Papers by Keyword: Shape Memory Effects (SME)

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Authors: Jin Kyung Lee, Young Chul Park, Sang Ll Lee, Joon Hyun Lee, Jong Baek Lee
Abstract: Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite (MMC). TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress using shape memory effect in the matrix. A hot press method was used to create the optimal condition for the fabrication of shape memory alloy (SMA) composite. The bonding effect between the matrix and the reinforcement within the SMA composite was strengthened by the cold rolling. The fabricated composite by these processes can be applied as a part of the aircraft, and this part is operated under severe flying condition such as low temperature and high pressure. In this study, an acoustic emission technique was used to quantify the microscopic damage behavior of cold rolled TiNi/Al6061 SMA composite at low temperature condition. The results showed that the tensile strength of the TiNi/Al6061 SMA composite increased with the TiNi reinforcement at low temperature condition, but the strength for the specimen subjected to the cold rolling decreased. AE parameters of AE counts, amplitude and energy were useful to evaluate the microscopic damage behavior of the composite.
Authors: Li Na Bai, Gui Xing Zheng, Jing Xin, Jian Jun Zhang
Abstract: The influences of Gd concentration on martensitic transformation and magnetic properties of NiMnIn alloys were investigated by differential scanning calorimetry (DSC) , vibrating sample magnetometry (VSM), X-ray diffraction (XRD) and etc. It shows that addition of Gd enhances martensite transition temperature and that X-ray diffraction analysis of experimental alloys is revealed which the mixture is martensite and austenite at room temperature. These alloys show promise as a metamagnetic shape memory alloy with magnetic-field-induced shape memory effect.
Authors: Koichi Tsuchiya, O. Kawabata, Minoru Umemoto, H. Sato, K. Marukawa
Authors: Hirohisa Tamagawa
Abstract: A polymer fabricated by mixing PU soft segment and epoxy bore the thermal characteristics of the melting temperature, Tm, of PU soft segment and the glass transition temperature, Tg, of epoxy. The polymer fabricated even exhibited the shape memory effect at the Tg and Tm. Based on this observation, it was speculated that simply mixing two polymers bearing totally different thermal characteristics each other could result in a two-stage SMP, which could exhibit the shape memory effect at the two distinct temperatures. However, it was actually observed that the two-stage SMP was not always successfully created by that method. But DSC measurements revealed that such an unsuccessfully fabricated SMP still bore the thermal characteristics of its ingredient polymers. Hence, the mixing of appropriate polymers still could result in a new two-stage SMP, and the method of two-polymer-mixing must be still an effective method for creating a two-stage SMP.
Authors: Wei Wang, Shi Yan, Gang Bing Song, Li Jiao
Abstract: An improved two-dimensional constitutive model for shape memory alloys (SMAs), which can describe both the shape memory effect (SME) and super elasticity effect (SE) of the SMAs, is developed in the paper based on the previous work of Boyd and Lagoudas, who used the thermodynamics theories of free energy and dissipation energy to derive the constitutive law of the SMAs. The improved model, which will combine the ideas of Brinsion’s one-dimensional constitutive law and the concepts of Boyd and Lagoudas’ two-dimensional one, has a simple but accurate expression. Two examples are used to numerically validate the efficiency of the improved model and the results of the simulations show that the developed constitutive model can qualitatively describe the thermo-mechanical behaviors of two-dimensional SMAs.
Authors: Bohong Jiang, Xuan Qi, Y. Ren, Cheng Ming Wang
Authors: Hong Gun Kim, H.K. Noh, Young Tae Cho, J.Y. Kim, S.K. Park, Dong Joo Lee
Authors: Junpei Sakurai, Yuko Aono, Yui Ishida, Seiichi Hata
Abstract: We investigated characteristics of Ti-Ni-Zr amorphous thin films before and after annealing, in order to search for novel Ti-Ni-Zr thin film metallic glasses (TFMGs) that exhibit a shape memory effect after crystallization. We found that the Ti42Ni47Zr11 TFMG exhibited a stable shape memory effect after crystallization. This alloy showed a glass transition with the glass transition and crystallization temperatures of 703 and 760 K, respectively. Moreover, this alloy showed a one-step martensitic phase transformation of B2 to B19', when annealed at 973 K for 3.6 ks. The martensitic phase start temperature and reverse martensitic phase start temperature were 296 and 352 K, respectively. In addition, this alloy showed a recovery strain of about 2.4%.
Authors: Abdul Wadood, Tomonari Inamura, Hideki Hosoda, Shuichi Miyazaki
Abstract: In order to develop new nickel-free biomedical Ti-based alloys, effect of silver additions on mechanical properties of Ti-5Cr (mol%) alloy was investigated. Cold workability of Ti-5Cr alloy was 5% in thickness reduction and the cold rolling reduction was improved to be 38% by 2mol% Ag addition and 96% by 4mol%Ag addition. The improvement was due to β phase stabilization. From the XRD results, α’ martensite was the dominant phase in Ti-5Cr-2Ag alloy and β phase was the dominant phase in Ti-5Cr-4Ag alloy. By tensile tests, Ti-5Cr-4Ag alloy showed good strength of 447 MPa in ultimate tensile strength (UTS) and ductility of 13% in fracture strain. Ti-5Cr-4Ag showed higher hardness of HV398 than Ti-5Cr-2Ag with HV288. The hardening by increase of Ag is probably due to the solid solution strengthening. By the cyclic loading-unloading tensile tests with a constant strain increment, Ti-5Cr-4Ag showed pseoudoelastic behavior. Ti-5Cr-4Ag also showed shape memory effect with 57% in shape recovery ratio. It is concluded that Ti-5Cr-4Ag is hopeful as a new non-allergic shape memory material for biomedical applications.
Authors: Devendra Gupta, David S. Lieberman
Abstract: The Au-Cd alloys continue to be important vehicles of research for the shape memory effect involving martensitic transformations and related phenomena.They transform to a variety of martensitic structures depending on the alloy composition and thermal history. Additionally, the Au-rich alloys display rubber like behavior involving thermo-elastic memory. Defects and diffusion play important roles in determining these properties. Defects and diffusion mechanisms in the Au- 47.5 - 50.5 at.% Cd alloys are examined. Diffusion in the nanometer regime and the states of defects are found to be important contributing factors to determine the shape memory effect, the variable martensitic transformations and the rubber like behavior, which are discussed in details.
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