• Smart Structures and Systems
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• 제6권2호
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• pp.91-100
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• 2010

An experimental study was carried out to investigate the shape control of plates via embedded shape memory alloy (SMA) wires. An extensive body of literature proposes the use of SMA wires to actively modify the shape or stiffness of a structure; in most cases, however, the study focuses on modeling and little experimental data is available. In this work, a simple proof of concept specimen was built by attaching four prestrained SMA wires to one side of a carbon fiber laminate plate strip. The specimen was clamped at one end and tested in an environmental chamber, measuring the tip displacement and the SMA temperature. At heating, actuation of the SMA wires bends the plate; at cooling deformation is partially recovered. The specimen was actuated a few times between two fixed temperatures $T_c$ and $T_h$, whereas in the last actuation a temperature $T_f$ > $T_h$ was reached. Contrary to most model predictions, in the first actuation the transformation temperatures are significantly higher than in the following cycles, which are stable. Moreover, if the temperature $T_h$ is exceeded, two separate actuations occur during heating: the first follows the path of the stable cycles; the second, starting at $T_h$, is similar to the first cycle. An interpretation of the phenomenon is given using some differential scanning calorimeter (DSC) measurements. The observed behavior emphasizes the need to build a more comprehensive constitutive model able to include these effects.

• Steel and Composite Structures
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• 제28권1호
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• pp.83-98
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• 2018

This research was conducted to study the behavior of exterior concrete beam-column joints with reinforced shape memory alloy (SMA) bars tested under cyclic loading. These bars benefit from superelastic behavior and can stand high loads without residual strains. The experimental part of the study, 8 specimens of exterior concrete beam-column joints were made and tested. Two different types of concrete with 30 and 45 MPa were used. Four specimens contained SMA bars and 4 specimens contained steel bars in beam-column joints. Furthermore, different transverse reinforcements were used in beams investigate the effects of concrete confinement. Specimens were tested under cyclic loading. Results show that SMA bars are capable of recentering to their original shape after standing large displacements. Due to the superelastic behavior of SMA bars, cracks at the joint core vanish under cyclic loading. As the cyclic loading increased, bending failure occurred in the beam outside the joint core. In the analytical parts of the study, specimens were simulated using the SeismoStruct software. Experimental and analytical results showed a satisfactory correlation. Plastic hinge length at the beam joint for specimens with SMA and steel bars was calculated by empirical equations, experimental and analytical results. It was shown that Paulay's and Priestley's equations are appropriate for concrete beam-column joints in both types of bars.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 춘계학술대회 논문집
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• pp.1613-1618
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• 2007

Mechanical characteristics of composite materials containing NiTi shape memory alloy(SMA) have been analyzed in this study by conducting tensile, photo-elasticity and impact tests for the specimens. From the test results, the SMA composite materials can be considered as one of possible ways in detecting and controlling damages in the materials.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 춘계학술발표대회 논문집
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• pp.127-130
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• 2004

In this paper, active shape control of composite structure actuated by shape memory alloy (SMA) wires is presented. Hybrid composite structure was established by attaching SMA actuators on the surfaces of graphite/epoxy composite beam using bolt-joint connectors. SMA actuators were activated by phase transformation, which induced by temperature rising over austenite finish temperatures. In this paper, electrical resistive heating was applied to the hybrid composite structures to activate the SMA actuators. For faster and more accurate shape or deflection control of the hybrid composite structure, PID feedback controller was designed from numerical simulations and experimentally applied to the SMA actuators.

• 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.

• 한국정밀공학회지
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• 제30권1호
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• pp.47-52
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• 2013

In order to operate a search and rescue robot in hazardous area, the robot requires high mobility and adaptable locomotion for moving in unpredictable environments. In this paper, we propose the deformable soft wheel robot that can produce three kinds of driving modes; caterpillar driving mode, normal wheel driving mode, legged-wheel driving mode. The robot changes its driving mode as it faces the various obstacles such as a small gap, stairs etc. Soft film and composite materials are used for fabrication of deformable wheel structure and Shape Memory Alloy (SMA) coil spring actuators are attached on the structure as an artificial muscle. Film lamination and an composite manufacturing process is introduced and the robot design is required to be modified and compromised to applying the manufacturing process. The prototype is developed and tested for verifying feasibility of the deformable wheel locomotion.

• Composites Research
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• 제22권2호
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• pp.37-42
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• 2009

이 논문은 형상기억합금 선재를 이용한 굽힘 작동기의 실험적인 설계방법을 다루고 있다. 제안된 굽힘 작동기는 유리섬유 프리프레그를 이용하여 만든 스트립, 스프링 그리고 형상기억합금 선재로 구성된다. 굽힘 작동기에서 스트립은 초기에 형상기억합금 선재에 초기하중을 가하기 위하여 굽힘 형태로 정되며, 스프링은 형상기억합금 선재가 작동 후 빠른 시간내에 초기 형상으로 돌아오기 위한 보조수단으로 사용된다. 먼저 형상기억합금 선재의 특성을 알아보기 위하여 시차주사열량계(DSC)를 이용한 실험, 여러 종류의 초기 하중을 가한 후 작동 성능 실험, 인장 시험, 온도 변화에 따른 기계적 거동을 조사하였다 이를 바탕으로 스트립, 스프링, 인가 전압에 의한 영향을 관찰하고 소모전력을 분석하여 굽힘 작동기를 설계하였다. 특정 조건을 갖는 굽힘 작동기는 낮은 소모전력으로 빠른 응답성능을 나다내었다.

• Composites Research
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• 제18권2호
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• pp.38-45
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• 2005

본 연구에서는 시차주사열량분석장치와 X-선 회절장치를 이용하여 어닐링 열처리 조건에 따른 니티놀 형상기억합금의 상변환 특성과 결정구조를 조사하였다. 어닐링 열처리 조건으로는 열처리 시간과 열처리 온도를 고려하였으며 특히 열처리 시간은 5분. 15분, 30분, 45분 그리고 열처리 온도는 $400^{\circ}C,\;500^{\circ}C,\;525^{\circ}C,\;550^{\circ}C,\;575^{\circ}C,\;600^{\circ}C,\;700^{\circ}C,\;800^{\circ}C,\;and\;900^{\circ}C$를 적용하였다 연구결과에 따르면 열처리 시간과 열처리 온도 등의 어닐링 열처리 조건은 니티놀 형상기억합금의 상변환 특성과 결정구조에 큰 영향을 미침을 알 수 있었다.

• 센서학회지
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• 제7권4호
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• pp.285-292
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• 1998

형상기억합금은 액츄에이터로서의 우수한 특성으로 인해 공학의 많은 분야에서 사용되고 있다. 그 중의 한 예로서 복합재료 구조물에 삽입되어 지능형 복합재료 구조물의 작동소재로서 유용하게 사용될 수 있다. 형상기억합금 선의 전기저항은 변형률에 대하여 큰 영향을 받는데, 이를 이용하여 형상기억합금 선을 이들 물리량에 대한 센서로 활용할 수 있을 것이다. 따라서 본 연구에서는 복합재료 보에 삽입된 형상기억합금 액츄에이터의 센서로서의 활용 가능성을 연구 조사하여 이를 변위센서로 활용할 수 있음을 밝혔다.

• 대한기계학회논문집A
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• 제33권2호
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• pp.99-107
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• 2009

This study produced a design curve and fatigue limit for a variation in volume ratio and reduction ratio of TiNi/Al composites. In many cases, stress-life curve does not indicate fatigue limit, so it was presented by probabilistic-stress-life curve. Goodman diagram was used to analyze the fatigue strength of materials with a finite life determined by repeated load and the fatigue strength of endurance limit with an infinite life. The fatigue experiment was conducted using the scenk-type plane bending specimen in same shape. The result of the fatigue test, which had been conducted under consistent stress amplitude, was examined. (i) The optimal condition for TiNi/Al in accordance with hot pressing (ii) Impacts of fatigue limit caused by a variation in reduction ratio and volume ratio of TiNi/Al composites (iii) Probability distribution for fatigue limit of TiNi/Al2024 and TiNi/Al6061.