich Ni-Ti SMA laser welded plates using synchrotron radiation.
Authors: Hong Tao Liu, Guang Ai Sun, Yan Dong Wang, Bo Chen, Xiao Lin Wang, Qiang Tian
Abstract: The stress-induced martensitic transformation in Ni47Ti44Nb9 was examined using X-ray diffraction (XRD) during in situ uniaxial loading and unloading. A new martensitic (020) peak in XRD patterns is observed under strain from 10% to 12%. It indicates that the martensitic texture has reached the optimum orientation. After unloading, approximately 8% irreversible strain still remains. It is associated with the reorientation of martensites and the plastic deformation of the B2-phase. In addition, the deformed β-Nb particles would also reduce the driving force for the reverse transformation. The details of lattice-strain and shared applied stress (SAS) in the B2-phase and β-Nb phase are also discussed in this work.
Authors: Sergey Dubinskiy, Vladimir Brailovski, Sergey Prokoshkin, Karine Inaekyan
Abstract: The technique and preliminary results of in situ X-ray diffraction analysis of the martensitic transformation in the newly developed Ti-Nb-Zr SMA for biomedical application are presented. To perform the in situ analysis, an original tensile stage, powered by a Ti-Ni SMA actuator and fit within the “TTK450” thermal chamber of a “PANalytical X’Pert Pro” diffractometer is designed, manufactured and validated. The tensile stage working principle and analysis methodology are described in detail. Preliminary results obtained during in-situ X-ray analysis of the phase transformations in Ti-Nb-Zr SMA are also presented.
Authors: Arne Biesiekierski, James Wang, Cui'e Wen
Abstract: In the realm of bioimplantation, titanium-based Shape Memory Alloys (SMAs) exhibit phenomenal versatility, with successful application in diverse fields. One area of particular interest is that of orthopaedics, where the unique properties of SMAs offer a range of benefits. That said, existing alloys still have unresolved issues concerning biocompatibility and osseointegration. Primary concerns include carcinogenicity, allergenicity and a significant mismatch between the Young’s moduli of bone and osteoimplants; issues that could be addressed via a novel porous titanium alloy. With that in mind, this paper seeks to provide a review identifying promising candidates for new, perfectly biocompatible alloys for production via powder metallurgy. Furthermore, an attempt will also be made to summarise existing research into appropriate methods for the production of a porous Ti-based SMA implant.
Authors: Sergey Prokoshkin, Vladimir Brailovski, Karine Inaekyan, Andrey Korotitskiy, Sergey Dubinskiy, Mikhail R. Filonov, Mikhail Petrzhik
Abstract: The processes of structure formation in Ti-Ni and in Ti-Nb-Zr, Ti-Nb-Ta shape memory alloys (SMA) under thermomechanical treatment (TMT) were studied. The TMT comprised cold rolling with true strains from e=0.25 to 2 and post-deformation annealing. Differences in these processes between two groups of alloys are considered. The main conclusions are as follows: nanostructures created by TMT are useful for radical improvement of the SMA functional properties, and an optimum nanostructure (nanocrystalline structure, nanosubgrained structure or theirmixture) should be selected by taking into account other structural and technological factors.
Authors: Xiang He Peng, Min Mei Chen, Jun Wang
Abstract: A constitutive model is developed for shape memory alloys (SMAs) based on the concept that an SMA is a mixture composed of austenite and martensite. The deformation of the martensite is separated into elastic, thermal, reorientation and plastic parts, and that of the austenite is separated into elastic, thermal and plastic parts. The volume fraction of each phase is determined with the modified Tanaka’s transformation rule. The typical constitutive behavior of some SMAs, including pseudoelasticity, shape memory effect, plastic deformation as well as its effects, is analyzed.
Authors: Ioan Doroftei, Florentina Adăscălitei
Abstract: The conventional mechanisms with stiff joints make the robots more complex, heavy, large and expensive. As walking robots are requested to perform tasks in rough terrain, the development of actuators capable to flexibly adapt to the unstructured environment becomes more and more necessary. Biological mechanisms like legs with high effectiveness and developing high forces are very common in nature. This is why introducing such structures in robotics is one of the most popular research in biomimetics. A wide variety of artificial muscles as actuators in robotics have been investigated till now. Shape Memory Alloys are a category of such artificial muscles which can be used as actuators in the structure of a biomimetic walking robot. In this paper, mechanisms that can convert the small strain of a SMA wire into large motion, used as legs for a hexapod walking micro-robot, are discussed.
Authors: Wei Wang, Ji Yuan Liu
Abstract: A multidimensional constitutive model for shape memory alloys (SMA) is developed in the paper, which is based on the thermodynamics theories of free energy and dissipation energy. This model can well describe both the shape memory effect (SME) and super elasticity effect (SE) of the thin-walled SMA cylinder under an axial tensional force and torsion.
Authors: Shuang Wu, Shou Gen Zhao, Da Fang Wu, Xue Mei Yu
Abstract: The methods of constitutive modeling of restrained recovery for Shape memory alloys (SMAs) were described in this paper and experiments were carried out to provide the essential data for the methods. The present mathematical constitutive models are inconvenient for engineering applications. Then a back propagation (BP) neural network model was developed for restrained recovery of SMAs. This BP neural network model can learn the hysteresis of SMAs in the process of heating and cooling based on its properties of nonlinear function mapping and adaptation, and it can predict the complete restrained recovery stress of SMAs with different initial strains. The predicted results obtained from the proposed BP model agree well with the experimental data. Moreover, the proposed BP model is more simple, convenient and low cost compared with the present mathematical constitutive models.
Authors: Wen Jie Ren, Jun Sen Jia, Xiang Shang Chen
Abstract: The shape memory alloys (SMAs) have received increasing interest attributed to their unique superelastic effect and the shape memory effect. The existing models of superelastic SMAs are generally complex for practical use. In this paper, cyclic loading tests of superelastic SMA wires are first performed. Based on the experiments, a simple constitutive model is set up. Simulations testify that the model can approximately describe the hysteretic characteristics of the superelastic SMA and the simulated mechanical parameters agree well with the experimental values.
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