• Computers and Concrete
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• 제34권1호
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• pp.123-135
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• 2024

Strain-hardening cement-based composites (SHCC) under cracked condition exhibits remarkable capillary absorption due to water ingress from multiple cracks. Surface treatment using water repellent agents is an effective way for improving water resistance of SHCC, but the water resistance may remarkably decrease when cracks penetrate impregnation depth. Another way is to add water repellent agents directly into the mixture, offering SHCC integral water repellency even if cracks form later. However, although integral water repellent treatment has been proved feasible by previous studies, there is still lack of simulation work on the treated SHCC for evaluating its durability. This study presents a simulation method for capillary absorption of cracked SHCC with integral treatment based on a multi-scale approach proposed in the authors' previous work. The approach deals with water flows in bulk matrix and multiple cracks using two individual transport equations, respectively, whereas water absorbed from a crack to its adjacent matrix is treated as the mass exchange of the two equations. In this study, the approach is enhanced for the treated SHCC by integrating the influencing of water repellency into the two transport equations as well as the mass exchange term. Using the enhanced approach, capillary absorption of water repellent SHCC under cracked condition is simulated, showing much more reduced water ingress than the untreated concrete, which is consistent with total absorption data from previous tests. This approach is also capable of simulating water spatial distribution with time in treated SHCC reasonably.

• Structural Engineering and Mechanics
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• 제72권1호
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• pp.19-30
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• 2019

The mechanical behavior of Fiber Reinforced Cementitious Composites (FRCC) under direct shear is studied through experiment and analytical simulation. The cementitious composite considered contains 55% replacement of cement with fly ash and 2% (volume ratio) of short discontinuous synthetic fibers (in the form of mass reinforcement, comprising PVA - Polyvinyl Alcohol fibers). This class of cementitious materials exhibits ductility under tension with the formation of multiple fine cracks and significant delay of crack stabilization (i.e., localization of cracking at a single location). One of the behavioral parameters that concern structural design is the shear strength of this new type of fiber reinforced composites. This aspect was studied in the present work with the use of Push-off tests. The shear strength is then compared to the materials' tensile and splitting strength values.

• 한국정밀공학회지
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• 제32권6호
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• pp.529-536
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• 2015

A defect could be generated in bolts for a use of oil filters for the manufacturing process and then may affect to the safety and quality in bolts. Also, fine defects may be imbedded in oil filter system. So it is very important that such defects be investigated and screened during the multiple manufacturing processes. Therefore, in order effectively to evaluate the fine defects, the FEM simulations were performed to make characterization in the crack detection of the bolts and the parameters such as number of turns of the coil, the coil size, applied frequency were calculated based on the simulation results. Simulations were carried out for the defect signal of eddy current probe. Exciter and receiver were utilized. In this paper, the FEM simulations were performed in both bobbin-type and pancake-type probe, both probes were optimized under Eddy current FEM simulations and the results of calculation were discussed.

• 비파괴검사학회지
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• 제32권2호
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• pp.162-169
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• 2012

본 논문은 초음파 적외선 열화상과 위상잠금 방법을 이용하여 이종금속용접(STS304 and SA106 Gr. b)된 파이프의 응력부식균열 결함을 검출하였다. 초음파 가진장치는 출력 250 Watt, 주파수 20 kHz이었다. 실험 결과 이종금속용접부의 파이프 내부에 위치한 균열을 적외선 열화상을 이용하여 검출할 수 있었다. 실제 PT검사를 통하여 배관 내부의 균열이 하나가 아닌 일정한 범위 안에 하나 이상의 크랙이 존재하여 열화상 이미지 상에 넓은 범위의 hot spot 이미지를 만들어 냈음을 파악할 수 있었다. 또한 기존 기술로 검출이 용이하지 못한 마이크로 폭의 미세균열을 검출할 수 있었다. 또한, 초음파탐상기술은 $10\;{\mu}m$ 미세크랙의 폭을 갖은 균열을 쉽게 검출하지 못하였다. 그러나 초음파 적외선 열화상 기술은 결함 검출하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제21권6호
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• pp.178-184
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• 2017

이 연구에서는 PE 섬유를 사용한 고연성 시멘트 복합체에 대해 최대입경 4.75 mm의 일반모래(강모래)를 규사와 서로 다른 비율로 혼합하여 사용하였을 때, 그에 따른 고연성 시멘트 복합체의 인장거동 변화를 실험을 통해 살펴보고자 하였다. 유동성 평가 실험에서는 강모래 치환율이 증가함에 따라 유동성이 증가하는 것으로 나타났다. 압축강도는 평균압축강도에는 큰 차이가 없었으나, 편차의 크기가 강모래 치환율이 증가할수록 증가하는 것으로 나타났다. 일축인장시험 결과에서는 강모래 치환율에 따른 인장강도의 변화는 거의 없는 것으로 나타났으며, 인장변형률 성능에서는 강모래 치환율이 증가함에 따라 향상되는 결과를 나타내었다. 강모래 치환율이 증가함에 따라 다중균열의 분포밀도가 증가하면서 인장변형률 성능의 향상된 것으로 보인다. 한편, 인장변형률 성능의 편차는 압축강도에서와 마찬가지로 강모래 치환율이 증가함에 따라 커지는 양상을 나타내었다. 이 연구를 통해 규사 대신 일반모래를 사용한 경우에도 고연성 시멘트 복합체의 인장거동의 변동성은 증가하지만, 규사를 사용한 고연성 시멘트 복합체와 비교할 때 등가 이상의 인장성능을 나타낼 수 있음을 확인하였다.

• Smart Structures and Systems
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• 제6권3호
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• pp.197-209
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• 2010

The structural state of a bridge is currently examined by visual inspection or by wired sensor techniques, which are relatively expensive, vulnerable to inclement conditions, and time consuming to undertake. In contrast, wireless sensor networks are easy to deploy and flexible in application so that the network can adjust to the individual structure. Different sensing techniques have been used with such networks, but the acoustic emission technique has rarely been utilized. With the use of acoustic emission (AE) techniques it is possible to detect internal structural damage, from cracks propagating during the routine use of a structure, e.g. breakage of prestressing wires. To date, AE data analysis techniques are not appropriate for the requirements of a wireless network due to the very exact time synchronization needed between multiple sensors, and power consumption issues. To unleash the power of the acoustic emission technique on large, extended structures, recording and local analysis techniques need better algorithms to handle and reduce the immense amount of data generated. Preliminary results from utilizing a new concept called Acoustic Emission Array Processing to locally reduce data to information are presented. Results show that the azimuthal location of a seismic source can be successfully identified, using an array of six to eight poor-quality AE sensors arranged in a circular array approximately 200 mm in diameter. AE beamforming only requires very fine time synchronization of the sensors within a single array, relative timing between sensors of $1{\mu}s$ can easily be performed by a single Mote servicing the array. The method concentrates the essence of six to eight extended waveforms into a single value to be sent through the wireless network, resulting in power savings by avoiding extended radio transmission.

• 한국구조물진단유지관리공학회 논문집
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• 제23권2호
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• pp.92-98
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• 2019

일반적인 고인성 고성능 시멘트 복합재료의 경우 균질한 재료분포를 위하여 기본적으로 굵은 골재를 배재하는 경향이 있다. 그러나, 굵은 골재를 배재한 섬유 복합 시멘트 모르타르의 경우 재료의 탄성계수가 낮으며 단위시멘트량이 높아 경제성과 효율이 낮은 배합이기 때문에 대량으로 신규 구조물에 적용하기 힘들다. 따라서, 본 연구에서는 적절한 수준의 굵은 골재를 혼입하였지만 여전히 휨인성과 휨강도는 확보하고 있는 동시에, 균열 분산성능도 보유하고 있는 고인성 섬유보강 콘크리트에 대한 개발 연구를 수행하였다. 굵은 골재의 혼입량을 실험 변수로 실험 연구를 수행하였고, 결과에 따르면 고인성 모르타르의 기본 배합에 굵은골재를 잔골재의 25%중량비로 추가한 경우에서 가장 좋은 휨인성 그리고 균열분산 특성을 나타내었다. PVA섬유는 균열분산과 연성 증진에 효과적이었고, 강섬유 섬유의 경우 균열분산보다는 강도증진에 효과적이었다.