• 콘크리트학회지
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• 제7권5호
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• pp.145-154
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• 1995

콘크리트는 압축압밀과 인장균열파괴의 두 개의 서로 다른 파괴양상을 타나낸다. 따라서, 다차원의 압밀과 인장균열을 포함하는 콘크리트의 비선형해석을 위하여 두개의 다른 파괴기준을 사용하는 콘크리트 재료모델이 사용되어야 한다. 본 연구에서 사용하는 콘크리트 모델은 소성이론에 기초한 것으로 압축압밀과 인장균열에 대한 다중파괴이론을 사용하고 잇다. 인장균열거동에 대해 두 개의 다른 재료모델이 사용되고 있는데, 이상화된 균열방향에 따라 분류되는 회전균열소성모델과 정지균열소성모델이 사용되고 있다. 본 연구에서는 콘크리트의 비선형거동이 plane stress 문제에 대하여 단순화된다. 이 재료모델은 유한요소해석에 사용되며 그 결과는 몇 개의 철근콘크리트부재 실험과 비교된다. 회전균열소성모델과 정지균열소성모델의 장단점이 비교된다.

• 대한토목학회논문집
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• 제36권6호
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• pp.1109-1116
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• 2016

아스팔트 콘크리트 포장의 반사균열 저항성을 평가하기 위해 다양한 방법이 적용되고 있다. 반복직접인장시험은 기존실험에 비해 저렴하고 간편하게 아스팔트 콘크리트 포장의 반사균열 저항성을 평가할 수 있는 장점이 있다. 국내에 반복직접인장시험을 도입하기 위해서는 파괴기준의 결정이 필요하다. 반복직접인장시험의 파괴횟수를 결정하기 위해 다양한 방법을 검토한 결과 초기하중의 10%일 때를 파괴시점으로 산정할 경우 10% 이내의 반복횟수 편차를 나타내었다. 아스팔트 콘크리트의 두께가 30 mm에서 50 mm로 증가할 경우 파괴횟수는 13.6배 증가하여 포장두께가 반사균열 저항성에 큰 영향을 미치는 것을 알 수 있었다. 또한 재하변형의 크기가 클수록 반사균열의 진전속도가 증가하는 것으로 나타났다. 반복직접인장시험은 포장 두께, 변형크기, 재료적 특성에 따라 반사균열저항성을 정량적으로 평가할 수 있기 때문에 포장설계시 반사균열 저항성 평가 방법으로 적용 가능한 것으로 나타났다.

• Journal of Welding and Joining
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• 제13권4호
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• pp.46-54
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• 1995

The cold cracking susceptibility of a variety of weld metals deposited by GMAW with several kinds of commercial solid wires for high strength-toughness steel was investigated. G-BOP test and LB-TRC test were carried out to study the effects of preheat, chemical composition and hydrogen level on the weld metal cold cracking. The results obtained are as follows. 1) 10% CPT obtained by G-BOP test was the most valuable criteria for evaluating the cold cracking susceptibility of weld metals compared with percentage of cracking at room temperature and crack free temperature, and it had good correlation with the results of LB-TRC test. 2) Cold cracking susceptibility of weld metals was high in the row of MG100A, MG100C, MG100D and MG100B. Welds deposited with MG130 and MG80 showed similar icidents of cracking with MG100C and MG100B respectively, even though their strength levels were different. 3) Diffusible hydrogen level in weld metals which has good relation with hydrogen content in wire itself was the most critical factor for controlling the cold cracking susceptibility of weld metal.

• 대한기계학회논문집A
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• 제21권2호
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• pp.317-326
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• 1997

An investigation was performed to study the matrix cracking and delamination in laminated composite plates due to transverse impact. A model was developed for predicting the initiation of the matrix cracking and the shape and size of impact-induced delamination in laminated composite plates resulting from the ballistic impact. The model consists of a stress analysis and a failure analysis. A transient finite element analysis which was based on the higher-order shear deformation theory was adopted for calculating the stresses inside the laminated composite plates during impact. A failure analysis was used to predict the initial intraply matrix cracking and the shape and size of the interface delamination in the laminates. As a results, a shear matrix cracking which was governed by the transverse interlaminar shear stress occured at the middle layer near the midplane of laminates and a bending matrix cracking which was governed by the transverse inplane stress occured at the bottom layer near the surface of laminates. In a thick laminates, a shear matrix cracking generated first at the middle layer of laminates, but in a thin laminates, a bending matrix cracking generated first at the bottom layer of laminates.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 제7회 압연 심포지엄
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• pp.117-120
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• 2009

The rolling of flat slabs or sheet metal is probably the most advanced technique of metalworking technology. In spite of this very intensive activity, the problem if edge cracking has not been resolved. Although edge cracking is a major industrial problem, relatively little well-documented experimental work has been published on subject. Despite the paucity of exact experiments, it is reasonably certain from published data that three causes contribute to its occurrence; (1) limited ductility of the rolled material (2) uneven deformation at the edges and (3) variations in stresses along the width of the rolled material, particular near the edge. The present study was carried out to show the generation of edge cracking using ductile fracture criteria and FE-simulation. The validity of simulated results was verified by rolling experiments of steel strip.

• Journal of Welding and Joining
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• 제22권3호
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• pp.9-13
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• 2004

지하로부터 채굴되는 천연가스의 황화수소가스 농도가 일정 수준 이상이면 이를 사우어가스(sour gas)분위기라고 하는데, 이러한 분위기에 강재가 노출되면 수소유기균열(hydrogen induced cracking, 이하 'HIC균열'이라고 함)이 발생할 위험성이 높아진다.(중략)

• International Journal of Concrete Structures and Materials
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• 제7권1호
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• pp.79-93
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• 2013

One of the biggest problems affecting bridges is the transverse cracking and deterioration of concrete bridge decks. The causes of early age cracking are primarily attributed to plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. The cracks can be influenced by material characteristics, casting sequence, formwork, climate conditions, geometry, and time dependent factors. The cracking of bridge decks not only creates unsightly aesthetic condition but also greatly reduces durability. It leads to a loss of functionality, loss of stiffness, and ultimately loss of structural safety. This investigation consists of field, laboratory, and analytical phases. The experimental and field testing investigate the early age transverse cracking of bridge decks and evaluate the use of sealant materials. The research identifies suitable materials, for crack sealing, with an ability to span cracks of various widths and to achieve performance criteria such as penetration depth, bond strength, and elongation. This paper also analytically examines the effect of a wide range of parameters on the development of cracking such as the number of spans, the span length, girder spacing, deck thickness, concrete compressive strength, dead load, hydration, temperature, shrinkage, and creep. The importance of each parameter is identified and then evaluated. Also, the AASHTO Standard Specification limits liveload deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas that are subject to pedestrian use. The deflection is found to be an important parameter to affect cracking. A set of recommendations to limit the transverse deck cracks in bridge decks is also presented.

• 콘크리트학회지
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• 제9권2호
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• pp.133-144
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• 1997

2차원 응력상태의 철근콘크리트 부재해석을 위하여 소성이론과 파괴모델의 통합방법을 연구하였다. 콘크리트의 대별되는 두 가지 거동특성인 다차원 압축상태의 강도증가와 인장균열파괴를 동시에 나타내기 위하여, 압축파괴와 인장균열의 다중파괴기준을 사용하는 소성이론을 근간으로 여러 실험결과를 반영하는 파괴모델을 적용한다. 압축파괴기준으로서 Drucker-Prager모델과 von Mises 모델을 비교 사용하며 인장균열거동에 대하여 회전균열소성모델과 고정균열소성모델을 비교한다. 이러한 압축파괴기준과 이장균열파괴기준의 설정에는 다차원 압축상태의 강도증가, 균열로 인한 인장과 압축응력도의 저하, 보강철근의 영향등을 나타내는 실험식과 파괴에너지개념을 사용한다. 이 재료모델을 비선형유한요소해석에 사용하여 기존의 실험결과와 비교한다. 재료모델의 압축파괴와 인장균열거동을 검증하기 우하여 콘크리트의 압축파괴 또는 철근의 인장항복에 의하여 거동이 대별되는 실험들과 비교한다.

• 한국정밀공학회지
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• 제14권7호
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• pp.116-125
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• 1997

An investigation was performed to study the impact damage in CFRP laminated composites subjected to impact loading. A finite element model has been developed for predicting the impact damage in laminated composite plates resulting from the ballistic impact. The finite element model was based on the higher-order shear deformation theory and was used to predict the initial intraply matrix cracking and the shape and size of interface delamination in laminated composites. Numerical simulation was performed and then the initiation of the matrix cracking and the shape and size of impacted induced delamination were predicted, and te results were compared with those of impact experiments with the same dimension and stacking sequences. A linear relationship holds between impact velocity and length and width of delamination. As impact velocity is increased, the increase of delamination length is highger than the increase of delamination width.

• Computers and Concrete
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• 제1권1호
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• pp.61-76
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• 2004

The paper is devoted to present the Continuum Strong Discontinuity Approach (CSDA) and to examine its capabilities for modeling cracking of concrete. After introducing the main ingredients of the CSDA, an isotropic continuum damage model, which distinguishes tension and compression states, is used to implicitly induce a projected traction separation-law that rules the cracking phenomena. Criteria for onset and propagation of material failure and specific finite elements with embedded discontinuities are also briefly sketched. Finally, some representative numerical simulations of cracking, in plain and reinforced concrete specimens, using the CSDA are presented.