• Wind and Structures
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• 제32권1호
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• pp.31-46
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• 2021

The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micromechanical systems such as micro-sized sensors and actuators.

• Smart Structures and Systems
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• 제29권4호
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• pp.589-598
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• 2022

Timber structures are susceptible to structural damages caused by variations in moisture content (MC), inducing severe durability deterioration and safety issues. Therefore, it is of great significance to detect MC levels in timber structures. Compared to current methods for timber MC detection, which are time-consuming and require bulky equipment deployment, Lead Zirconate Titanate (PZT)-enabled stress wave sensing combined with statistic machine learning classification proposed in this paper show the advantage of the portable device and ease of operation. First, stress wave signals from different MC cases are excited and received by PZT sensors through active sensing. Subsequently, two non-baseline features are extracted from these stress wave signals. Finally, these features are fed to a statistic machine learning classifier (i.e., naïve Bayesian classification) to achieve MC detection of timber structures. Numerical simulations validate the feasibility of PZT-enabled sensing to perceive MC variations. Tests referring to five MC cases are conducted to verify the effectiveness of the proposed method. Results present high accuracy for timber MC detection, showing a great potential to conduct rapid and long-term monitoring of the MC level of timber structures in future field applications.

• The Plant Pathology Journal
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• 제39권5호
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• pp.449-465
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• 2023

Plants are challenged by various pathogens throughout their lives, such as bacteria, viruses, fungi, and insects; consequently, they have evolved several defense mechanisms. In addition, plants have developed localized and systematic immune responses due to biotic and abiotic stress exposure. Animals are known to activate DNA damage responses (DDRs) and DNA damage sensor immune signals in response to stress, and the process is well studied in animal systems. However, the links between stress perception and immune response through DDRs remain largely unknown in plants. To determine whether DDRs induce plant resistance to pathogens, Arabidopsis plants were treated with bleomycin, a DNA damage-inducing agent, and the replication levels of viral pathogens and growth of bacterial pathogens were determined. We observed that DDR-mediated resistance was specifically activated against viral pathogens, including turnip crinkle virus (TCV). DDR increased the expression level of pathogenesis-related (PR) genes and the total salicylic acid (SA) content and promoted mitogen-activated protein kinase signaling cascades, including the WRKY signaling pathway in Arabidopsis. Transcriptome analysis further revealed that defense-and SA-related genes were upregulated by DDR. The atm-2atr-2 double mutants were susceptible to TCV, indicating that the main DDR signaling pathway sensors play an important role in plant immune responses. In conclusion, DDRs activated basal immune responses to viral pathogens.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.781-784
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• 2005

Twenty four types of thermopile for micro spectrometer infrared sensors were fabricated on low-stress $Si_3N_4$ membranes with $1.2{\mu}m-thickness$ using MEMS technology. Poly-Si thin film with thickness of 3500 ${\AA}$ as the first thermocouple material, was deposited by LPCVD method. And aluminum thin film with thickness of 6000 ${\AA}$ as the second thermocouple material, was deposited by sputtering method. Thermopile were designed and fabricated for optimum conditions by five parameters of thermocouple numbers (16 ${\sim}$ 48), thermocouple line widths (10 ${\mu}m$ ${\sim}$ 25 ${\mu}m$), thermocouple lengths (100 ${\mu}m$ ${\sim}$ 500 ${\mu}m$), membrane areas ($1^2\;mm^2$ ${\sim}$ $2.5^2\;mm^2$) and junction areas (150 ${\mu}m^2$ ${\sim}$ 750 ${\mu}m^2$), respectively. Electromotive forces of fabricated thermopile were measured 1.1 mV ${\sim}$ 7.4 mV at $400^{\circ}C$. It was thought that measurement results could be used for thermopile infrared sensors optimum structure for micro spectrometers.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.361.1-361.1
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• 2016

Due to their high sensitivity, fast response, small energy consumption and ease of integration, nanoelectromechanical systems (NEMS) have attracted much interest in various applications such as high speed memory devices, energy harvesting devices, frequency tunable RF receivers, and ultra sensitive mass sensors. Since the device performance of NEMS is closely related with the mechanical and flexural properties of the material in NEMS, analysis of the mechanical and flexural properties such as intrinsic tensile stress and Young's modulus is a crucial factor for designing the NEMS structures. In the present work, the intrinsic mechanical properties of highly stressed silicon nitride (SiN) beams are investigated as a function of the beam length using two different techniques: (i) dynamic flexural measurement using optical interferometry and (ii) quasi-static flexural measurement using atomic force microscopy. The reliability of the results is analysed by comparing the results from the two different measurement techniques. In addition, the mass density, Young's modulus and internal stress of the SiN beams are estimated by combining the techniques, and the prospect of SiN based NEMS for application in high sensitive mass sensors is discussed.

• Smart Structures and Systems
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• 제20권2호
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• pp.175-180
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• 2017

The load-carrying capacity and structural behavior of concrete-filled steel tube (CFST) structures is highly influenced by the grouting compactness in the steel tube. Due to the invisibility of the grout in the steel tube, monitoring of the grouting progress in such a structure is still a challenge. This paper develops an active sensing approach with combined piezoceramic-based smart aggregates (SA) and piezoceramic patches to monitor the grouting compactness of CFST bridge structure. A small-scale steel specimen was designed and fabricated to simulate CFST bridge structure in this research. Before casting, four SAs and two piezoceramic patches were installed in the pre-determined locations of the specimen. In the active sensing approach, selected SAs were utilized as actuators to generate designed stress waves, which were detected by other SAs or piezoceramic patch sensors. Since concrete functions as a wave conduit, the stress wave response can be only detected when the wave path between the actuator and the sensor is filled with concrete. For the sake of monitoring the grouting progress, the steel tube specimen was grouted in four stages, and each stage held three days for cement drying. Experimental results show that the received sensor signals in time domain clearly indicate the change of the signal amplitude before and after the wave path is filled with concrete. Further, a wavelet packet-based energy index matrix (WPEIM) was developed to compute signal energy of the received signals. The computed signal energies of the sensors shown in the WPEIM demonstrate the feasibility of the proposed method in the monitoring of the grouting progress.

• 한국자기학회지
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• 제25권4호
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• pp.123-128
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• 2015

철은 강도와 경도가 높고 전기전도도가 훌륭한 원소이며, 또한 가공이 쉽기 때문에 다양한 분야에서 사용되고 있다. 교량에서는 큰 하중이면서도 경량화를 위하여 강철선으로 된 텐던이 사용되고 있다. 철이 구조용 강으로 사용될 경우 중요한 문제 중 하나인 안전 진단을 위해서는 비파괴 검사(Non-Destructive Testing)가 필수적인데 철강의 자기적 특성이 비선형의 자화곡선과 이력(hysteresis)현상이 있는 자기이력곡선으로 인하여 비파괴 검사에 적용이 어렵다. 본 연구에서는 교량에 부착되어 있는 텐던의 인장변형력을 비파괴 적이면서 자기적인 방법으로 측정하기 위한 기초 연구로, 텐던의 인장변형력에 의한 자기이력 특성변화를 관찰하기 위하여 직경 15.5 mm의 7-strand 텐던에 인장력을 0에서 2 GPa까지 인가할 수 있는 자기이력곡선 측정 장치를 제작하였다. 제작 된 자기이력곡선 측정 장치를 이용하여 시판되고 있는 두 제조회사의 텐던에 대하여 자기적 특성을 조사하였고, 인장변형력에 따른 자기적 특성의 변화가 가장 큰 부분은 자기이력곡선 상의 knee 부분 근처에서의 상대 진폭투자율로 500에서 200까지 감소하였으며 최대 자속밀도 또한 0.6 T 정도로 변화하였다. 텐던의 인장변형력을 측정하는 방법으로 knee 부분의 진폭투자율 측정뿐만 아니라 최대 자속밀도의 측정방법도 가능할 것으로 생각된다.

• 한국터널지하공간학회 논문집
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• 제25권6호
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• pp.509-523
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• 2023

고준위방사성폐기물 처분장은 고온, 다습, 방사선의 복합적인 환경 조건에 노출되며 이로 인해 구조물의 열화가 가속된다. 따라서 처분장에 대한 구조물 건전성 모니터링이 필수적이며 균열 탐지, 강도 추정 등을 위해 피에조 센서가 활용된다. 다만 처분 터널 및 처분 용기에 설치되는 모니터링 센서는 교체 및 제거가 불가능하기 때문에 모니터링 센서의 정량적인 수명을 평가하고 적합성을 판단해야 한다. 본 연구에서는 가속수명시험을 활용하여 모니터링용 피에조 센서에 대한 수명을 평가하였다. 고온 조건에서 나타나는 피에조 센서의 고장 모드와 고장 메커니즘을 도출하였으며 온도 스트레스가 피에조 센서 수명에 미치는 영향을 분석하였다. 또한 온도 스트레스에 대한 가속수명시험을 수행하여 와이블 수명 확률 분포 및 아레니우스 가속모형을 통해 온도 스트레스와 피에조 센서 수명 간의 관계식을 제시하고 수명을 평가하였다. 본 연구에서 제시된 온도 스트레스와 수명 간의 관계를 통해 보다 정확한 수명 평가를 위한 복합스트레스 가속수명시험 설계에 도움이 될 것으로 판단된다.

• Design & Manufacturing
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• 제11권2호
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• pp.51-56
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• 2017

Nitinol, a shape memory alloy (SMA), is manufactured from titanium and nickel and it used in various fields such as electrical applications, micro sensors. It is also recommended as a material in medical for implant because it has excellent organic compatibility. Nitinol is intended to be inserted into the human body, products require a high-quality surface and low residual stress. To overcome this problems, explore electrolyte polishing (EP) is being explored that may be appropriate for use with nitinol. EP is a particularly useful machining method because, as a non contact machining method, it produces neither machining heat nor internal stress in the machined materials. Sandpaper polishing is also useful machining method because, as a contact machining method, it can easily good surface roughness in the machined materials. The electrolyte polishing (EP) process has an effect of improving the surface roughness as well as the film polishing process, but has a characteristic that the residual stress is hardly generated because the work hardened layer is not formed on the processed surface. The sandpaper polishing process has the effect of improving the surface roughness but the residual stress remains in the surface. We experimented with three conditions of polishing process. First condition is the conventional polishing. Second condition is the electrochemical polishing(EP). And Last condition is a mixing process with the conventional polishing and the EP. Surface roughness and residual stress of the nitinol before a polishing process were $0.474{\mu}mRa$, -45.38MPa. Surface roughness and residual stress of the nitinol after mixing process of the conventional polishing and the EP were $1.071{\mu}mRa$, -143.157MPa. Surface roughness and residual stress of the nitinol after conventional polishing were $0.385{\mu}mRa$ and -205.15MPa. Surface roughness and residual stress of sandpaper and EP nitinol were $1.071{\mu}mRa$, -143.157MPa. The result shows that the EP process is a residual stress free process that eliminates the residual stress on the surface while eliminating the deformed layer remaining on the surface through composite surface machining rather than single surface machining. The EP process can be used for biomaterials such as nitinol and be applied to polishing of wafers and various fields.

• 해양환경안전학회지
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• 제17권3호
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• pp.269-274
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• 2011

주5일제 정착, 소득의 향상, 연안지역 접근성 개선으로 해양관광 활동에 대한 관심과 해양레저 활동에 대한 수요가 증가하고 있으나, 해양활동을 위한 인프라구축 및 레저선박과 인명의 안전을 위한 시스템개발은 미비한 실정이다. 일반선박과 달리 레저선박은 구조안전성 평가 시스템을 위한 규정 및 적용 기준이 명확히 정립되어 있지 않으며, 시스템 개발이 전무하여 레저보트의 운항안전성 확보를 위한 레저보트 구조 안전모니터링시스템의 개발이 필요하다. 따라서 본 연구에서는 도파로 어레이 격자(AWG, Arrayed waveguide grating)와 광섬유 브래그 격자 센서(FBG)를 이용하여 레저보트의 실시간 선체구조모니터링이 가능한 시스템을 개발하여 해상에서의 인명과 레저선박의 안전성을 확보하고자 한다.