• Steel and Composite Structures
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• 제20권5호
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• pp.983-997
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• 2016

The aim of this study is to investigate the impact behavior and impact-induced damage of sandwich composites made of E-glass/epoxy face sheets and PVC foam. The studies were carried out on square flat and curved sandwich panels with two different radius of curvatures. Impact tests were performed under impact energies of 10 J, 25 J and 80 J using an instrumented drop-weight machine. Contact force and displacement versus time and contact force- displacement graphs of sandwich panels were presented to determine the panel response. Through these graphs, the energy absorbing capacity of the sandwich panels was determined. The impact responses and failure modes of flat and curved sandwich panels were compared and the effect of curvature on sandwich composite panel was demonstrated. Testing has shown that the maximum contact force decrease while displacement increases with increasing of panel curvature and curved panels exhibits mixed failure mode, with cylindrical and cone cracking.

• Geomechanics and Engineering
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• 제21권3호
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• pp.289-300
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• 2020

Estimating the damage induced by an explosion around a blast hole has always been a challenging issue in geotechnical engineering. It is difficult to determine an exact dimension for damage zone since many parameters are involved in the formation of failures, and there are some uncertainties lying in these parameters. Thus, the present study adopted a probabilistic approach towards this problem. First, a reliability model of the problem was established and the failure probability of induced damage was calculated. Then, the corresponding exceedance risk curve was developed indicating the relation between the failure probability and the cracked zone radius. The obtained risk curve indicated that the failure probability drops dramatically by increasing the cracked zone radius so that the probability of exceedance for any crack length greater than 4.5 m is less than 5%. Moreover, the effect of each parameter involved in the probability of failure, including blast hole radius, explosive density, detonation velocity, and tensile strength of the rock, was evaluated by using a sensitivity analysis. Finally, the impact of the decoupling ratio on the reduction of failures was investigated and the location of its maximum influence was demonstrated around the blast point.

• 항공우주시스템공학회지
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• 제8권3호
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• pp.41-46
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• 2014

Fatigue evaluations for the rotor blades of commercial or military rotorcraft have been carried out using the safe life concept since 1950s. Particularly, in the case of a rotor blade made of a composite material, a highly reliable fatigue life could be predicted by evaluation the cumulative damage using combination of fatigue life curve and load spectrum. However, there is a limit in adequately evaluating the strength reducing phenomena caused by damages or defects generated during the manufacturing process or impact damage induced by operational usages, using only the safe life concept. In this study, the fatigue evaluation process based on the damage tolerance concept is described and illustrated by means of successful application to substantiate the retirement time of composite rotor blades.

• 대한의용생체공학회:의공학회지
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• 제17권2호
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• pp.215-220
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• 1996

Impact force and strains induced by impact between the occluder and the struts have been measured with force sensor and strain gages. The maximum reaction force was about 25N, and the calculated impact force on the root of the struts amount about 9-17W. Impact force on the inlet strut is greater than that of the outlet strut, but the strain on the outlet strut is much higher than that of the inlet strut. These values might cause severe damage on the valve in the critical cases. The results of this study may be extended for the analysis of the endurance limit and optimal design of the struts and occluder.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 춘계학술대회
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• pp.167-171
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• 1996

Impact force and strains induced by impact between the occluder and the struts have been measured with force senfor and strain gages. The maximum reaction force was about 25N, and the calculated impact force on the root of the struts amount about $9{\sim}17N$. Impact force on the inlet strut is greater than that of the outlet strut, but the strain on the outlet strut is much higher than that of the inlet strut. These values might cause severe damage on the valve in the critical cases. The results of this study may be extended for the analysis of the endurance limit and optimal design of the struts and occluder.

• 복합신소재구조학회 논문집
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• 제1권3호
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• pp.41-48
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• 2010

본 논문에서는 폭발하중으로 발생하는 폭풍파의 충격하중과 폭풍파로 초래된 파편의 충돌하중을 동시에 받는 철근 콘크리트 벽체 구조물의 비선형 충돌 손상거동 해석이 수행된다. 이를 위해 먼저 가상 폭발사고 시나리오로부터 철근 콘크리트 구조물에 충격과 충돌 하중이 복합적으로 작용하는 경우를 선정한다. 폭발하중으로 인한 구조물의 저항성능을 확보하기 방안으로는 복합신소재를 보강하는 경우가 고려되고, 복합신소재를 보강하지 않은 철근 콘크리트 벽체 구조물과 보강성능을 비교하여 제시한다. 또한, 막대한 시설과 비용 투자가 요구되는 폭발실험과 근접한 해석을 도출하기 위하여 실제 충격과 충돌 현상을 정확하게 묘사한 구성방정식과 상태방정식을 포함시킨 정교한 해석을 수행한다. 폭발하중과 같은 순간적인 동적 문제를 해석하기 위하여 외연적 고속충돌 해석 프로그램인 AUTODYN-3D을 활용하여 두 가지 대상구조물에 대한 수치 모의실험을 수행하고 복합신소재로 보강된 철근 콘크리트 벽체 구조물의 보강성능을 입증한다.

• 한국구조물진단유지관리공학회 논문집
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• 제28권3호
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• pp.37-46
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• 2024

본 연구에서는 충격반향법(IE)을 활용하여 철근 부식 진전에 따른 콘크리트 손상 상태를 모니터링하였다. 길이 1500 mm, 폭 400 mm, 두께 200 mm를 갖는 세 개의 철근 콘크리트 시험체를 제작하였다. 각 시험체는 보통 포틀랜드 시멘트, 고로 슬래그 미분말, 플라이 애쉬를 혼합한 세 가지 콘크리트 배합을 활용하여 제작하여, 결합재 특성에 따른 손상특성을 관찰하였다. 콘크리트 내 철근 부식은 3% NaCl 용액에서 35일 주기의 습윤 및 건조 포화 과정을 거친 후 0.5 A 전류를 인가하여 가속화되었다. 전류인가 전 습윤-건조반복(철근부식 환경조성 또는 잠재기)단계에서 수집된 초기 IE 데이터는 건조상태가 IE 신호에 미치는 영향이 크기 않음을 보여주었다. 전류를 인가한 후에는 인가 시간 증가에 따라 IE 탁월주파수와 콘크리트 P파속도의 점진적인 감소 특성을 관찰할 수 있었다. 이러한 실험결과는 IE 데이터 모니터링으로 철근 부식으로 인한 콘크리트의 점진적 손상의 주요 특성(내부 손상 개시 및 전파 속도 등)을 포착할 수 있음을 보여준다. 따라서, 철근 부식에 따른 콘크리트의 점진적 손상의 평가 및 예측에 IE 모니터링이 효과적으로 활용될 수 있을 것으로 기대한다.

• 대기
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• 제34권2호
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• pp.107-121
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• 2024

In this study, we empirically analyzed the impact of physical risks due to climate change on the soundness and operational performance of the financial industry by combining economics and climatology. Particularly, unlike previous studies, we employed the Seasonal-Trend decomposition using LOESS (STL) method to extract trends of climate-related risk variables and economic-financial variables, conducting a two-stage empirical analysis. In the first stage estimation, we found that the delinquency rate and the Bank for International Settlement (BIS) ratio of commercial banks have significant negative effects on the damage caused by natural disasters, frequency of heavy rainfall, average temperature, and number of typhoons. On the other hand, for insurance companies, the damage from natural disasters, frequency of heavy rainfall, frequency of heavy snowfall, and annual average temperature have significant negative effects on return on assets (ROA) and the risk-based capital ratio (RBC). In the second stage estimation, based on the first stage results, we predicted the soundness and operational performance indicators of commercial banks and insurance companies until 2035. According to the forecast results, the delinquency rate of commercial banks is expected to increase steadily until 2035 under assumption that recent years' trend continues until 2035. It indicates that banks' managerial risk can be seriously worsened from climate change. Also the BIS ratio is expected to decrease which also indicates weakening safety buffer against climate risks over time. Additionally, the ROA of insurance companies is expected to decrease, followed by an increase in the RBC, and then a subsequent decrease.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3748-3758
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• 1996

This study is to investigate experimentally relationships between the impact energy and moisture absorption characteristies vs.the residual bending strength with the variation of stacking seqences. When Carbon-fiber reinforced plastics(CFRP) impact-induced laminates are subjected to the high temperatures and hygrothermal effects, it is found that what CFRP laminates are impacted by a steel ball (5 mm in diametar) ; thus, the generated delamination is observed by the ultrasonic microscope. And the residual bending strength is evaluated by a three-point bending test. Also, a thermostat is used in test with the unimpacted and impacted specimens for the moisture experimentaiton. The percision electro lever scles is used to measure the moisture content(1/10, 000g).

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1213-1218
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• 2004

The present article reports extensive numerical results on the non-local characteristics of ultra-short pulsed laser-induced breakdowns of fused silica ($SiO_{2}$) by using the multivariate Fokker-Planck equation. The nonlocal type of multivariate Fokker-Planck equation is modeled on the basis of the Boltzmann transport formalism to describe the ultra-short pulsed laser-induced damage phenomena in the energy-position space, together with avalanche ionization, three-body recombination, and multiphoton ionization. Effects of electron avalanche, recombination, and multiphoton ionization on the electronic transport are examined. From the results, it is observed that the recombination becomes prominent and contributes to reduce substantially the rate of increase in electron number density when the electron density exceeds a certain threshold. With very intense laser irradiation, a strong absorption of laser energy takes place and an initially transparent solid is converted to a metallic state, well known as laser-induced breakdown. It is also found that full ionization is provided at intensities above threshold, all further laser energy is deposited within a thin skin depth.