• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.407-412
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• 2001

In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subject to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, Acoustic Emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. Cumulative AE counts were well predicted crack initiation and crack propagation and AE amplitude were useful for prediction of damage failure mode. During the matrix cracking, fiber debonding and fiber breakage, AE amplitude has $45{\sim}60dB,\;60{\sim}80dB\;and\;90{\sim}100dB$, respectively.

• Advances in concrete construction
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• 제5권5호
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• pp.539-561
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• 2017

In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium -level, high -level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.

• 전산구조공학
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• 제9권1호
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• pp.65-76
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• 1996

콘크리트의 미세공극 혹은 미세균열의 발생과 성장은 콘크리트의 점차적인 물성 저하를 야기한다. 이와같은 손상은 이방성을 가지며 소성과 함께 콘크리트의 비선형거동을 일으키는 주요원인이 된다. 본 논문은 콘크리트의 탄소성 변형 및 손상을 고려하여 콘크리트의 이방성 손상거동을 해석할 수 있는 콘크리트 연속체 손상모델의 개발에 관한 연구이다. 등가 탄성 에너지원리를 이용하여 이방 손상텐서로 표현된 유효탄성텐서를 구하고, 이를 포함하고 있는 열역학 법칙의 자유에너지함수와 소산포텐셜로부터 손상의 전개법칙을 유도한 후, 손상에너지해방률의 함수로 표현한 손상면을 적용하므로써 콘크리트의 이상성손상을 효율적으로 해석 할 수 있는 구성방정식을 유도하였다. 또한 이방성 손상모델에 콘크리트의 소성모델을 도입시켜 탄소성 변형 및 손상을 함께 고려할 수 있는 콘크리트의 연속체 손상모델을 개발하였다. 개발된 손상모델을 유한요소해석 프로그램에 적용하여 1축 및 2축의 여러 조합응력을 받는 콘크리트 모형을 유한요소해석하였으며, 실험결과 또는 타 모델과의 비교로부터 손상모델의 타당성을 검증하였다.

• Structural Engineering and Mechanics
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• 제7권2호
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• pp.225-240
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• 1999

This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.

• International Journal of Safety
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• 제4권2호
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• pp.6-11
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• 2005

The goals of the paper are to understand the impact damage behavior and identify the effect of surface protective materials on impact resistance in filament wound composite pressure vessels. For these, a series of low velocity impact tests was performed on specimens cutting from the full scale pressure vessel by the instrumented impact testing machine. The specimens are classified into two types, which are with and without surface protective material. The visualization for impact damage by two different impactors is made by metallurgical microscope. Based on the impact force history and damage, the impact resistance parameters were employed,rod its validity in identifying the damage resistance of filament wound composite pressure vessel was reviewed. As the results, the impact resistance of the filament wound composites and its dependency on the surface protective material were evaluated quantitatively

• 대한기계학회논문집A
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• 제25권7호
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• pp.1089-1096
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• 2001

This paper presents the fatigue behavior of composite materials with impact-induced damage under 2 level block loading. For this purpose, the 2 level block loading fatigue tests were performed on the impacted composite laminate. The fatigue life of the laminate under the block loading is greatly influenced by the impact damage; the effect of impact damage can be characterized by the present impact damage parameter. Based on this parameter, the model is developed to predict the fatigue life under block loading and the results by this model agree well with experimental results regardless of applied impact energy. Also, stochastic model is established to describe the variation of cumulative damage behavior and fatigue life due to the material nonhomogeneity.

• 한국구조물진단유지관리공학회 논문집
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• 제19권2호
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• pp.92-98
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• 2015

최근의 건축물은 복합적인 기능과 형태를 보이고 있으며, 크기가 거대해짐에 따라 구조물 건전성 감시 (Structural Health Monitoring)기술의 수요 또한 증가하고 있다. 구조물마다 고유한 동특성을 가지고 있으며, 다양한 외력의 영향을 받기 때문에 구조물의 건전성을 평가하는 다양한 방법들이 연구되고 있다. 이상거동 시점이란 구조물이 비정상적 (Abnormal)으로 진동하는 시점으로 손상을 명확히 검출하기 위해서는 이상거동의 시점을 기준으로 전과 후를 비교하여야 한다. 즉, 이상거동은 구조물 손상의 이상 징후이며, 정확한 이상거동 시점의 추정은 구조물의 안전과 직결될 수 있다. 이상 거동은 손상을 유발하고 이는 곧 막대한 경제적 피해 및 심각한 인명 피해로 이어지므로 본 연구에서는 시간-주파수 신호분석 기법인 힐버트-황 변환을 이용한 이상거동 시점 추정 기법을 제안하고 진동대를 이용한 모형실험을 통해 제안한 알고리즘의 검증을 수행하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 지반공학 공동 학술발표회
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• pp.3-14
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• 2005

Reliable predictions of the movement of earth retaining structures and the ground adjacent to braced walls in urban excavation are often difficult due to many variable factors. The ground settlement and the damage of adjacent structures in urban excavation has been an important issue. Therefore, the stability of the adjacent structures must be secured with the excavation support and research on the protection of adjacent structure is necessary. This study showed an urban excavation case and introduce observation method for case of damage behavior in urban excavation.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.697-700
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• 2000

Fatigue damage to reinforced concrete bridge decks have been found in many bridges. Failure mode of most reinforced concrete decks is caused by local punching shear rather than flexural moment due to cumulated damage. In this study, mechanical degradation of unstrengthened and strengthened bridge deck specimens is experimentally investigated. The unstrengthened deck specimens were damaged under the pulsating loading condition. After the test, deteriorated deck specimens were strengthened with Carbon Fiber Sheet, then loaded to observe the improvement of the fatigue behavior. It is shown that fatigue damaged specimens are similar to real bridge rather than static damaged specimens.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
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• pp.119-123
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• 1991

The concrete structures subjected to strong earthquakes may undergo hysteretic behavior and result in severe damage. The inelastic behavior and steffness degradation due to seismic loading must be properly modeled. The present study proposes a realistic model to assess the structural damage of concrete structures under seismic loadings. The present model also takes into account the probabilistic nature of seimic loading and thus the randomness of motion.