• Wind and Structures
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• 제20권3호
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• pp.389-404
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• 2015

In this study, residential building damage states observed from a post-tornado damage survey in Joplin after a 2011 EF 5 tornado were used to reconstruct the near-surface wind field. It was based on well-studied relationships between Degrees of Damage (DOD) of building and wind speeds in the Enhanced Fujita (EF) scale. A total of 4,166 one- or two-family residences (FR12) located in the study area were selected and their DODs were recorded. Then, the wind speeds were estimated with the EF scale. The peak wind speed profile estimated from damage of buildings was used to fit a translating analytical vortex model. Agreement between simulated peak wind speeds and observed damages confirms the feasibility of using post-tornado damage surveys for reconstructing the near-surface wind field. In addition to peak wind speeds, the model can create the time history of wind speed and direction at any given point, offering opportunity to better understand tornado parameters and wind field structures. Future work could extend the method to tornadoes of different characteristics and therefore improve model's generalizability.

• 한국국방경영분석학회지
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• 제5권1호
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• pp.37-72
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• 1979

This paper presents the FORTRAN program for expected damage by surface-to-surface weapons. One of the methods can be used to determine the effectiveness of general purpose (GP) bombs and cluster weapons against single unitary targets, linear targets, area targets, and areas of unitary target elements, The effectiveness index is in terms of fractional damage ($F_D$) or the number of volleys ($N_V$).

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.233-239
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• 1999

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Tribology and Lubricants
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• 제16권5호
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• pp.351-356
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• 2000

The feasibility of an ultrasonic technique using a pulse-echo method of normal-incident compressional waves was evaluated for its sensitivity to the worn surface and near surface damage due to wear. Worn surfaces were generated at various oscillation frequency under a given load and amplitude and these surface were in situ monitored using a ultrasonic wave detection system. Analysis of the ultrasonic waves received from the worn surface revealed a close relationship between the surface and near-surface damage and the maximum echo-amplitude of the compressional waves. The ultrasonic technique was successful in assessing the level of severity of the worn surface in real time during the wear process. It is also shown that the wear depth can be easily measured by the calculation of change of the specimen thickness based on the wave speed measured for the specimen medium.

• Tribology and Lubricants
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• 제11권5호
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• pp.114-121
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• 1995

An ultrasonic technique using normal-incident compressional waves was used to evaluate the surface and subsurface damage in ceramics produced by Hertzian indentation. Damage was produced by a blunt indenter (tungsten carbide ball) in glass-ceramic, green glass and silicon nitride. The damage was classified into two types; (1) Hertzian cone crack, in green glass and fine grain silicon nitride, and (2) distributed subsurface micro fractures, without surface damage, produced in glass ceramic. The ultrasonic technique was successful in detecting cone craks. The measurement results with the Hertzian cone cracks indicated that cracks perpendicular to the surface could be detected by the normal-incident compressional waws. Also shown is the capability of normal-incident compressional waves in detection distributed micro-sized cracks size of subsurface microfractures.

• Smart Structures and Systems
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• 제24권2호
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• pp.233-242
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• 2019

In this paper, an inverse approach based on uniform load surface (ULS) is presented for structural damage localization and quantification. The ULS is excellent approximation for deformed configuration of a structure under distributed unit force applied on all degrees of freedom. The ULS make use of natural frequencies and mode shapes of structure and in mathematical point of view is a weighted average of mode shapes. An objective function presented to damage detection is discrepancy between the ULS of monitored structure and numerical model of structure. Solving this objective function to find minimum value yields damage's parameters detection. The teaching-learning based optimization algorithm has been employed to solve inverse problem. The efficiency of present damage detection method is demonstrated through three numerical examples. By comparison between proposed objective function and another objective function which make use of natural frequencies and mode shapes, it is revealed present objective function have faster convergence and is more sensitive to damage. The method has good robustness against measurement noise and could detect damage by using the first few mode shapes. The results indicate that the proposed method is reliable technique to damage detection in structures.

• 한국생산제조학회지
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• 제21권1호
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• pp.85-89
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• 2012

Conventional grinding of BK7 glass will normally result in brittle fracture at the surface, generating severe sub-surface damage and poor surface finish. The precision grinding of BK7 glass in parallel grinding modes has been investigated. Grinding process, maximum chip thickness, ductile/brittle regime, surface roughness and sub-surface damage have been addressed. Special attention has been given to the condition for generating a ductile mode response on the ground surface. Experiments reveal that the level of surface roughness and depth of sub-surface damage vary differently for different condition. This study gives an indication of the strategy to follow to achieve high quality ground surfaces on brittle materials.

• 한국구조물진단유지관리공학회 논문집
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• 제25권3호
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• pp.100-109
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• 2021

본 연구에서는 부식에 의하여 발생하는 표면 단면손상을 고려하여 인위적인 표면 단면손상이 도입된 원형인장 부재의 인장성능 변화를 평가하였다. 인장성능 평가를 위하여 부식수준에 따른 인위적인 단면손상을 손상 폭과 높이를 변화시켜 원형강관 시험체 표면에 도입하였으며, 단면손상 수준에 따른 인장성능 변화를 평가하였다. 인장강도 실험 결과, 원형단면 강관부재의 인장강도는 강관부재의 길이 방향 손상이 아닌 부재 둘레 방향 손상의 영향을 받는 것으로 나타났으며, 부재의 파괴는 손상이 발생한 부재의 최소 단면에서 발생하는 것으로 나타났다. 표면에 불규칙한 손상이 도입된 강관 시험체의 단면조건을 명확하게 평가할 수 없으므로, 단면손상으로 인한 인장강도 변화를 정량적으로 비교하기 위하여 동일 단면 감소효과가 고려된 강관 부재에 대한 비선형 구조해석을 실시하였다. 비선형 구조해석 결과, 실제 부재 표면에 국부적 단면손상이 발생한 부재의 인장강도는 동일 단면 감소효과를 고려한 부재의 인장강도에 비하여 상대적으로 급격하게 저하하는 것으로 평가되었다. 국부부식과 같이 표면에 불규칙한 단면손상이 발생한 부재의 잔존인장성능은 인장시험과 등가손상 단면과 구조해석 결과로부터 평가된 상관계수를 이용하여 평가 및 예측될 수 있을 것이다.

• 비파괴검사학회지
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• 제29권5호
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• pp.415-420
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• 2009

이 논문은 표면파의 비선형특성을 이용하여 재료 표면의 열화손상을 평가한 사례 연구의 결과를 보고한다. 이 연구에서는 3점 굽힘 피로시험에 의해 표면에 피로열화를 가한 알루미늄 T6 시편을 대상으로 표면파의 음향 비선형 파라미터를 측정하기 위한 실험장치를 구성하였으며, 피로시험 전후에서 측정된 비선형파라미터의 크기를 비교하였다. 특히 3점 굽힘 피로시험에 의한 표면피로손상은 시편의 중앙부 표면에 집중 될 것이 예상되므로 이 주변에서의 비선형 파라미터의 변화를 세밀히 관찰하였다. 실험결과 피로손상이 거의 없는 시편의 가장자리에서는 비선형 파라미터가 피로시험 전후에서 큰 변화가 없었지만, 표면 피로열화가 집중된 중앙부에서는 뚜렷하게 증가하는 것으로 나타났다.

• 문화기술의 융합
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• 제10권3호
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• pp.845-849
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• 2024

현재 도시철도 레일의 노후화로 인한 레일표면결함이 증가하고 있으나 국가에서 제정된 궤도성능평가에 관한 세부지침에서 레일표면손상을 기술자의 육안, 간단한 측정 도구로 점검을 수행하는 실정이다. 주기적인 선로순회작업 및 육안점검을 통해 레일표면의 결함을 발견하는 것은 매우 중요하다. 그러나 점검자의 주관적 판단에 의해 레일표면의 결함의 경중을 평가하는 것은 레일 내부의 손상을 예측하기에 상당한 제약이 따른다. 본 연구에서는 레일표면손상에 따른 레일내부 균열특성에 관한 연구로서 현장측정에서는 레일표면 손상개소를 선정하여 가속구간 및 제동구간의 노후레일 시료를 채취하여 레일표면손상 상태를 평가하고자 전자주사현미경(SEM)을 이용하여 균열특성을 분석하였다. 분석결과, 주행 중인 열차로 인해 발생하는 균열 메커니즘과 레일표면방향으로 올라오는 각도로 균열이 발생하는 가속구간의 균열특성을 실험적으로 입증하였다.