• Smart Structures and Systems
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• 제19권4호
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• pp.341-350
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• 2017

Based on the super elastic properties of the shape memory alloy (SMA) and the inverse piezoelectric effect of piezoelectric (PZT) ceramics, a kind of hybrid semi-active control device was designed and made, its mechanical properties test was done under different frequency and different voltage. The local search ability of genetic algorithm is poor, which would fall into the defect of prematurity easily. A kind of adaptive immune memory cloning algorithm(AIMCA) was proposed based on the simulation of clone selection and immune memory process. It can adjust the mutation probability and clone scale adaptively through the way of introducing memory cell and antibody incentive degrees. And performance indicator based on the modal controllable degree was taken as antigen-antibody affinity function, the optimization analysis of damper layout in a space truss structure was done. The structural seismic response was analyzed by applying the neural network prediction model and T-S fuzzy logic. Results show that SMA and PZT friction composite damper has a good energy dissipation capacity and stable performance, the bigger voltage, the better energy dissipation ability. Compared with genetic algorithm, the adaptive immune memory clone algorithm overcomes the problem of prematurity effectively. Besides, it has stronger global searching ability, better population diversity and faster convergence speed, makes the damper has a better arrangement position in structural dampers optimization leading to the better damping effect.

• Smart Structures and Systems
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• 제8권2호
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• pp.173-190
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• 2011

As a practical and effective seismic resisting technology, the base isolation system has seen extensive applications in buildings and bridges. However, a few problems associated with conventional lead-rubber bearings have been identified after historical strong earthquakes, e.g., excessive permanent deformations of bearings and potential unseating of bridge decks. Recently the applications of shape memory alloys (SMA) have received growing interest in the area of seismic response mitigation. As a result, a variety of SMA-based base isolators have been developed. These novel isolators often lead to minimal permanent deformations due to the self-centering feature of SMA materials. However, a rational design approach is still missing because of the fact that conventional design method cannot be directly applied to these novel devices. In light of this limitation, a displacement-based design approach for highway bridges with SMA isolators is proposed in this paper. Nonlinear response spectra, derived from typical hysteretic models for SMA, are employed in the design procedure. SMA isolators and bridge piers are designed according to the prescribed performance objectives. A prototype reinforced concrete (RC) highway bridge is designed using the proposed design approach. Nonlinear dynamic analyses for different seismic intensity levels are carried out using a computer program called "OpenSees". The efficacy of the displacement-based design approach is validated by numerical simulations. Results indicate that a properly designed RC highway bridge with novel SMA isolators may achieve minor damage and minimal residual deformations under frequent and rare earthquakes. Nonlinear static analysis is also carried out to investigate the failure mechanism and the self-centering ability of the designed highway bridge.

• 전기화학회지
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• 제22권1호
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• pp.22-35
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• 2019

이차 전지의 개발이 전기자동차나 스마트그리드와 같은 중대형의 에너지저장장치로 응용범위가 확대됨에 따라 이차 전지의 경제성확보가 화두가 되고 있다. 나트륨이차전지는 리튬보다 훨씬 저렴한 나트륨원료를 사용하여 저가의 차세대 이차 전지로 크게 주목받고 있다. 이에 따라 이온 반경이 큰 나트륨이온의 삽입과 탈리를 원활하게 해줄 수 있는 음극 소재의 개발이 최근 몇 년간 활발히 수행되어 왔다. 나트륨이차전지용 음극은 세 가지의 반응 메커니즘 (층간 삽입반응, 금속-합금반응, 전환반응)을 기반한 소재들이 보고되었으며, 본 총설에서는 전환반응으로 구동하는 다양한 음극 소재들을 소개하며 나트륨 전지 셀 내 반응 메커니즘을 소개하고자 한다.

• Smart Structures and Systems
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• 제24권1호
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• pp.127-139
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• 2019

Residual drifts after an earthquake can incur huge repair costs and might need to replace the infrastructure because of its non-reparability. Proper functioning of bridges is also essential in the aftermath of an earthquake. In order to mitigate pounding and unseating damage of bridges subjected to earthquakes, a self-adaptive Ni-Ti shape memory alloy (SMA)-cable-based frictional sliding bearing (SMAFSB) is proposed considering self-adaptive centering, high energy dissipation, better fatigue, and corrosion resistance from SMA-cable component. The developed novel bearing is associated with the properties of modularity, replaceability, and earthquake isolation capacity, which could reduce the repair time and increase the resilience of highway bridges. To evaluate the super-elasticity of the SMA-cable, pseudo-static tests and numerical simulation on the SMA-cable specimens with a diameter of 7 mm are conducted and one dimensional (1D) constitutive hysteretic model of the SMAFSB is developed considering the effects of gap, self-centering, and high energy dissipation. Two types of the SMAFSB (i.e., movable and fixed SMAFSBs) are applied to a two-span continuous reinforced concrete (RC) bridge. The seismic vulnerabilities of the RC bridge, utilizing movable SMAFSB with the constant gap size of 60 mm and the fixed SMAFSBs with different gap sizes (e.g., 0, 30, and 60 mm), are assessed at component and system levels, respectively. It can be observed that the fixed SMAFSB with a gap of 30 mm gained the most retrofitting effect among the three cases.

• 한국분말재료학회지
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• 제28권6호
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• pp.483-490
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• 2021

A new Fe-Cr-Mo-B-C amorphous alloy is designed, which offers high mechanical strength, corrosion resistance as well as high glass-forming ability and its gas-atomized amorphous powder is deposited on an ASTM A213-T91 steel substrate using the high-velocity oxygen fuel (HVOF) process. The hybrid coating layer, consisting of nanocrystalline and amorphous phases, exhibits strong bonding features with the substrate, without revealing significant pore formation. By the coating process, it is possible to obtain a dense structure in which pores are hardly observed not only inside the coating layer but also at the interface between the coating layer and the substrate. The coating layer exhibits good adhesive strength as well as good wear resistance, making it suitable for coating layers for biomass applications.

• 한국분말재료학회지
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• 제29권3호
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• pp.240-246
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• 2022

Novel Ni- and Fe-based alloys are developed to impart improved mechanical properties and corrosion resistance. The designed alloys are manufactured as a powder and deposited on a steel substrate using a high-velocity oxygen-fuel process. The coating layer demonstrates good corrosion resistance, and the thus-formed passive film is beneficial because of the Cr contained in the alloy system. Furthermore, during low-temperature heat treatment, factors that deteriorate the properties and which may arise during high-temperature heat treatment, are avoided. For the heattreated coating layers, the hardness increases by up to 32% and the corrosion resistance improves. The influence of the heat treatment is investigated through various methods and is considered to enhance the mechanical properties and corrosion resistance of the coating layer.

• Smart Structures and Systems
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• 제31권1호
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• pp.89-100
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• 2023

This paper conducts a parametric study of a new tuned mass damper with pre-strained superelastic SMA helical springs (SMAS-TMD) on the vibration reduction effect. First, a force-displacement relation model of superelastic SMA helical spring is presented based on the multilinear constitutive model of SMA material, and the tension tests of the six SMA springs fabricated are implemented to validate the mechanical model. Then, a dynamic model of a single floor steel frame with the SMAS-TMD damper is set up to simulate the seismic responses of the frame, which are testified by the shaking table tests. The wire diameter, initial coil diameter, number of coils and pre-strain length of SMA springs are extracted to investigate their influences on the seismic response reduction of the frame. The numerical and experimental results show that, under different earthquakes, when the wire diameter, initial coil diameter and number of coils are set to the appropriate values so that the initial elastic stiffness of the SMA spring is between 0.37 and 0.58 times of classic TMD stiffness, the maximum reduction ratios of the proposed damper can reach 40% as the mass ratio is 2.34%. Meanwhile, when the pre-strain length of SMA spring is in a suitable range, the SMAS-TMD damper can also achieve very good vibration reduction performance. The vibration reduction performance of the SMAS-TMD damper is generally equal to or better than that of the classic optimal TMD, and the proposed damper effectively suppresses the detuning phenomena that often occurs in the classic TMD.

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

• Smart Structures and Systems
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• 제4권2호
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• pp.221-232
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• 2008

This paper represents the final results of a research program sponsored by the European Commission through project WIND-CHIME ($\underline{W}$ide Range Non-$\underline{IN}$trusive $\underline{D}$evices toward $\underline{C}$onservation of $\underline{HI}$storical Monuments in the $\underline{ME}$diterranean Area), in which the possibility of using advanced seismic protection technologies to preserve historical monuments in the Mediterranean area is investigated. In the current research, the dynamic characteristics of two outstanding Mamluk-Style minarets, which similar minarets were reported to experience extensive damage during Dahshur 1992 earthquake, are investigated. The first minaret is the Qusun minaret (1337 A.D, 736 Hijri Date (H.D)) located in El-Suyuti cemetery on the southern side of the Salah El-Din citadel. The minaret is currently separated from the surrounding building and is directly resting on the ground (no vaults underneath). The total height of the minaret is 40.28 meters with a base rectangular shaft of about 5.42 ${\times}$ 5.20 m. The second minaret is the southern minaret of Al-Sultaniya (1340 A.D, 739 H.D). It is located about 30.0 meters from Qusun minaret, and it is now standing alone but it seems that it used to be attached to a huge unidentified structure. The style of the minaret and its size attribute it to the first half of the fourteenth century. The minaret total height is 36.69 meters and has a 4.48 ${\times}$ 4.48 m rectangular base. Field investigations were conducted to obtain: (a) geometrical description of the minarets, (b) material properties of the minarets' stones, and (c) soil conditions at the minarets' location. Ambient vibration tests were performed to determine the modal parameters of the minarets such as natural frequencies and mode shapes. A $1/16^{th}$ scale model of Qusun minaret was constructed at Cairo University Concrete Research Laboratory and tested under free vibration with and without SMA wire dampers. The contribution of SMA wire dampers to the structural damping coefficient was evaluated under different vertical loads and vibration amplitudes. Experimental results were used along with the field investigation data to develop a realistic 3-D finite element model that can be used for seismic risk evaluation of the minarets. Examining the updated finite element models under different seismic excitations indicated the vulnerability of such structures to earthquakes with medium to high a/v ratio. The use of SMA wire dampers was found feasible for reducing the seismic risk for this type of structures.

• 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.