Experimental Research on Mechanical Properties of a New TiNi Shape Memory Alloy

Transcription

1 Key Engineering Materials Online: ISSN: , Vols , pp doi:.428/ 24 Trans Tech Publications, Switzerland Experimental Research on Mechanical Properties of a New TiNi Shape Memory Alloy Atsuo Hayashi, a, Masataka Tokuda, b, Tadashi Inaba,c and Kengo Hashimoto,d Department of Mechanical Engineering, Mie University, Kamihama 55, Tsu , Japan a hayashi@vivi.mach.mie-u.ac.jp, b tokuda@mach.mie-u.ac.jp, c inaba@mach.mie-u.ac.jp, d hasimoto@vivi.mach.mie-u.ac.jp Keywords: Shape Memory Alloy, TiNi, Sintering-powder Technology, Thin-walled Tube Experiment, Tension/Torsion/Compression Abstract. The shape memory alloy with a shape memory property and pseudo-elastic property has been noted as one of the most attractive smart materials. Especially, the TiNi shape memory alloy shows the high performance compared to other shape memory materials, and has additional excellent properties, for example, anti-erosion property, anti-abrasion property, anti-vibration property and so on. In these days, the Ti-Ni shape memory alloy has been applied in the engineering/industrial field. However, it is rather difficult to produce the homogeneous bulk material, and thus the provided TiNi shape memory material is mainly wire or plate, and thus its application is quite limited (for example, the antenna of mobile telephone, frame of eye-glasses and so on). Recently, our joint research group (university and industry) developed a new technology to produce the homogeneous bulk TiNi shape memory alloy by applying a sintering-powder technology. By using this technology, arbitrary shape of Ti-Ni shape memory material can be obtained in a high quality. In our laboratory, the thermo-mechanical property was confirmed experimentally, by using several loading processes: tension, compression, torsion, and combined loading process of thin-walled tube specimen. In this paper, the results are shown and discussed. Introduction Shape memory alloys have been expected from a viewpoint of engineering applications because of its unique mechanical properties, that is, the shape memory property and pseudo-elastic property [-]. Thus, the related research-and-development has been actively continued. However, almost all research works on the properties of the shape memory alloys were limited to some simple loading conditions, for example, the uni-axial tension [4]. On the other hand, the deformation mechanism of shape memory alloys is the solid-solid phase transformation so-called martensitic phase transformation, which is controlled by seven parameters as follows: six independent components of stress tensor and temperature [5-7]. It means that the two- or three-dimensional complicated deformations of shape memory alloys are expected under the complex loading conditions. Such deformations may be useful as the components of smart structures or intelligent materials systems. The systematic experiments and theoretical research are required to obtain a more profound knowledge on shape memory behavior under the complex loading conditions [8]. From above-mentioned point of view, in this study, the pseudo-elastic deformations of Ti-Ni shape memory alloy tube manufactured by the sintering synthetic method are experimentally investigated under the uni-axial tension, simple torsion, and uni-axial compression loading conditions. The obtained results are presented and discussed in this paper. Material and Experimental Method The material used in the experiment is TiNi based shape memory alloy whose chemical composition is Ti-56wt%Ni. The geometry of specimen is a thin-walled tube whose outer diameter is 7mm, inner All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (#69859, Pennsylvania State University, University Park, USA-8/9/6,6:2:5)

2 9 Advances in Engineering Plasticity and Its Applications diameter is 5 mm, thickness is mm, and length is mm. This specimen was manufactured by the sintering synthetic method. This new manufacturing technique has a special advantage to produce some arbitrary shape bulk TiNi material. The heat treatment to obtain the shape memory property is T = 54 heating for minutes in the argon gas and rapid cooling with ice-cold water. The characteristic temperatures measured by the DSC technique under stress-free condition (refer with Fig. ) are as follows: Ms = -2, Mf = -8, As = -8 Af =, where Ms and Mf are the martensitic phase transformation starting and finishing temperatures, respectively, and As and Af are the reverse phase transformation starting and finishing temperatures, respectively. Therefore, this material shows the pseudo-elastic behavior at room temperature. The experiments were conducted at room temperature as well as several different temperatures. The experimental apparatus used in this study is the multi axial loading testing machine (Shimadzu Auto-graph AG-TC). The grip device shown in Fig. 2 was used in the experiment. The grip device was set to the position of 5 mm of both ends of the specimen. Therefore, the gauge length was mm. Mf = -8 Cooling Ms = -2 Heat flow Heating As = -8 Af= Temperature ( ) Fig. DSC measurement result φ Fig. 2 Geometry of specimen and grip device

3 Key Engineering Materials Vols Experimental Results and Discussions Figure shows the stress-strain relations obtained by the loading-unloading tests of the uni-axial tension, the simple torsion and the uni-axial compression at the temperature T=28. As found from Fig., this material produced by the new manufacturing technique shows beautiful pseudo-elastic behavior in these three different loadings. Figure 4 shows the stress-strain relations obtained by the uni-axial tension, the simple torsion and the uni-axial compression at several different temperatures. As found from Fig. 4, this material was confirmed to deform in a shape memory manner at lower temperature and deform in a pseudo-elastic manner at the higher temperature. Figure 5 shows the phase-transformation stress-temperature diagram obtained on the basis of data shown in Fig. 4. As found from Fig. 5, these characteristic stresses depend linearly on the temperature as predicted by the thermodynamic theory in the uni-axial tension, the simple torsion as well as the uni-axial compression. Moreover, the difference of these characteristic (phase transformation) stresses between the uni-axial tension, the simple torsion and the uni-axial compression are quite small. This fact shows that the von-mises criterion is useful for the evaluation of these stresses. In order to confirm this tendency, some proportional loading tests were performed by the means of applying the combined loads of axial force and torque to the thin-walled tube specimen. Figure 6 shows one example of complex loading test. Figure 6(a) shows three kind of stress path given to the thin-walled tube specimen. Figure 6(b) shows the strain responses while loading. Figure 6(c) shows the strain responses while unloading. The strong path dependency is observed clearly Axial stress σ (MPa) Shear stress τ (MPa) Axial stress σ (MPa) Axial strain ε (%) Shear strain γ (%) Axial strain ε (%) Fig. Stress-strain relations for simple loading at the room temperature

4 92 Advances in Engineering Plasticity and Its Applications Stress σ(mpa) Tension Stress τ(mpa) Stress σ (MPa) Strain ε (%) Strain γ (%) Torsion Compression Strain ε (%) Fig. 4 Stress-strain relations at the different temperatures 5 4 tension torsion compression σ Ms Stress (MPa) 2 σ As σ Af Temp.( ) Fig. 5 Phase transformation stress-temperature diagram

5 Key Engineering Materials Vols Shear stress γ (MPa) 247 C 45 σeq=5 MPa B 2 A 247 Axial stress σ (MPa) (a) Stress path Shear strain / γ(%) γ / [ %] 2 C A ε [%] B B B 2 Axial strain ε (%) (b) Strain responce while loading γ / [% ] Shear strain / γ(%) 2 C ε [%] B B B 2 Axial strain ε (%) A (c) Strain responce while unloading Fig. 6 An example of complex loading test

6 94 Advances in Engineering Plasticity and Its Applications Conclusions In this study, the pseudo-elastic deformations of TiNi shape memory alloy tube manufactured by the sintering synthetic method were experimentally investigated under the uni-axial tension, the simple torsion, the uni-axial compression, and some complex loading conditions. In the results, several interesting and fundamental thermo-mechanical behaviors of TiNi alloy are confirmed. Further systematic experiments and theoretical research on the shape memory behavior under complex loading conditions are expected for engineering application of shape memory alloy. References [] K. Tanaka and F. Nishimura, Metals and Materials, Vol.4, No. (998), pp [2] H. Funakubo, Shape memory alloy (in Japanese), Sangyo-tosho (984). [] T.J. Lim and D.L. McDowell, Journal of Intelligent Material Systems and Structures, Vol.6 (995), pp [4] E.J. Graesser and F.A.Cozzarelli, Journal of Intelligent Material Systems and Structures, Vol.5 (994), pp [5] S. Miyazaki, T. Sakuma and T. Shibuya, Characteristics and Applications of Shape Memory Alloys (in Japanese), CMC (2). [6] P. Sittner and M.Tokuda, Journal of the Society of Materials Science (in Japanese), Vol.44, No.5 (995), pp [7] P. Sittner, M. Tokuda, M. Takakura and M. Ye, Materials Science Research International, Vol., No.4 (995), pp [8] M. Tokuda, M. Haze, M. Ye, B. Bundara and P. Sittner, Proc. of the Japan-France Seminar on Intelligent Materials and Structures (997), pp