• 한국안전학회지
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• 제24권1호
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• pp.26-30
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• 2009

Shape memory recoverable stress and strain of Ti-42.5at%Ni-10at%Cu alloys were measured by means of constant temperature tensile tests. The alloys' transformation behavior is B2 - B19 by DSC result. The strain by tensile stress were perfectly recovered by heating at any testing conditions but shape memory recoverable stress increased to 66MPa and then slightly decreased. Transformation temperatures from thermal cycling under constant uniaxial applied tensile loads linearly increased by increasing tensile load and their thermal hysteresis are about 110K and their maximum recoverable strain is 6.5% at 100MPa condition.

• 대한심미치과학회지
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• 제3권1호
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• pp.32-43
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• 1995

Ni-Ti alloy has excellent corrosion resistance, biocompatibility, shape memory effect and superelasticity, so it has been used widely in biomedical fields. But it has difficulty in casting due to its high melting temperature and oxygen affinity at high temperature. Recently it has been attempted to cast Ni-Ti alloy using new casting machine and investment. The purpose of this study was to examine the superelastic behavior of cast shape memory Ni-Ti alloy and to compare the mechanical properties of the cast shape memory alloy with those of commercial alloys for removable partial denture framework. Ni-Ti alloy(Ni 50.25%, Ti 49.75% : atomic ratio) was cast with dental argon-arc pressure casting machine and Type IV gold alloy, Co-Cr alloy, Ni-Cr alloy, pure titanium were cast as reference. Experimental cast Ni-Ti alloy was treated with heat($500{\pm}2^{\circ}C$) in muffle furnace for 1 hour. Transformation temperature range of cast Ni-Ti alloy was measured with differential scanning calorimetry. The superelastic behavior and mechanical properties of cat Ni-Ti alloy were observed and evaluated by three point bending test, ultimate tensile test, Vickers microhardness test and scanning electron microscope. The results were as follows : 1. Cast Ni-Ti alloy(Ni 50.25%, Ti 49.75% : atomic ratio) was found to have superelastic behavior. 2. Stiffness of cast Ni-Ti alloy was considerably lesser than that of commercial alloys for removable partial denture. 3. Permanent deformation was observed in commercial alloys for removable partial denture framework at three point bending test over proportional limit(1.5mm deflection), but was not nearly observed in cast Ni-Ti alloy. 4. On the mechanical properties of ultimate tensile strength, elongation and Vickers microhardness number, cast Ni-Ti alloy was similiar to Type IV gold alloy, Co-Cr alloy, Ni-Cr alloy and pure titanium. With these results, cast Ni-Ti alloy had superelastic behavior and low stiffness. Therefore, it is suggested that cast Ni-Ti alloy may be applicated to base metal alloy for removable partial denture framework.

• Structural Engineering and Mechanics
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• 제68권5호
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• pp.519-526
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• 2018

In this article, experimental training of the commercial available shape memory alloy fibre (SMA) fibre under the combined thermomechanical loading is reported. SMA has the ability to sense a small change in temperature (${\geq}10^{\circ}C$) and activated under the external loading and results in shape change. The thermomechanical characteristics of SMA at different temperature and mechanical loading are obtained through an own lab-scale experimental setup. The analysis is conducted for two types of the medium using the liquid nitrogen (cold cycle) and the hot water (heat cycle). The experimental data indicate that SMA act as a normal wire for Martensite phase and activated behavior i.e., regain the original shape during the Austenite phase only. To improve the confidence of such kind of behavior has been verified by inspecting the composition of the wire. The study reveals interesting conclusion i.e., while SMA deviates from the equiatomic structure or consist of foreign materials (carbon and oxygen) except nickel and titanium may affect the phase transformation temperature which shifted the activation phase temperature. Also, the grain structure distortion of SMA wire has been examined via the scanning electron microscope after the thermomechanical cycle loading and discussed in details.

• 한국정밀공학회지
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• 제19권2호
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• pp.72-78
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• 2002

Thermomechanical behavior and mechanical properties of A16061 matrix composite with shape memory alloy(SMA) fiber are studied by using fnite element analysis(FEA). The smartness of the SMA is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when healed after being prestrained. In this paper, an analytical model is assumed two dimentional axisymetric model of one fiber and around the matrix. To evaluate the strength of composite usig FEM, the concept of smart composite was simulated on computer. The Shape memory effect(SME) simulation is very difficult using FEM because of the nonlinear analysis and the elastic plastic analysis. Thus, in this paper, the FEA was carried out at two critical temperature conditions; room temperature and high temperature(363K). The analysis is compare the finite element analysis result with the test result for the analysis validity.

• Elastomers and Composites
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• 제42권4호
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• pp.217-223
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• 2007

결정성을 갖는 에틸렌프로필렌디엔 고무($Nordel^{(R)}$ IP)를 과산화물로 가교시키고 열적, 기계적특성과 형상기억거동을 조사하였다. 겔함량 측정결과 가교도는 DCP 함량에 따라 증가되었으며, DSC 분석결과 가교된 고무는 결정상이 존재하고 있음을 알 수 있었다. 인장시험 결과가교도가 증가함에 따라 고무의 모듈러스는 증가되며 파단신율은 감소되었다. 이와 같이 가교구조 내에 결정상을 함유하는 고무는 우수한 형상기억 특성을 나타내었다. 즉, 이러한 고무는 결정상의 용융온도 이상에서 쉽게 원하는 형태로 변형되고, 변형된 상태에서 냉각시키면 변형된 형태로 잘 고정되었으며, 또한 이렇게 변형된 형상의 시료를 용융온도 이상으로 가열하면 원래의 모양으로 신속히 되돌아오는 것을 관찰할 수 있었다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.825-828
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• 2005

In this paper, we propose a new nonvolatile unit memory cell and proposal peripheral circuit using the polymer material. Memory that relies on bistable behavior- having tow states associated with different resistances at the same applied voltage - has attracted much interest because of its nonvolatile properties. Such memory may also have other merits, including simplicity of structure and manufacturing, and the small size of memory cells. We have plotted the load line graphs for the use of a polymer memory character, hence we have designed in the band-gap reference shape of a write/erase drive, and then designed in the 2-stage differential amplifier shape of a sense amplifier in the consideration of a low current characteristic of a polymer memory cell. The simulation result shows that is has high gain about 80dB by sensing the very small current.

• 비파괴검사학회지
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• 제21권6호
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• pp.634-641
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• 2001

형상기억복합재료는 복합재료내에 압축잔류응력을 발생시킴으로써 재료의 인장강도를 증가시키는데 사용되어 지고 있다. 본 연구에서는 형상기억복합재료를 제조하기 위하여 TiNi 강화재와 A16061 기지재를 사용하였으며 핫프레스 방법에 의해 TiNi/A16061 형상기억복합재료를 제조하였다. 그러나 핫 프레스 방법에 의해 제조된 형상기억복합재료는 하중을 받을 시 강화재와 기지재 사이에 계면손상현상이 발생하였으며 이를 위하여 내간압연을 실시하였다. 냉간압연을 받은 시험편은 냉간압연을 받지 않은 시험편에 비하여 인장강도가 현저히 증가하였다. 또한 본 연구에서는 고온에서 형상기억복합재료의 미시적 손상을 평가하기 위하여 음향방출기법을 이용하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제22권3호
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• pp.103-110
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• 2018

표면매립공법으로 매립한 철계-형상기억합금으로 보강한 보의 휨 거동을 장기 하중 재하실험을 통해 평가하였다. 철계-형상기억합금 길이대비 2%와 4%의 사전변형 및 형상기억효과 활성화에 의한 프리스트레스 하중 도입을 실험변수로 설정하였다. 1 tonf의 콘크리트 추를 보 중앙에 거치한 후 6개월간의 보 중앙부의 장기 처짐을 측정하였다. 실험결과, 철계-형상기억합금으로 보강한 보의 휨 강성이 증대되었으며, 사전변형이 증가할수록 보강재의 강성감소로 인한 처짐이 증가하는 것으로 나타났다. 프리스트레스 하중 도입에 따른 처짐을 비교했을 때, 프리스트레스 하중을 도입하지 않은 실험체에 비해, 프리스트레스 하중을 도입한 실험체는 약 30%의 처짐 감소 효과를 보이는 것으로 나타났다.

• 도시과학
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• 제7권1호
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• pp.5-9
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• 2018

The nickel-titanium shape memory alloy (SMA), referred to as Nitinol, exhibits a superelastic effect that can be restored to its original shape even if a significant amount of deformation is applied at room temperature, without any additional heat treatment after removal of the load. Owing to these unique material characteristics, it has widely used as displacement control devices for seismic retrofitting in civil engineering fields as well as medical, electrical, electronic and mechanical fields. Contrary to ordinarty carbon steel, superelastic SMAs are very resistant to fatigue, and have force-displacement properties depending on loading speed. The change for the mechanical properties of superelastic SMAs are experimentally inviestigated in this study when loading cycle numbers and loading speeds are different. In addition, the standardized force-displacement properties of such superelastic SMAs are proposed with an aim to efficiently design the seismic retrofitting devices made of these materials.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.186-191
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• 2001

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). In this study, 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 in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 shape memory alloy(SMA) composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation and volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 SMA composite. In addition, two dimensional AE source location technique was applied to inspect the crack initiation and propagation in composite.