• Tunnel and Underground Space
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• v.34 no.2
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• pp.169-184
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• 2024

This study investigates acoustic emission (AE) and micro-deformation characteristics of circular openings through biaxial compression experiments. The experimental results showed a significant increase in the frequency, count, energy, and amplitude of AE signals immediately before damage occurred in the circular opening. The differences in frequency and count between before and after damage initiation were significantly pronounced, indicating suitable factors for identifying damage occurrence in circular openings. The results for digital image correlation (DIC) technique revealed that micro-deformation was concentrated around the openings, as evidenced by the spatial distribution of strain. In addition, spalling was observed at the end of the experiments. The AE and micro-deformation characteristics presented in this study are expected to serve as fundamental data for evaluating the stability of underground openings and boreholes for deep subsurface projects.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.359-366
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• 2020

In this study, a simulation-based damage estimation method for helidecks is proposed using an artificial neural network. The structural members that share a connecting node in the helideck are regarded as a damage group, and a total of 37,400 damage scenarios are numerically generated by applying randomly assigned damage to up to three damage groups. Modal analysis is then performed for all the damage scenarios, which are selectively used as either training or validation or verification sets based on the purpose of use. An artificial neural network with three hidden layers is constructed using a PyTorch program to recognize the patterns of the modal responses of the helideck model under both damaged and undamaged states, and the network is successively trained to minimize the loss function. Finally, the estimated damage rate from the proposed artificial neural network is compared to the actual assigned damage rate using 400 verification scenarios to show that the neural network is able to estimate the location and amount of structural damage precisely.

• Journal of Korean Society of Steel Construction
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• v.10 no.2 s.35
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• pp.279-290
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• 1998

An existing Damage Index Method is verified to demonstrate its feasibility for detecting structural damage in truss bridges (1) for which modal parameters are available for a few modes of vibration and (2) for which baseline modal information is not available from its as-built state. The theory of approach to detect locations of damage and to identify baseline modal model is summarized on the basis of system identification theory and modal sensitivity theory. The feasibility of the Damage Index Method is demonstrated using a numerical example of a truss bridge with 11 subsystems of 211 members and for which only two modes of vibration were recorded for post-damaged state.

• Journal of the Society of Disaster Information
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• v.11 no.3
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• pp.406-412
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• 2015

Recently, frequent earthquakes can cause serious damage to the bridge. So newly constructed bridge is considered earthquake resistant design, and for the existing old bridge evaluation of damage state is needed. In this paper, replacement of US-artificial earthquakes which are used for the construction of fragility curve for evaluating damage state to Korean artificial earthquakes to meet the Korean specifications is studied. For the generation of artificial earthquakes, the fragility curves are constructed for the PGA, for the cases of having isolated bearing and not having that.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.1
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• pp.13-20
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• 2021

In this paper, a new algorithm is proposed to estimate the damage size by combining the reflected area with the reflected position and extracting contours in proportion to the maximum value of pixels from the visible image. The cumulative summation feature vector algorithm is used to obtain the area of the reflected signal. To get the position of the reflected signal, the signal correlation algorithm is used to decompose the reflected signal from the damage. The proposed algorithm is tested and validated for composite panels. Repetitive experiments are performed and it is confirm that the proposed algorithm is reproducible. Further, it is verified that the damage size can be estimated appropriately by the proposed algorithm.

• International Journal of Highway Engineering
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• v.10 no.1
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• pp.75-85
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• 2008

Moisture damage of asphalt mixtures can occur because of a loss of bond between the asphalt binder and the fine and coarse aggregates. Therefore, moisture damage on asphalt pavements is the main cause of potholes, which is one of the main distress type of asphalt pavement. The purpose of this study is to evaluation effect moisture damage on material properties of asphalt mixtures through the laboratory performance test. The existing Modified Lottman test procedure was improved and the number of times that thermal cyclic conditioning can be added until the asphalt mixtures is damaged, was tested in order to exhibit the changes of the material properties because of moisture damage by immersion. Through the above experiments, it was found that the material properties of asphalt mixtures on room-temperature were rapidly decreased with loss of about 50% at initial stage of moisture damage caused by the amount of repeated immersion. Also, it was found that the property damage ratio using material properties of failure energy and $DCSE_f$ by test temperature $25^{\circ}C$ were showed a high relationship to moisture damage of the asphalt mixtures caused by the amount of repeated immersion.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.31 no.4
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• pp.413-422
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• 1995

Cavitation erosion-corrosion implies damage to materials due to the shock pressure or shock wave that results when bubbles form and collapse at a metal surface within a liquid. If the liquid is corrosive to the material, a condition typically encountered in industry, the component materials may suffer serious damage by a combination of mechanical and electrochemical attack. In this study, the mild steel(SS41) was tested by using the piezoelectric vibrator with 20kHz, 24$\mu$m to cavity generation apparatus. The damage behaviour of vibration cavitation erosion-corrosion and the environment characteristics were investigated in various solutions which are seawater, tap water and distilled water. The main results obtained are as follows; 1) The cavitation erosion-corrosion damage behaviour in the seawater increases to occur at the equal degree on the middle portion and the outside portion of specimen. The distilled water specimen, on other hand, occurs beginning on the outside portion across to the middle portion of specimen. 2) The cavitation erosion-corrosion damage in the tap water of low specific resistance more increases than that in the distilled water of high specific resistance at the initial testing time and more decreases than that in it by the CaCO sub(3) film with testing time. 3) Cavitation erosion-corrosion damage characteristic divides into four regions; incubation region, acceleration region, deceleration region and steady state region.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.115-123
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• 2008

The performance prediction of fiber-reinforced composites has attracted engineer's attention in many fields, and the various theoretical and numerical methods have been proposed to predict the behavior of the fiber-reinforced composites. An evolutionary damage model for progressive interfacial debonding between circular fibers and the matrix is newly incorporated into the micromechanics-based elastoplastic model proposed by Ju and Zhang (2001) in this framework. Using the proposed model, a series of numerical simulations are conducted to illustrate the elastoplastic behavior and evolutionary damage of the framework. Furthermore, the influence of the evolutionary interfacial debonding on the behavior of the composites is investigated by comparing it with the result of a stationary damage model.

• The Academic Congress of Korean Shoulder and Elbow Society
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• 1995.05a
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• pp.7-7
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• 1995

최근에 스키가 동계스포츠로 각광받으면서 스키인구가 폭발적으로 증가함에 따라 스키손상도 많이 발생하게 되어 스키손상은 스포츠외상에서 중요한 비중을 차지하게 되었다. 스키인구의 증가에 따라 스키손상에 대한 정확한 분석과 이에 대한 예방대책이 절실히 요구되며 이에 경희대학교 의과대학 정형외과학 교실에서는 1982년 12월부터 1995년 3월까지( 1986년과 1987년을 제외 ) 11년간 용평스키장내에 동계스포츠클리닉을 개설하여 상기 기간 중 내장한 총 스키인구 3,093,667명중 스키손상으로 동계스포츠클리닉에 내원한 7,172명의 환자$(0.23\%)$에 대하여 스키손상의 년도별 발생빈도, 스키손상의 특징 스키골절과 탈구의 발생빈도 및 특징 등에 대하여 11년 간의 변화추세를 분석하였다. 11년 간의 스키장의 내장객수는 1983년을 기준 (83,100)으로 하였을 때 1995년에 $977\%로 국부 큰 증가를 보였으며, 스키인구 1000명당 손상율은 1983년의 3.4에서 1995년의 1.4(평균 2.3)로 감소하는 추세를 보였다. 스키손상의 형태는 단순열상 및 타박상등을 제외하고 슬관절 인대손상이 $22.6\%로 가장 많이 발생하였으며, 조사기간동안 수치상의 의미 있는 변화는 없었다. 스키골절 및 탈구는 스키인구 1000명당 평균 0.35였으며, 1983년의 0.90으로부터 점차 감소하여 1995년에는 0.21에 이르렀다. 연령별 스키골절 및 탈구는 20세 이하에서 평균 $41.6\%로 전체적으로 성인에서 더 많이 발생하였으며, 이는 처음 3년 간 20세 이하 골절 및 탈구가 $70.5\%로 높은 발생빈도를 보였으나 1995년도의 20세 이하 골절 및 탈구가$30.3\%까지 감소하게되어 년도가 증가함에 따라 청장년 층에 비하여 소아골절 및 탈구가 전체적으로 감소하는 경향을 보였다. 스키골절의 부위별 발생빈도는 1990년 이전까지 하지골절 및 탈구가 많았으나 이후 점차 상지의 골절 탈구가 증가하였다 하지에서 가장 많은 골절은 경골 골절이었으며, 경골골절은 회전력에 의한 나선형골절이 $76.5\%로 가장 많았고 년도에 따른 변화는 보이지 않았다. 스키손상의 발생빈도는 초기에 비하여 점차 감소하는 경향을 보였으며, 손상의 특성도 부위별, 연령별로 다양한 변화를 나타내었다.

• The Journal of Engineering Geology
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• v.11 no.3
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• pp.315-325
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• 2001

A series of laboratory tests was conducted to observe damage process by stress and to understand characteristics of permeability related with rock damage. Rock specimens which were composed of the Cretaceous medium grained granites were experienced of damage stress between 65% and 95% of the compressive strength. Rock deformation by damage process was identified with the elastic wave velocity test. Relationship between rock damage and permeability change was also analyzed by water injection test in the laboratory. According to the results of the tests, damage tends to be occurred from stress level of 80% of the compressive strength and it reduces elastic wave velocity. The damaged specimens with stress more than 80% of the compressive strength showed crack density more than 0.6 and persistent length with good connectivity of cracks. They also have higher permeability than that of specimens with crack density less than 0.6. Considered with the above results, the rock specimens used in this study were fully damaged from stress level of 80% of the compressive strength. Crack initiation and propagation by damage caused good connectivity of cracks through rock specimen. These damage process, therefore, brought high permeability coefficient through water flow conduit in the rock specimen.