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홍기남 ( Ki-nam Hong ),연영모 ( Yeong-mo Yeon ),지상원 ( Sang-won Ji ) 한국구조물진단유지관리공학회 2020 한국구조물진단유지관리공학회 논문집 Vol.24 No.6
본 논문은 철계-형상기억합금(Fe-SMA) 바를 이용하여 제작된 콘크리트 보의 휨 거동 평가를 위한 실험적 연구이다. 실험을 위해 200mm×300mm × 2,200mm의 콘크리트 보를 제작하였으며 인장재로 4% 사전변형된 Fe-SMA 바를 사용하였다. 실험 변수로 인장재 종류(SD400, Fe-SMA), 철근 비(0.2, 0.39, 0.59, 0.78), Fe-SMA 활성화(활성화, 비활성화) 그리고 Fe-SMA bar 연결방법(미연결, 용접, 커플러)를 고려하였다. Fe-SMA 바를 활성화하기 위해 전기저항 가열 방법을 이용하여 5A/mm<sup>2</sup>의 전류를 실험체가 160℃에 도달할 때 까지 공급하였다. 캠버효과에 의한 실험체의 상향 변위가 안정되면 2,000kN 용량의 엑츄레이터를 이용하여 3점 휨 재하 실험을 실시하였다. 실험결과 Fe-SMA 바를 활성화 함에 따라 캠버효과에 의해 상향 변위가 발생하는 것으로 나타났다. Fe-SMA 바를 활성화한 실험체는 활성화하지 않은 실험체에 비해 더 높은 하중에서 초기균열이 발생하였다. 그러나 일반적인 프리스트레스 콘크리트와 동일하게 Fe-SMA 활성화에 따른 프리스트레스 도입이 보의 극한 상태에 미치는 영향은 미미한 것으로 나타났다. This paper reports an experimental study to evaluate the flexural behavior of concrete beams reinforced using Fe based shape memory alloy (Fe-SMA) bars. For the experiment, a concrete beam of 200mm×300mm×2,200mm was produced, and a 4% pre-strained Fe-SMA bar was used as a tensile reinforcement. As experimental variables, type of tensile reinforcement (SD400, Fe-SMA), reinforcement ratio (0.2, 0.39, 0.59, 0.78), activation of Fe-SMA (activation, non-activation), and joint method of Fe-SMA bar (Continuous, welding, coupler) were considered. The electric resistance heating method was used to activate the Fe-SMA bar, and a current of 5A/mm<sup>2</sup> was supplied until the specimen reached 160°C. After the upward displacement of the specimen due to the camber effect was stabilized, a three-point flexural loading experiment was performed using an actuator of 2,000 kN capacity. As a result of the experiment, it was found that the upward displacement occurred due to the camber effect as the Fe-SMA bar was activated. The specimen that activated the Fe-SMA bar had an initial crack at a higher load than the specimen that did not activate it. However, as with general prestressed concrete, the effect of the prestress by Fe-SMA activation on the ultimate state of the beam was insignificant.
Fe-Mn계 합금에서 응력유기 ε 마르텐사이트의 양에 미치는 열처리 온도의 영향
지광구 ( K. K. Jee ),한주현 ( J. H. Han ),장우양 ( W. Y. Jang ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.6
N/A In this work, a new method of measuring volume fraction of deformation-induced ε martensite is pro-posed using endothermic heat on reverse transformation. As grain size increases, the amount of ε martensite forming on cooling increases. However, with a decrease in grain size, more ε is induced by deformation, improving shape memory effect.
Xiaochen Liu,Peng Xu,Like Yao,Xiang Li,Chi Pang,Long Yang,Yi Liang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.10
Laser cladding technology was adapted to fabricate Fe-based shape memory alloy/Nb composite coatings with 5 wt. % Nb doping amounts on 304 stainless steel to promote the microhardness and wear resistance. The SEM, XRD, optical profilometer and electrochemical workstation were used to characterize micromorphology, phase and microstructure. Meanwhile, wear and anti-resistance ability were detected. The results showed that Nb, NbC, ε-martensite, α’-martensite and γ-austenite were found in SMA/Nb coating. The microhardness was enhanced because of the solid solution strengthening and second phase strengthening. Also, the shape recovery rate and anti-corrosion property of the SMA/Nb coating are improved as well.
Creep and stress relaxation of a FeMnSi-based shape memory alloy at low temperatures
Leinenbach, C.,Lee, W.J.,Lis, A.,Arabi-Hashemi, A.,Cayron, C.,Weber, B. Elsevier Sequoia 2016 Materials science & engineering. properties, micro Vol.677 No.-
<P>The creep and stress relaxation behavior of a Fe-17Mn-5Si-10Cr-4Ni-1(V,C) (wt%) shape memory alloy at low homologous temperatures (-45 degrees C < T < 50 degrees C) was systematically studied in stress and strain controlled tensile tests. At constant stresses at -45 degrees C, the alloy exhibits pronounced creep up to 0.6% at 600 MPa after only 30 min holding time. If the strain is kept constant, a pronounced stress relaxation of up to 10% of the initial stress was observed. The final creep strains, the creep rates at a constant stress as well as the stress relaxation at a constant strain increase with decreasing temperature. In addition, the change of the recovery stress as a function of time in a restrained sample after 4% elongation and heating to different constant temperatures was monitored. It was observed that the increase of the final recovery stress is more pronounced when the holding temperature is increased. This behavior was explained with the time and temperature dependent formation of stress induced epsilon-martensite from the parent gamma-austenite phase during mechanical loading according to the model of Kajiwara et al. as well as with the increased number of stacking faults at lower temperatures, which serve as nucleation sites for the epsilon-martensite formation. (C) 2016 Elsevier B.V. All rights reserved.</P>