• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.657-662
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• 2007

We studied the piezoresistivity of a steel-alloy 'wire when the deformation exceeds the elastic limit. It is that the piezoresistivity of the steel-alloy wire could be modeled by a bilinear function. To predict the plastic piezoresistivity relation, we developed a simple plastic piezoresistivity model based on the classical hardening plasticity. If structural members such as prestressing tendons in concrete structures are concerned, it is a very efficient and simple tool for monitoring.

• Computers and Concrete
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• 제23권6호
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• pp.399-408
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• 2019

Structural health monitoring is important for the safety of lives and asset management. In this study, numerical models were developed for the piezoresistive behavior of smart concrete based on finite element (FE) method. Finite element models were calibrated with experimental data collected from compression test. The compression test was performed on smart concrete cube specimens with 75 mm dimensions. Smart concrete was made of cement CEM II 42.5 R, silica fume, fine and coarse crushed limestone aggregates, brass fibers and plasticizer. During the compression test, electrical resistance change and compressive strain measurements were conducted simultaneously. Smart concrete had a strong linear relationship between strain and electrical resistance change due to its piezoresistive function. The piezoresistivity of the smart concrete was modeled by FE method. Twenty-noded solid brick elements were used to model the smart concrete specimens in the finite element platform of Ansys. The numerical results were determined for strain induced resistivity change. The electrical resistivity of simulated smart concrete decreased with applied strain, as found in experimental investigation. The numerical findings are in good agreement with the experimental results.

• Composites Research
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• 제34권6호
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• pp.412-420
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• 2021

본 연구에서는 탄소 단섬유를 천연고무 기지에 혼합한 탄소섬유/고무 시편과 그에 니켈입자를 추가한 탄소섬유-니켈입자/고무 시편의 초기 전기전도도를 측정하고, 그 시편에 압축스트레인을 가하면서 변화하는 전기전도도를 측정하였다. 실험을 통해 탄소섬유의 체적분율 및 추가된 니켈입자, 외부스트레인 등이 전기전도도에 미치는 영향을 관찰하였다. 탄소섬유 체적분율은 작은 차이로도 시편의 전기전도도의 변화에 매우 큰 역할을 하였고, 외부스트레인에 따른 탄소섬유 재배열에 의해 압저항이 증가하는 것을 알 수 있었다. 또한, 니켈입자의 추가는 탄소섬유가 임계체적분율 이상인 시편에서 전기전도도를 개선하는데 기여하는 것을 볼 수 있었는데, 이로부터 외부변형에 따른 탄소섬유의 재배열에 의해 압저항이 증가하는 현상을 상쇄하는 효과가 있음을 확인하였다.

• Computers and Concrete
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• 제8권2호
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• pp.229-241
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• 2011

In this work, cement paste samples with 1% (by cement mass) of a conductive carbon fiber admixture have been studied under uniaxial compression. Three different arrangements were used to measure the resistivity of the samples. According to the results obtained, the resistance should be measured using the four wire method in order to obtain good sensitivity and repeatability. The effect of the load value and the load rate on the fractional change of the volume resistivity has been determined. It has been observed that the gage factor (fractional change in resistance respect to strain) increases when the maximum load is increased, and the loading rate does not affect significantly this parameter. The effect of the sample ambient humidity on the material piezoresistivity has also been studied, showing that the response of the composite is highly affected by this parameter.

• 한국소음진동공학회논문집
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• 제16권7호
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• pp.762-768
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• 2006

To address the need for new intelligent sensing of systems, this study presents a novel strain sensor based on piezoresistivity of carbon nanotube (CNT) and its nanocomposites. Fabrication and characterization of the carbon nanocomposite material are discussed and an electrical model of the CNT strain sensor was derived based on electrochemical impedance spectroscopy analysis and strain testing. The dynamic response of the sensor on a vibrating beam was simulated using numerical analysis and it was compared with experimental test. The simulation showed good agreement with the strain response of the actual sensor.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1999년도 춘계학술대회 논문집
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• pp.677-680
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• 1999

Rapid developing automation technology enhances the need of sensors. Among many materials, silicon has the advantages of electrical and mechanical property, Single-crystalline silicon has different piezoresistivity on 야fferent directions and a current leakage at elevated temperature, but poly-crystalline silicon has the possibility of controling resistivity using dopping ions, and operation at high temperature, which is grown on insulating layers. Each wafer has slightly different thicknesses that make difficult to obtain the precisely same thickness of a diaphragm. This paper deals with the fabrication process to make poly-crystalline silicon based pressure sensors which includes diaphragm thickness and wet-etching techniques for each layer. Diaphragms of the same thickness can be fabricated consisting of deposited layers by silicon bulk etching. HF etches silicon nitride, HNO$_3$+HF does poly -crystalline silicon at room temperature very fast. Whereas ethylenediamice based etchant is used to etch silicon at 11$0^{\circ}C$ slowly.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.350-351
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• 2006

Thick film mechanical sensors can be categorized into four main areas piezoresistive, piezoelectric, capacitive and mechanic tube. In this areas, the thick film strain gage is the earliest example of a primary sensing element based on the substrates. The latest thick film sensor is used various pastes that have been specifically developed for pressure sensor application. Some elastic materials exhibit a change in bulk resistivity when they are subjected to displacement by an applied pressure. This property is referred to as piezoresistivity and is a major factor influencing the sensitivity of a piezoresistive strain gage. The effect of thick film resistors was first noticed in the early 1970, as described by Holmes in his paper in 1973.

• 드라이브 ㆍ 컨트롤
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• 제13권1호
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• pp.43-48
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• 2016

This paper presents a preliminary study on the pressure sensing characteristics of smart nano composites made of MWCNT (multi-walled carbon nanotube) to develop a novel pressure sensor. We fabricated the composite pressure sensor by using a solution casting process. Made of carbon smart nano composites, the sensor works by means of piezoresistivity under pressure. We built a signal processing system similar to a conventional strain gage system. The sensor voltage outputs during the experiment for the pressure sensor and the resistance changes of the MWCNT as well as the epoxy based on the smart nano composite under static pressure were fairly stable and showed quite consistent responses under lab level tests. We confirmed that the response time characteristics of MWCNT nano composites with epoxy were faster than the MWCNT/EPDM sensor under static loads.

• 접착 및 계면
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• 제13권3호
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• pp.137-144
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• 2012

탄소나노소재의 화학적 기능화는 대부분 복합체 제조 시 고분자 모재(matrix)와의 계면 특성 향상을 위한 방법으로 적용되어 왔다. 계면결합력의 증가에 따른 효과는 기계적 물성의 증가를 통해 간접적으로 확인할 수 있으며, 이는 계면에서 효과적인 응력전달을 통해 설명된다. 보다 직접적으로 기능화를 통한 계면결합력 증가의 효과를 설명하기 위하여 피에조 저항효과를 관찰할 수 있으며, 이를 통하여 변형에 대한 복합체 내부의 전도성 충진재의 거동을 짐작해 볼 수 있다. 이를 위해 다중벽 탄소나노튜브(MWCNT)와 환원 그래핀(rGO)을 황산/질산 용액을 이용하여 산화반응을 통해 기능기를 도입하였으며, 기능화 전 후의 복합체의 전기적 저항 및 피에조 저항효과를 측정하였다. 결과로부터 기능기 도입으로 인해 증가한 탄소나노소재의 구조적 결함이 전기적 저항의 증가를 야기하지만 동일한 변형에 대하여 저항 변화가 더 크게 나타나 변형에 따른 복합체 내부 전도성 입자의 유동성이 증가함을 확인하였고, 이를 통해 계면결합력이 증가함을 피에조 저항효과 관찰을 통해 확인할 수 있었다.

• 한국소음진동공학회논문집
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• 제24권3호
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• pp.247-252
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• 2014

This paper presents a novel impact sensor which can be fabricated with smart paint made of grapheme. This smart nano paint can be easily installed on structures using a spray-on technique and that can make the sensor low cost and practical. The graphene effectively improves the piezoresistivity of the smart paint and that is available to achieve sensitive impact sensor with high gauge factor. The nano smart-paint can detect sufficient impact to cover the damaged energy range of the composite around 1~3J. The voltage outputs from the sprayed paints show fairly linear responses after signal processing. The impact makes deformation of the structure and it brings change of piezoresistivity of the paint and those converts into voltage output consequently by means of a simple signal processing system. The nano smart paint is lightweight and easily applied to the structural surface, and there is no stress concentration. The nano smart paint is expected to be a cost effective and sensitive multi-functional sensor for composites and other damage monitoring applications in the field of structural health monitoring.