• 열처리공학회지
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• 제14권3호
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• pp.160-166
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• 2001

The change of ribbon geometry, microstructure and shape recovery with Mn contents, wheel speed and various annealing temperature have been studied in Fe-X%Mn-5Cr-5Co-4Si (X%=15, 20, 24) shape memory alloy (SMA) ribbons rapidly solidfied by single roll chill-block melt-spinning process. The thickness and width of melt-spun ribbons are reduced, results in refining and uniformalizing grains with increasing wheel speed. In the ribbons melt-spun at a wheel speed of 15m/sec, both ${\varepsilon}$ and ${\alpha}^{\prime}$martensites are formed in ribbon 1 (15.5wt%Mn), while only ${\varepsilon}$ martensite is revealed in ribbon 2 (20.2wt%Mn) and ribbon 3 (23.5wt%Mn). The volume fraction of ${\varepsilon}$ martensite is decreased with increasing Mn contents, and those of ${\varepsilon}$ as well ${\alpha}^{\prime}$martensites are increased due to thermal stress relief and grain growth with increasing annealing temperature. Ms temperatures of the ribbons 1, 2 and 3 are fallen with increasing Mn contents. $M_s$ temperatures of the ribbons 1, 2 and 3 annealed at $300^{\circ}C$ for 3 min are risen abruptly, but are nearly constant even at higher annealing temperature, i.e., 400, 500 and $600^{\circ}C$ for 3 min. Shape recovery of the ribbons 1, 2 and 3 increased 30%, 52% and 69% with Mn contents, respectively. Shape recovery of ribbon 1 (15.5wt%Mn) formed ${\varepsilon}$ and ${\alpha}^{\prime}$martensites decreased because of the presence of ${\alpha}^{\prime}$martensite but those of ribbon 2 (20.2wt%Mn) and ribbon 3 (23.5wt%Mn) formed ${\varepsilon}$ martensite increased with increasing annealing temperature.

• 대한토목학회논문집
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• 제43권4호
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• pp.413-420
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• 2023

지진피해 감소를 위한 내진 구조 중에서 제진 구조는 댐퍼의 간단한 적용으로 효율적으로 내진 성능을 향상시키고 경제성을 확보할 수 있는 기술이다. 그러나 기존의 댐퍼는 요구 내진 성능과 재료 소성으로 인한 내구성에 대하여 한계를 나타낸다. 따라서 본 연구에서는 기본적으로 탄성 특성을 나타내는 폴리우레탄에 선행 압축을 가하고 초탄성 형상기억합금을 적용하여 복원 특성을 증진시킨 폴리우레탄 댐퍼를 제안하였다. 폴리우레탄 댐퍼의 특성을 검증하기 위하여 우선 개념을 정립하고 초탄성 형상기억합금과 강재 적용, 선행압축 크기를 설계 변수로 선정하여 설계 상세를 완성하였다. 또한, 구조 실험을 수행하여 응답 거동을 도출하여 하중 저항 성능, 잔류 변위, 회복률, 에너지 소산 능력을 분석하였다. 분석한 결과 폴리우레탄 댐퍼는 초탄성 형상기억합금 와이어를 적용하고 선행 압축이 증가하면 다양한 성능이 향상되는 결과를 나타냈다.

• 정보저장시스템학회논문집
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• 제11권2호
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• pp.36-40
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• 2015

The demand for flexible devices including solar cells, memories and batteries has increased rapidly over the past decades. In most flexible devices, polymer-based materials are used to enable the mechanical deformations such as bending or folding. Shape Memory Polymers (SMPs) is a high molecular compound polymer with flexibility and shape recovery characteristics. In this work, flexible shape memory device was fabricated by simply coating the conducting material, carbon nano-tube (CNT), on a shape memory polymer. Furthermore, durability of the device under various type of mechanical deformations was assessed. It is believed that the result of this work will aid in realization of a stretchable and wearable electronic device for practical applications.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.278-281
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• 2004

In this paper, the thermomechanical responses of shape memory alloy (SMA) actuators and their applications as the shape adaptive structures combining SMA actuators produced in the form of strip with composite structures are investigated. The numerical algorithm of the 3-D SMA thermomechanical constitutive equations based on Lagoudas model is implemented to analyze the unique characteristics of SMA strip. Also, the incremental SMA constitutive equations are implemented in the user subroutine UMAT by using ABAQUS finite element program. The shape change of structure is caused by initially strained SMA strip bonded on the surface of the composite structure when thermally activated. Numerical results show that SMA strip actuator can generate enough recovery force to deform the composite structure and sustain the deformed shape subjected to large external load, simultaneously.

• 한국안전학회지
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• 제29권4호
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• pp.28-33
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• 2014

Recently, the actuator worked by the driving recovery-force of the thermo elastic martensitic transformation of shape memory alloys(SMA) has been studied. This paper presents a study on the fatigue life of shape memory alloy (SMA) actuators undergoing thermally induced martensitic phase transformation under various stress levels. shape memory recoverable stress and strain of Ti-44.5at.%Ni-8at.%Cu alloys were by means of constant temperature tensile tests. Differential scanning calorimetry (DSC) was employed in order to investigate the transformation characteristics of the alloy before the tests. the results were summarized as follows. The martensite inducing stress incerased with the increasing of the Cu-contents. The fatigue life decreased with the increasing of the test load and the Cu-content. The data acquired will be very useful during the design process of an SMA NiTiCu element as a functional part of an actuator.

• 한국재료학회지
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• 제21권11호
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• pp.617-622
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• 2011

The effect of oxygen on the shape memory characteristics in Ti-18Nb-6Zr-XO (X = 0-1.5 at%) biomedical alloys was investigated by tensile tests. The alloys were fabricated by an arc melting method at Ar atmosphere. The ingots were cold-rolled to 0.45 mm with a reduction up to 95% in thickness. After severe cold-rolling, the plate was solution-treated at 1173 K for 1.8 ks. The fracture stress of the solution-treated specimens increased from 450 Mpa to 880 MPa with an increasing oxygen content up to 1.5%. The fracture stress increased by 287MPa with 1 at% increase of oxygen content. The critical stress for slip increased from 430 MPa to 695 MPa with an increasing oxygen content up to 1.5 at%. The maximum recovery strain of 4.1% was obtained in the Ti-18Nb-6Zr-0.5O (at%) alloy. The martensitic transformation temperature decreased by 140 K with a 1.0 at% increase in O content, which is lower than that of Ti-22Nb-(0-2.0)O (at%) by 20 K. This may have been caused by the effect of the addition of Zr. This study confirmed that addition of oxygen to the Ti-Nb-Zr alloy increases the critical stress for slip due to solid solution hardening without being detrimental to the maximum recovery strain.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.811-814
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• 2002

Using a mathematical theory, we show that the optimality condition of a turbulent diffuser with maximum pressure recovery at the exit is zero shear stress along the wall. The optimal diffuser shape is designed through iterative procedures by using the $k-{\varepsilon}-{\nu}^{2}-f$ turbulence model for flow simulation. The Reynolds number based on the bulk mean velocity and the channel height at the diffuser entrance is 18,000. We also perform large eddy simulation to validate the shape design results and investigate the flow characteristics near the zero-skin friction wall. Results from large eddy simulation show that the skin friction is slightly higher than zero but is still very small as compared to that of the flat plate boundary layer flow Although the time-averaged wall shear stress is slightly above zero along the diffuser wall, instantaneous flow reversals occur intermittently. The streamwise mein velocity shows an asymptotic behavior of the half-power-law near the wall where the skin friction is close to zero.

• 한국추진공학회지
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• 제6권2호
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• pp.65-74
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• 2002

전압력 회복율을 최대로 하기 위한 IRR형 램젯 공기 흡입구 초음속 확산부의 최적형상 설계를 수행하였다. 질량유량을 제약조건으로 고려하고 외부램프에서의 두 번째 경사충격파와 카울립 형상, 그리고 흡입구 목의 단면적을 설계변수로 선택하였다. 효율적인 최적화를 위해 설계변수 변환을 통한 개선된 반응면 기법을 사용하였으며 설계반복을 통해 높은 신뢰도의 반응면을 구성할 수 있었다. 최적화 기법으로 유전자 알고리즘을 사용하였으며, 이차원 Euler Code를 사용하여 공력해석을 수행하였다. 배압조건의 적용을 위해 흡입구 목 뒤로 가상의 노즐을 장착하였고 총 20회의 계산으로 종말충격파 이후의 전압력 회복율이 기준형상에 비하여 14% 향상된 초음속 확산부 최적형상을 설계할 수 있었다.

• 자원리싸이클링
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• 제11권2호
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• pp.28-35
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• 2002

충격형 분채기에 의한 폐프린트배선기판(PCBs)의 분쇄과정에서 일어나는 금속성분의 분쇄특성에 대한 연구가 수행되었다. PCBs로부터 금속성분들을 단체분리하기 위하여 -3 mm로 파쇄한 다음 충격형 분쇄기를 사용하여 분쇄하였으며 햄머의 회전속도가 금속성분의 분쇄에 미치는 영향을 관찰하였다. 동과 땜납 등과 같은 금속성분들의 입도분포 및 단체분리도를 조사하였다. 경사진동판을 사용하는 PCBs 분쇄물로부터 금속입자들의 형상분리에서 햄머의 회전속도와 입자크기가 미치는 영향을 검토하였다 61.3 m/s 햄머속도에서 동 성분은 +297$\mu$m 입자가 80% 이었지만 땜납성분은 -297$\mu$m 입자가 90%에 달했다. 형상분리법에 의한 금속입자의분리 시 햄머의 회전속도가 클수록 회수위치가 짧았으며 +297 $\mu$m 입자의 회수위치가 -297~+149$\mu$m 입자보다 짧았다. 회수위치가 짧을수록 금속입자의 구형도가 좋았으며 KI 값은 KI=1 로 증가하고, $\phi_{c}$ 값은 $\phi_{c}$ =1로 감소하였다.

• 패션비즈니스
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• 제22권4호
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• pp.93-105
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• 2018

Using FDM 3D printing, yarn shape and composition were modeled and 3D printed with PLA and TPU filaments currently used for apparel. Based on this, mechanical characteristics were measured to determine 3D printing yarn according to type of filaments in the 3D printed output and deformation and recovery characteristics due to differences in structure type. As a result of examining tensile and shear characteristics of PLA and TPU 3D printing compiles, TPU overall was measured with significantly lower stress than PLA. This is due to high elasticity of TPU's character, revealing that it has better flexibility than PLA. In addition, during deformation due to external forces, the more freedom between the head and foot parts of the loop, and the lower the force associated with each other, the more flexible it is. TPU revealed that it was easier to tension and recovery from tensile deformation than PLA, indicating potential for clothing materials using 3D printing. If high-molecular materials, such as PLA flexibility, it is likely to provide some flexibility through development of styles, including degree of freedom in modeling. Based on this, we provide basic data for developing 3D printing textures that can be satisfied with textile for apparel.