• 항공우주시스템공학회지
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• 제4권4호
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• pp.11-17
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• 2010

In this paper we make an flap actuator by using shape memory effects of SMA spring. We studied that the force and stroke what we need to design and the flap mechanism. The force and stroke was estimated through the analysis program which like a catia, matlab etc. We could design and make flap actuator. So The actuator which used SMA spring can apply to small aircraft.

• 한국항공우주학회지
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• 제38권2호
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• pp.129-134
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• 2010

변형률-속도에 따른 형상기억합금의 열-기계적 특성 변화를 수치적으로 살펴보았다. 변형률 효과를 고려한 형상기억합금 수학 모델을 유도하였고, 해석 알고리즘을 ABAQUS 상용 프로그램에 적용하여 형상기억합금의 열-기계적 특성을 예측하였다. 마르텐사이트 상 변화량과 온도 변화사이의 연성된 열역학적 방정식을 적용하여, 변형률-속도에 따른 형상기억합금의 거동 특성을 살펴보았다. 변형률 효과를 고려함에 따라 형상기억합금의 의탄성 이력 특성이 크게 영향을 받음을 수치해석 결과를 통하여 알 수 있었다.

• 소성∙가공
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• 제33권5호
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• pp.330-340
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• 2024

The martensitic Ni-Ti shape memory alloys(SMA) can achieve a two-way shape memory effect (TWSME) through thermomechanical training/cycling. In this study, the surface of Ni-Ti SMA sheets was treated by depositing a certain number of titanium (Ti) powder layers using a selective laser meling (SLM) process to enhance TWSME. The results showed that a unique TWSME of approximately 12% with good stability was achieved after 100 training cycles when the optimum number of five Ti layers was deposited. A larger HAZ and lower cooling rate pushed more Ti particles into the grains rather than the grain boundaries, providing more time for Ti to react with NiTi to form Ti-rich intergranular Ti2Ni(Ox) precipitates. This resulted in further hindering of dislocation movement within the grains and the generation of internal stress fields required for attaining a larger TWSME. With an increase in the number of Ti-deposited layers, there was no noticeable reduction in the one-way shape memory effect (OWSME) through the initial cycling. This was due to the high residual tensile stress caused by the lower thermal expansion of the Ti layer compared to the Ni-Ti sheet.

• 대한토목학회논문집
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• 제33권3호
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• pp.875-888
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• 2013

최근에는 초탄성 형상기억합금을 구조물 일부에 설치하여 지진과 같은 외부 충격하중으로 인해 발생되는 영구적인 소성 변형을 줄이고 자동치유가 가능한 변위제어 시스템을 개발하는 연구가 활발하게 진행되고 있다. 초탄성 형상 기억합금은 상당량의 변위를 가하더라도 별도의 열처리 없이도 상온에서 단지 하중만을 제거하여도 원형으로 복원이 가능한 독특한 합성 금속재료이다. 뼈대 구조물에서 변형이 집중이 되는 부위에 기존에 사용된 강재를 대신하여 초탄성 형상기억합금을 사용한다면 시스템의 복원 효과를 극대화 시킬 수 있다. 따라서 본 연구는 내진성능이 우수한 좌굴방지 가새프레임에 초탄성 형상기억합금 소재를 접목시킨 새로운 구조 시스템을 제안하고 자 한다. 본 연구에서 제안된 구조시스템의 성능을 검증하기 위하여 현재 사용되는 설계코드를 참고하여 6층의 가새프레임 빌딩을 설계를 하고 2차원적인 유한요소 프레임 모델에 각각의 지진 위험도 레벨의 가속도 데이터를 사용하여 비선형 동적 해석을 실시하였다. 해석결과를 바탕으로 초탄성 형상기억합금 가새시스템을 사용한 프레임 구조물과 기존의 가새시스템을 성능적인 측면에서 서로 비교하였다. 해석결과는 지진하중 이후에 초탄성 형상기억합금 가새시스템은 구조물에 잔류 처짐을 감소하는데 매우 효율적임을 보여주고 있다.

• Advances in nano research
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• 제13권3호
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• pp.285-295
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• 2022

Creation of plastic deformation under seismic loads, is one of the most serious subjects in RC structures with steel bars which reduces the life threatening risks and increases dissipation of energy. Shape memory alloy (SMA) is one of the best choice for the relocating plastic hinges. In a challenge to study the seismic response of concrete moment resisting frame (MRF), this article investigates numerically a new type of concrete frames with nano fiber reinforced polymer (NFRP) and shape memory alloy (SMA) hinges, simultaneously. The NFRP layer is containing carbon nanofibers with agglomeration based on Mori-Tanaka model. The tangential shear deformation (TASDT) is applied for modelling of the structure and the continuity boundary conditions are used for coupling of the motion equations. In SMA connections between beam and columns, since there is phase transformation, hence, the motion equations of the structure are coupled with kinetic equations of phase transformation. The Hernandez-Lagoudas theory is applied for demonstrating of pseudoelastic characteristics of SMA. The corresponding motion equations are solved by differential cubature (DC) and Newmark methods in order to obtain the peak ground acceleration (PGA) and residual drift ratio for MRF-2%. The main impact of this paper is to present the influences of the volume percent and agglomeration of nanofibers, thickness and length of the concrete frame, SMA material and NFRP layer on the PGA and drift ratio. The numerical results revealed that the with increasing the volume percent of nanofibers, the PGA is enhanced and the residual drift ratio is reduced. It is also worth to mention that PGA of concrete frame with NFRP layer containing 2% nanofibers is approximately equal to the concrete frame with steel bars.

• Advanced Composite Materials
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• 제17권1호
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• pp.41-56
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• 2008

In this research, optical fiber sensors and shape memory alloys (SMA) were incorporated into sandwich panels for development of a smart honeycomb sandwich structure with damage detection and shape recovery functions. First, small-diameter fiber Bragg grating (FBG) sensors were embedded in the adhesive layer between a CFRP face-sheet and an aluminum honeycomb core. From the change in the reflection spectrum of the FBG sensors, the debonding between the face-sheet and the core and the deformation of the face-sheet due to impact loading could be well detected. Then, the authors developed the SMA honeycomb core and bonded CFRP face-sheets to the core. When an impact load was applied to the panel, the cell walls of the core were buckled and the face-sheet was bent. However, after the panel was heated over the reverse transformation finish temperature of the SMA, the core buckling disappeared and the deflection of the face-sheet was relieved. Hence the bending stiffness of the panel could be recovered.

• 한국생산제조학회지
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• 제25권1호
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• pp.1-6
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• 2016

Micromanufacturing is a useful system for reducing energy consumption. For micromanufacturing, tool clamping and workpiece clamping are important components to realize the machining process. Therefore, a shape memory alloy (SMA) ring type tool holder is developed. In addition, this holder needs cooling and heating processes to execute the tool clamping process. This study suggests a cooling/heating device based on peltier elements. The device will be applied to the heating/cooling process of an automatic tool changer (ATC) for the SMA tool holder. This study introduces the configuration and operating principle of the proposed ATC system. The description and prototype evaluation of this system were given. Plastic bolt and aluminum block were selected to enhance the cooling performance, and the installed tool was changed in 17 s during the experiments.

• Smart Structures and Systems
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• 제17권1호
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• pp.135-147
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• 2016

This paper describes a smart structural system, which uses smart materials for real-time monitoring and active control of bolted-joints in steel structures. The goal of this research is to reduce the possibility of failure and the cost of maintenance of steel structures such as bridges, electricity pylons, steel lattice towers and so on. The concept of the smart structural system combines impedance based health monitoring techniques with a shape memory alloy (SMA) washer to restore the tension of the loosened bolt. The impedance-based structural health monitoring (SHM) techniques were used to detect loosened bolts in bolted-joints. By comparing electrical impedance signatures measured from a potentially damage structure with baseline data obtained from the pristine structure, the bolt loosening damage could be detected. An outlier analysis, using generalized extreme value (GEV) distribution, providing optimal decision boundaries, has been carried out for more systematic damage detection. Once the loosening damage was detected in the bolted joint, the external heater, which was bonded to the SMA washer, actuated the washer. Then, the heated SMA washer expanded axially and adjusted the bolt tension to restore the lost torque. Additionally, temperature variation due to the heater was compensated by applying the effective frequency shift (EFS) algorithm to improve the performance of the diagnostic results. An experimental study was conducted by integrating the piezoelectric material based structural health monitoring and the SMA-based active control function on a bolted joint, after which the performance of the smart 'self-monitoring and self-healing bolted joint system' was demonstrated.

• Smart Structures and Systems
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• 제7권1호
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• pp.41-57
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• 2011

A deeper understanding of the effectiveness of adopting devices mounting shape memory alloy (SMA) elements in applications targeted to the mitigation of vibrations is pursued via an experimental approach. During a seismic event, less than 1000 loading-unloading cycles of the alloy are required to mitigate the earthquake effects. However, the aging effects during the time of inactivity prior to the oscillations (several decades characterized by the yearly summer-winter temperature wave) should be considered in order to avoid and/or minimize them. In this paper, the results obtained by carrying out, in different laboratories, fatigue tests on SMA specimens are compared and discussed. Furthermore, the effects of seismic events on a steel structure, with and without SMA dampers, are numerically simulated using ANSYS. Under an earthquake excitation, the SMA devices halve the oscillation amplitudes and show re-centering properties. To confirm this result, an experimental campaign is conducted by actually installing the proposed devices on a physical model of the structure and by evaluating their performance under different excitations induced by an actuator.

• Earthquakes and Structures
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• 제4권6호
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• pp.607-627
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• 2013

The application of shape memory alloys (SMAs) to the seismic response reduction of civil engineering structures has attracted growing interest due to their self-centering feature and excellent fatigue performance. The loading rate dependence of SMAs raises a concern in the seismic analysis of SMA-based devices. However, the implementation of micromechanics-based strain-rate-dependent constitutive models in structural analysis software is rather complicated and computationally demanding. This paper investigates the feasibility of replacing complex rate-dependent models with rate-independent constitutive models for superelastic SMA elements in seismic time-history analysis. Three uniaxial constitutive models for superelastic SMAs, including one rate-dependent thermomechanical model and two rate-independent phenomenological models, are considered in this comparative study. The pros and cons of the three nonlinear constitutive models are also discussed. A parametric study of single-degree-of-freedom systems with different initial periods and strength reduction factors is conducted to examine the effect of the three constitutive models on seismic simulations. Additionally, nonlinear time-history analyses of a three-story prototype steel frame building with special SMA-based damping braces are performed. Two suites of seismic records that correspond to frequent and design basis earthquakes are used as base excitations in the seismic analyses of steel-braced frames. The results of this study show that the rate-independent constitutive models, with their parameters properly tuned to dynamic test data, are able to predict the seismic responses of structures with SMA-based seismic response modification devices.