• 대한기계학회논문집
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• 제14권6호
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• pp.1576-1582
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• 1990

본 연구에서는 Al 2024-T3 판으로 제작된 한면 노치 시편에 여러 조건의 피로 하중을 가하여 노치면내에 형성된 미소 피로균열의 COD를 광학적 간섭현상에 기초를 둔 미소 변위측정기(Interferometric Strain/Displacement Gage`ISDG)를 개량하여 측 정하였다. 이 ISDG의 컴퓨터 조정방식을 정밀화시켜 0.02$\mu\textrm{m}$까지의 상대변위를 측정 할 수 있도록 보완하였다. 고정밀화돈 측정기로 수십 $\mu\textrm{m}$길이의 미소균열의 COD도 측 정하였고 컴류터에 저장시킴으로써 시험후 미소 피로균열에 대한 열림 특성을 분석할 수 있다. 측정된 미소 피로균열의 균열열림특성을 고찰하고 긴 균열의 열림특성과도 비교.분석 하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.28-32
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• 1995

This effective way for repairing a fatigue crack is making indetations around fatigue crack tip. In this paper, we performed fatigue test to investigate the optimal position of the indentations, and observed crack opening behavior at the same time. The indentation positions of specimens were on the crack tip, front and back of the crack tip. The results of the experiment showed taht it was veryeffective way to increase fatigue life that making indentations on the crack tip, and it was the optimal position that making indentations on the crack tip.

• 대한기계학회논문집
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• 제14권5호
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• pp.1193-1199
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• 1990

본 연구에서는 가공경화지수 (n)가 서로 다른 몇가지 재료를 선택하고 과대하 중의 비 (%PL)를 달리하는 단일 과대하중 피로 시험을 행하여 재료의 가공경화지수가 피로 균열 진파의 지연거동에 미치는 영향과 아울러 균열닫힘현상과의 관계를 구명하였다.

• International Journal of Automotive Technology
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• 제7권3호
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• pp.337-343
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• 2006

Numerical calculations are made in order to find a possible correlation between the J-integral and the crack mouth opening displacement(CMOD) in dynamic nonlinear fracture experiments of 3-point bend(3PB) specimens. Both elastic-plastic and elastic-viscoplastic materials are considered at different impact velocities. The J-integral may be estimated from the crack mouth opening displacement which can be measured directly from photographs taken during dynamic experiments.

• 한국자동차공학회논문집
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• 제8권4호
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• pp.149-157
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• 2000

Computer simulations of the mechanical behavior of a three point bend specimen with a quarter notch under impact load are performed. The case with a load application point at the side is considered. An elastic-plastic von Mises material model is chosen. Three phases such as impact bouncing and bending phases are found to be identified during the period from the moment of impact to the estimated time for crack initiation. It is clearly shown that no plastic deformation near the crack tip is appeared at the impact phase. However it is confirmed that the plastic zone near the crack tip emerges in the second phase and the plastic hinge has been formed in the third phase. Gap opening displacement crack tip opening displacement and strain rate are compared with rate dependent material(visco-plastic material). The stability during various dynamic load can be seen by using the simulation of this study.

• 대한기계학회논문집
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• 제14권6호
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• pp.1568-1575
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• 1990

본 연구에서는 중앙균열을 가진 SB41강의 평판이 하중제어와 변형률제어 피로 상태에서 소규모 항복, 대규모 항복, 또는 전면 항복의 각 응력에서 피로균열 진전 속 도와 J적분 범위, .DELTA.J와의 관계를 조사하는 한편, 피로균열 진전 속도를 지배하는 국 소적 역학 인자인 균열선단 개구변위, COD와 균열 진전 속도와 관계 및 그 특성을 고 찰하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제5권1호
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• pp.195-205
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• 2001

An analytical finite element approach to nonlinear behavior of reinforced concrete shear walls with opening under monotonic loading was presented in this paper. In order to achieve the objectives of present paper, the orthogonal anisotropic models for cracked reinforced concrete element based on smeared crack concept were used as the nonlinear material models of biaxial state of stress. The stiffness of cracked concrete was evaluated through the combined use of tension and compression stiffness models in and parallel directions of crack, respectively and shear transfer effect due to the aggregate interlocking at crack surface. The stress and strain of reinforcement in concrete was evaluated using the average stress and average strain relation with bond effect. based on smeared crack concept. The diagonal reinforcing bar was modeled using truss element with bond effect. A special significance of diagonal reinforcement near opening was given to the shear wall with opening and an effective distribution of diagonal reinforcement was presented in order to give an ultimate strength increment as well as a crack control.

• 대한기계학회논문집A
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• 제31권4호
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• pp.432-440
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• 2007

In this study, we have investigated the closure behavior of fatigue cracks in SAPH440 steel plates under a mixed-mode I+II loading. A crack image capturing system as a direct measuring method was used to measure the closure levels at a crack tip. The crack closure levels in the fluctuation and stable sections were increased with the increase of the mode mixture ratio. The mode mixture ratio independent fatigue crack propagation rates equation was calculated by considering mixed-mode crack closure levels. The equation was examined according to the application method of crack opening ratio. The fracture surface analysis by C-scan method was also performed in order to investigate the closure mechanism and propagation mode of crack under the mixed-mode I+II loading. The crack closure under the mixed mode I+II is confirmed as a surface roughness closure by the quantitative analysis of fracture surface using the proposed surface roughness parameter.

• International Journal of Concrete Structures and Materials
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• 제7권4호
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• pp.253-264
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• 2013

A major difference between high-strength reinforcing steel and conventional steel in concrete is that the service-load steel stress is expected to be greater. Consequently, the service-load steel strains are greater affecting cracking behavior. A parametric study investigating crack widths and patterns in reinforced concrete prisms is presented in order to establish limits to the service-load steel stress and strain. Additionally, based on the results of available flexural tests, crack widths at service load levels were evaluated and found to be within presently accepted limits for highway bridge structures, and were predictable using current AASHTO provisions. A limitation on service-level stresses of $f_s{\leq}414$ MPa (60 ksi) is nonetheless recommended.

• 한국산업융합학회 논문집
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• 제6권4호
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• pp.291-298
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• 2003

Interfacial crack problems between fiber and matrix in composite materials are discussed. A series of interfacial crack initiation and propagation experiments are conducted using the biaxial loading device for various mode-mixes. Normal crack opening displacement (NCOD) is measured near crack front by a crack opening interferometry and used for extracting fracture parameters. From mixed mode interfacial crack initiation experiments, large increase in toughness with shear components is observed. Initial velocity of crack propagation is very dependent upon the mode-mixes. It increased with positive mode-mix due to the increase of stress singularities ahead of crack front and decreased with negative mode-mix resulting from the increase of the degree of compressive stress behind the crack front. Crack propagation was less accelerated with positive mode-mix than the negative mode-mix.