• 한국안전학회지
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• 제38권2호
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• pp.36-43
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• 2023

In this study, a four-point bending test was conducted to assess and detect the damage to reinforced concrete structures using the acoustic emission (AE) technique. Based on the crack investigation results, flexural failure was classified into four stages and compared with the characteristic analysis results of AE parameters. The parametric characterization indicated that the activity of the primary AE signal was high in the early stage, and that of the second signal increased after the flexural cracks stabilized. Because the secondary AE signal included noise generated by friction, parameter-based analysis for damage assessment was performed using the primary signal; the secondary signal was used as complement. The activity analyses of the primary and secondary signals effectively classified crack propagation; however, determining the macrocracks and yielding of reinforcing bars had certain limitations. Nevertheless, applying the damage index with cumulative AE energy is a complementary technique for detecting and assessing structure damage that well detects the occurrence of macrocracks.

• 대한토목학회논문집
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• 제26권4A호
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• pp.693-700
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• 2006

정적 손상 탐지방법은 동적 방법과 비교해서 실제 적용하기에 단순하고 효과적이다. 본 논문에서는 정적데이타를 이용하는 방법으로 변위, 처짐각, 곡률을 이용한 강박스 교량의 손상 탐지 방법에 대해서 연구하였다. 변위는 유한요소 해석에서 얻고, 처짐각과 곡률은 변위로부터 중앙차분법을 이용하여 구하였다. 손상되지 않은 경우와 손상된 경우의 응답차의 절대값으로 손상의 위치를 탐지하였다. 손상은 박스의 모서리 균열을 singular 요소를 사용하여 직접 모델링하여, 실질적인 거동을 분석하였다. 해석 결과 응답차의 절대값으로 손상의 위치를 탐지하기에 매우 효과적이었다.

• 대한기계학회논문집A
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• 제41권2호
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• pp.129-136
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• 2017

본 연구의 목적은 항공기 주익 구조물에 대한 피로균열진전 해석 및 실험을 통하여 운영 기간에 따른 장기 운영 항공기의 손상허용성을 평가하는 하는 것이다. 이를 위하여 주익 구조물의 피로임계부위 2 곳을 대상으로, 선행 연구에서 개발된 알고리즘을 기반으로 산출된 피로응력 스펙트럼 및 상용 코드인 NASGRO 를 이용한 피로균열진전해석을 수행하고 그 결과를 참고문헌의 결과와 비교하여 피로응력 스펙트럼 및 균열진전해석방법의 타당성을 확인하였다. 또한 실제 주익 구조물에서 채취한 시험편 및 이와 동일 재료로 가공된 시험편을 대상으로 위의 피로응력 스펙트럼을 적용한 피로균열진전시험을 실시하고 그 결과를 이용하여 운영 기간에 따른 주익 구조물의 손상허용성을 평가하였다.

• 대한기계학회논문집
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• 제19권2호
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• pp.451-462
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• 1995

Single overload tests performed to examine the crack retardation behavior for the specimen thickness and overload ratios. Delayed crack length was tend to increase in small thickness and big overload ratio but was difference between delayed crack length and plastic zone size that expected in specimen thickness. So retardation behavior that estimated in plastic zone size, was not sufficient. Crack tip branching and striation distribution, secondary mechanisms that effected in retardation behavior, was examined by experiment and finite element analysis. Crack tip branching was affected by micro structure, and appeared the more complicatedly according to increasing damage by overload and decreasing crack driving force in base line stress level. And crack tip branching the branching angle decreased crack driving force in the crack tip. And a characteristic of the fractography on retardation zone was that striation distribution did not appear due to decreased crack driving force.

• Smart Structures and Systems
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• 제30권4호
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• pp.385-395
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• 2022

Detecting cracks on a concrete structure is crucial for structural maintenance, a crack being an indicator of possible damage. Conventional crack detection methods which include visual inspection and non-destructive equipment, are typically limited to a small region and require time-consuming processes. Recently, to reduce the human intervention in the inspections, various researchers have sought computer vision-based crack analyses: One class is filter-based methods, which effectively transforms the image to detect crack edges. The other class is using deep-learning algorithms. For example, convolutional neural networks have shown high precision in identifying cracks in an image. However, when the objective is to classify not only the existence of crack but also the types of cracks, only a few studies have been reported, limiting their practical use. Thus, the presented study develops an image processing procedure that detects cracks and classifies crack types; whether the image contains a crazing-type, single crack, or multiple cracks. The properties and steps in the algorithm have been developed using field-obtained images. Subsequently, the algorithm is validated from additional 227 images obtained from an open database. For test datasets, the proposed algorithm showed accuracy of 92.8% in average. In summary, the developed algorithm can precisely classify crazing-type images, while some single crack images may misclassify into multiple cracks, yielding conservative results. As a result, the successful results of the presented study show potentials of using vision-based technologies for providing crack information with reduced human intervention.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.35-40
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• 2003

본 연구에서는 취성재료이면서, 세라믹과 유사한 성질을 가지며 내부균열관찰이 용이한 상업용 유리의 표면에 세라믹 플라즈마 용사 코팅한 후 입자 충격시험을 실시하였다. 코팅분말로는 매마모성 및 내충격성이 우수하여 산업계에서 널리 사용되고 있는 $Al_{2}O_{3}$ 분말을 사용하였으며, 충격입자로는 고경도의 STB2 볼베어링강을 사용하였다. 공기압축기를 장착한 입자 충격시험기를 이용하여 강구입자 충격시험을 실시한후, 실체현미경을 이용하여 손상정도를 분석하였다. 그리고 코팅입자의 크기 및 기공율에 따른 손상 정도를 분석 방법에 따라 손상정도를 비교${\cdot}$검토하였다.

• 한국기계가공학회지
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• 제6권3호
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• pp.92-97
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• 2007

The overlay welding the automobile where the durability is demanded, it is used in the vessel engine valve, plant valve and pump parts. Cause of damage public opinion one what is thought is the fatigue load due to the opening and shutting operation right time repetition of the engine valve. The damage cause of the engine valve or explanation of destruction mechanism is very difficult. The research which it sees to make clear a overlay welding of Co-alloy by Plasma Transferred Arc Weld Surfacing Process reconsideration fatigue crack initiation and fatigue crack growth mechanism at high temperature.

• 대한기계학회논문집A
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• 제27권6호
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• pp.981-986
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• 2003

In order to investigate the possibility of processing of brittle material by ball impact, the effects of boundary conditions about impact damage of soda-lime glass by small spheres were evaluated experimentally. It was investigated that crack appearance developed in soda-lime glass with boundary conditions of without sealing, single-sealing and double-sealing by impact velocity. The double-sealing was most effective in the development of perfect cone than other boundary condition. In case of double-sealing condition, PVC and Polyurethane sealing were more effective in producing a perfect cone formation than other sealing materials. The impact velocity range over which perfect cones were formed was influenced by both the contact area and diameter of impact particle.

• Computers and Concrete
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• 제20권6호
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• pp.689-704
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• 2017

The paper presents experimental and numerical investigations of prefabricated composite structural building reinforced concrete slabs with the insulating material for a residential building construction. The building slabs were composed of concrete and expanded polystyrene. In experiments, the slabs in the full-scale 1:1 were subjected to vertical concentrated loads and failed along a diagonal shear crack. The experiments were numerically evaluated using the finite element method based on two different constitutive continuum models for concrete. First, an elasto-plastic model with the Drucker-Prager criterion defined in compression and with the Rankine criterion defined in tension was used. Second, a coupled elasto-plastic-damage formulation based on the strain equivalence hypothesis was used. In order to describe strain localization in concrete, both models were enhanced in the softening regime by a characteristic length of micro-structure by means of a non-local theory. Attention was paid to the formation of critical diagonal shear crack which was a failure precursor.

• 마이크로전자및패키징학회지
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• 제17권3호
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• pp.33-41
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• 2010

Crack propagation mechanisms of Sn-3.0Ag-0.5Cu solder were studied in strain controlled push-pull creepfatigue conditions using the fast-fast (pp) and the slow-fast (cp) strain waveforms at 313 K. Transgranular cracking was found in the pp strain waveform which led to the cycle-dominant crack propagation and intergranular cracking in the cp strain waveform that led to the time-dominant crack propagation. The time-dominant crack propagation rate was faster than the cycle-dominant crack propagation rate when compared with J-integral range which resulted from the creep damage at the crack tip in the cp strain waveform. Clear recrystallization around the crack was found in the pp and the cp strain waveforms, but the recrystallized grain size in the cp strain waveform was smaller than that in the pp strain waveform. The cycle-dominant crack propagated in the normal direction to the specimen axis macroscopically, but the time-dominant crack propagated in the shear direction which was discussed in relation with shear micro cracks formed at the crack tip.