• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2001년도 하계학술대회 논문집
• /
• pp.323-326
• /
• 2001

NI$_2$MnGa-based ferromagnetic shape memory alloys (FSMA) are hoped to be used as robust actuators with high performance and power density, as a replacement of other actuation materials such as thermo-mechanical SMAs and mechanical-electric piezoelectrics. Recently, we have observed significant shape changes under magnetic field application when single- and poly-crystalline forms are used. In the present study, two mechanisms have been proposed to predict the magnetic field-induced shape change as a function of external magnetic field at temperatures below Mr and above Ar. In the case of the field-induced shape change at temperature below M$_{f}$, paired martensite variants are assumed to form by application of magnetic field. The direction of magnetization in martensites formed in austenite matrix is assumed to be parallel to the applied magnetic field in the case of shape change by application at temperature above Af. Various energies has been considered in the shape change under two mechanisms.s.

• 한국공간구조학회논문집
• /
• 제18권2호
• /
• pp.109-119
• /
• 2018

In this paper a systematic numerical analysis is performed to obtain the energy dissipation and re-centering capacities of diagonal steel braced frames subjected to cyclic loading. This diagonal steel bracing systems are fabricated with super-elastic SMA (Shape Memory Alloy) braces in order to develop a recentering seismic resistance system without residual deformation. The three-dimensional nonlinear finite element models are constructed to investigate the horizontal stiffness, drifts and failure modes of the re-centering bracing systems.

• Smart Structures and Systems
• /
• 제4권2호
• /
• pp.247-259
• /
• 2008

The potential use of Cu-based shape memory alloys (SMA) in retrofitting historical monuments is investigated in this paper. This study is part of the ongoing work conducted in Tunisia within the framework of the FP6 European Union project (WIND-CHIME) on the use of appropriate modern seismic protective systems in the conservation of Mediterranean historical buildings in earthquake-prone areas. The present investigation consists of a finite element simulation, as a preliminary to an experimental study where a cantilever masonry wall, representing a part of a historical monument, is subjected to monotonic and quasi-static cyclic loadings around a horizontal axis at the base level. The wall was retrofitted with an array of copper SMA wires with different cross-sectional areas. A new model is proposed for heat-treated copper SMAs and is validated based on published experimental results. A series of nonlinear finite element analyses are then performed on the wall for the purpose of assessing the SMA device retrofitting capabilities. Simulation results show an improvement of the wall response for the case of monotonic and quasi-static cyclic loadings.

• Structural Engineering and Mechanics
• /
• 제82권1호
• /
• pp.107-120
• /
• 2022

The bracing members capable of active control against seismic loads to reduce earthquake damage have been widely utilized in construction projects. Effectively reducing the structural damage caused by earthquake events, bracing systems equipped with retrofitting damper devices, which take advantage of the energy dissipation and impact absorption, have been widely used in practical construction sites. Shape Memory Alloys (SMAs) are a new generation of smart materials with the capability of recovering their predefined shape after experiencing a large strain. This is mainly due to the shape memory effects and the superelasticity of SMA. These properties make SMA an excellent alternative to be used in passive, semi-active, and active control systems in civil engineering applications. In this research, a new system in diagonal braces with slit damper combined with SMA is investigated. The diagonal element under the effect of tensile and compressive force turns to shear force in the slit damper and creates tension in the SMA. Therefore, by creating shear forces in the damper, it leads to yield and increases the energy absorption capacity of the system. The purpose of using SMA, in addition to increasing the stiffness and strength of the system, is to create reversibility for the system. According to the results, the highest capacity is related to the case where the ratio of the width of the middle section to the width of the end section (b₁/b) is 1.0 and the ratio of the height of the middle part to the total height of the damper (h₁/h) is 0.1. This is mainly because in this case, the damper section has the highest cross-section. In contrast, the lowest capacity is related to the case where b₁/b=0.1 and the ratio h₁/h=0.8.

• Smart Structures and Systems
• /
• 제3권1호
• /
• pp.89-114
• /
• 2007

Two aspects of the design of a small-scale smart wing are addressed in this work, related to the ability of the wing to modify its cross section assuming the shape of two different airfoils and to the possibility of deflecting the profiles near the trailing edge in order to obtain hingeless control surfaces. The actuation is provided by one-way shape memory alloy wires eventually coupled to springs, Shape Memory Alloys (SMAs) being among the most promising materials for this kind of applications. The points to be actuated along the profiles and the displacements to be imposed are selecetd so that they satisfactorily approximate the change from an airfoil to the other and to result in an adequate deflection of the control surface; the actuators and their performances are designed so that an adequate wing stiffness is guaranteed, in order to prevent excessive deformations and undesired airfoil shape variations due to aerodynamic loads. The effect of the pressure distributions, calculated by way of the XFOIL software, and of the actuators loads, is estimated by FE analyses of the loaded wing. Two prototypes are then realised incorporating the variable airfoil and the hingeless aileron features respectively, and the verification of their shapes in both the actuated and non-actuated states, supported by image analysis techniques, confirms that interesting results are achievable with the proposed lay out and design considerations.

• Steel and Composite Structures
• /
• 제3권6호
• /
• pp.403-420
• /
• 2003

In the paper one investigates the benefits deriving from the introduction of SMA provisions in a structure subject to dynamic excitation and vertical loads. At this purpose one considers a multi-degree-of-freedom (mdof) shear elastic-plastic frame and designs couples of super-elastic SMA tendons to be placed at critical locations of the structure. Particular attention is focused on the reduction of $P-{\Delta}$ effects.

• 소성∙가공
• /
• 제22권4호
• /
• pp.216-222
• /
• 2013

Solid polymers exhibit rate-dependent deformation behavior such as nonlinear strain rate sensitivity and stress relaxation like metallic materials. Despite the different microstructures of polymeric and metallic materials, they have common properties with respect to inelastic deformation. Unlike most metallic materials, solid polymers and shape memory alloys (SMAs) exhibit highly nonlinear stress-strain behavior upon unloading. The present work employs the viscoplasticity theory [K. Ho, 2011, Trans. Mater. Process. 20, 350-356] developed for the pseudoelastic behavior of SMAs, which is based on unified state variable theory for the rate-dependent inelastic deformation behavior of typical metallic materials, to depict the curved unloading behavior of polyphenylene oxide (PPO). The constitutive equations are characterized by the evolution laws of two state variables that are related to the elastic modulus and the back stress. The simulation results are compared with the experimental data obtained by Krempl and Khan [2003, Int. J. Plasticity 19, 1069-1095].

• 한국지능시스템학회논문지
• /
• 제26권2호
• /
• pp.147-152
• /
• 2016

형상기억합금은 가열되거나 냉각될 때 모양과 강도가 변화하면서 큰 힘을 발생한다. 와이어 형태의 형상기억합금은 열을 가하면 길이가 축소되면서 상당히 큰 힘을 발휘하며, 소음없는 운동을 발생시킬 수 있으므로 모터를 대체할 수 있는 구동기로 활용가능하다. 이런 형상기억합금 구동기는 전기로 직접 가열할 수 있으며, 큰 범위의 운동을 만들어내는데 사용될 수 있다. 본 논문에서는 형상기억합금 구동기를 이용하여 3 개의 손가락을 가진 6 자유도의 로봇 손을 개발하고 제어하는 것에 대해 기술한다. 각 손가락은 2 개의 관절을 가지고 있으며, 각 관절은 길항(拮抗) 운동을 위해 서로 반대로 동작하는 두 개의 힘줄에 의해 구동된다. 부드러운 운동을 위한 충분한 힘을 만들어 내기 위해 각 힘줄은 2 개의 형상기억합금 구동기가 병렬로 구성된다. 형상기억합금 구동기를 가열하기 위한 전류를 제어하기 위해 PWM 드라이버를 채용하였으며, 실험을 통해 손가락의 길항 작용을 평가한다.

• Structural Engineering and Mechanics
• /
• 제60권3호
• /
• pp.507-527
• /
• 2016

The use of shape memory alloys (SMAs) has been seriously considered in seismic engineering due to their capabilities, such as the ability to tolerate cyclic deformations and dissipate energy. Five 3-D extended end-plate connection models have been created, including one conventional connection and four connections with Nitinol bolts of four different prestress forces. Their cyclic behaviors have been investigated using the finite element method software ANSYS. Subsequently, the moment-rotation responses of the connections have been derived by subjecting them to cyclic loading based on SAC protocol. The results obtained in this research indicate that the conventional connections show residual deformations despite their high ductility and very good energy dissipation; therefore, they cannot be repaired after loading. However, while having good energy dissipation and high ductility, the connections equipped with Nitinol bolts have good recentering capability. Moreover, a connection with the mentioned specifications has been modeled, except that only the external bolts replaced with SMA bolts and assessed for seismic loading. The suggested connection shows high ductility, medium energy dissipation and very good recentering. The main objective of this research is to concentrate the deformations caused by cyclic loading on the connection in order to form super-elastic hinge in the connection by the deformations of the shape memory alloy bolts.

• 한국강구조학회 논문집
• /
• 제27권6호
• /
• pp.493-501
• /
• 2015

초탄성 형상기억합금은 상온에서 소성 범위를 초월하여 상당량의 변위를 가하더라도 하중을 제거 후에 별도의 열처리를 가하지 않더라도 원상태로 복원이 가능한 특수한 금속이다. 자동치유가 가능한 형상기억합금의 특유한 재료적인 성질로 인하여 구조물에서 변위가 집중되는 부분에 기존에 주로 사용되는 강재를 대체하여 이러한 특수 합금 재료가 널리 활용되기 시작하였다. 하지만 형상기억합금을 활용한 구조물의 기본적인 설계와 성능 검증을 하기 위해 고등적인 구조해석에 필요한 재료적인 모델의 개발과 연구의 노력이 부족하기 때문에 본 재료를 현장에서 적용하기에는 여전히 많은 제약을 받고 있다. 따라서 본 연구에서는 초탄성 형상기억합금의 거동을 수치해석적인 방법으로 재현이 가능한 구성적인 재료 모델의 소개와 프로그램 코딩에 대하여 다루고자 한다. 또한 본 연구에서 제시된 재료 모델의 타당성을 입증하기 위하여 수치해석적으로 재현된 물리적인 거동을 실험에서 얻어진 데이터에 비교 및 보정 작업도 수행하였다. 아울러 이러한 재료 모델로 구현된 초탄성 형상기억합금의 물리적인 물성치를 구조 해석에 적용하고 정확성을 검증하여 현장 적용의 타당성을 입증하였다.