• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.227-232
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• 2002

This paper describes a calculation of an average crack spacing and the maximum crack width for the high-strength concrete tensile and flexural members. Based on the uniform bond stress distribution of the average steel and concrete strains over the transfer length, the crack spacing and the crack width are proposed to utilize influence of the concrete strength and the cover thickness. This analytical results presented in this paper indicate that the proposed equations can be more effectively estimated the maximum crack width and the average crack spacing of the reinforced concrete flexural and tensile members.

• Structural Engineering and Mechanics
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• 제26권1호
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• pp.99-109
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• 2007

A cracked composite specimen, comprised of an epoxy and an aluminium plate, was fractured under a tensile load. In this paper, two crack configurations were investigated. The first was an artificial center crack positioned in the epoxy plate parallel to the material interface. The other was for two edge cracks in the epoxy plate, again, parallel to the interface. A tensile test was carried out by gradually increasing the applied load and it was verified that the cracks always moved suddenly in an outward direction from the interface. The d/a ratio was gradually reduced to zero, and it was confirmed that the maximum stress intensity factor value for the artificial center crack, $K_{{\theta}{\theta}}^{max}$, approached that of an artificial interface crack,$K_{{\theta}{\theta}}^{ifc\;max}$ (where: 2a is the crack length and d is the offset between the crack and interface). The same phenomenon was also verified for the edge cracks. Specifically, when the offset, d, was reduced to zero, the maximum stress intensity factor value, $K_{{\theta}{\theta}}^{max}$, approached that of an artificial interface edge crack.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.182-187
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• 2000

The application of fracture mechanics have traditionally concentrated on cracks leaded by tensile stresses, and growing under an opening or mode I mechanism. However, many cases of failures occur from growth of cracks subjected to mixed mode loading. Several criteria have been proposed regarding the crack growth direction under mixed mode loadings. This paper is aimed at prediction of fatigue crack growth behaviour under mixed mode(I+II) in two dimensional branched type precrack. In this paper, the maximum tangential stress(MTS) criterion was used to predict crack growth direction. Not only experiment but also finite element analysis(FEA) was carried out. The theoretical predictions were compared with experimental results in this paper

• 대한기계학회논문집A
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• 제26권9호
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• pp.1746-1752
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• 2002

Fatigue fracture in machine components is produced by surface micro-crack from stress concentration area such as notch and material defect. It is difficult to predict the remaining fatigue lift of mechanical components because the surface micro-crack on critical area initiates and grows with statistical distribution. Plane bending fatigue tests were carried out on the plain specimen of Al 2024-T3 and the initiation and growth behavior of surface micro cracks were observed. The statistical distribution of surface length of multiple micro cracks and their maximum length were investigated. The maximum surface crack length distributions were analyzed on the basis of the statistics of extremes in order to examine the prediction of remaining life.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3408-3414
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• 1996

This paper investigated plane strain stress intensity factors caused by thermal impact on a center-crack strip. The crack was aligned perpendicularly to the strip boundary. The problem was analysed by determining the dislocation density function in the singular integral equations formulated by the dislocation theory. Under the abrupt temperature change along the edge, the center crack behaved as a mode I crack due to the symmetric geometry. The value of maximum stress intensity factor monotonically increased until the ratio of dimensionless crack length approached to about 0.3, followed by gradual decrease. As a result, a critical corresponding crack length was determined.

• 한국정밀공학회지
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• 제27권3호
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• pp.80-88
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• 2010

A simple computational model for modeling of subsurface crack growth under cyclic contact loading is presented. In this model, it is assumed that the initial fatigue crack will initiate in the region of the maximum equivalent stress at certain depth under the contacting surface. The position and magnitude of the maximum equivalent stress are determined by using the equivalent contact model, which is based on the Hertzian contact conditions with frictional forces. The virtual crack extension method is used for simulation of the fatigue crack growth from the initial crack up to the formation of the surface pit due to contact fatigue. The relationships between the stress intensity factor and crack length are then determined for various combinations of equivalent contact radii and loadings.

• 한국해양공학회지
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• 제7권2호
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• pp.57-67
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• 1993

The fracture behavior of plain woven glass/epoxy composite plates with a crack is investigated under static tensile loading. It is shown in this paper that the characteristic length associated with the point stress criterion depends on the crack length. To predict the not ched tensile strength, the point stress criterion proposed by Whitney and Nuismer are modified. An excellent agreement is found between the experimental results and the analytical prediction of the modified point stress criterion. The condition of unstable crack growth in the presence of a per-existing flaw(machined notch) is examined by means of the maximum stress intensity factor $K_max$ using maximumload P$_max$. The values of $K_max$ evaluated from energy release rate G$_max$(the compliance me thod) indicate a wide difference. Therefore in regard to anisotropy and heterogeneity of the composite materials studied, the modified shape correction factor f(a/W) is obtained. $K_max$evaluated by the compliance method a little or insignificantly depends on the initial crack length a, the specimen thickness B, the crack angle .theta. and the specimen geometry.

• 한국유기농업학회지
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• 제24권4호
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• pp.699-717
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• 2016

본 연구는 시설하우스 재배에서 앞그루작물 재배 시 형성된 두둑을 재활용하여 뒷그루 작물을 무경운으로 재배할 경우 토양의 이화학성과 생육 및 수량에 미치는 영향을 구명하고자 추진한 연구 결과의 일부이다. 중동통(jd)의 두둑에서 토양 균열은 관찰되었으나 고랑에서는 관찰되지 않았다. 관행 경운 토양 두둑의 길이 방향으로 경운 5개월 후에 최대 폭 30 mm, 최대 깊이 15.3 cm, 길이 37~51 cm 정도 되는 균열이 3개 정도 발생되었다. 그리고 두둑의 폭 방향에서는 길이 7~28 cm 정도 되는 균열이 7.5개 정도 발생되었다. 무경운 1년차는 두둑의 길이 방향에서 최대 폭 18 mm, 최대 깊이는 30 cm, 길이는 140~200 cm 정도 되는 균열이 1개 정도 발생되었으며, 두둑 폭 방향의 균열은 최대 폭 22 mm, 최대 깊이는 18.5 cm에 길이는 6~22 cm 정도 되는 균열이 11개 정도 발생되었다. 한편 모래함량이 많은 중동통(jd)의 무경운 2년차 토양에서 균열은 관찰되지 않았으나, 점토함량이 많은 지산통(jd) 무경운 7년차 토양에서는 균열이 관찰되었다. 중동통(jd) 시설재배의 미사질양토의 관행 경운토양 표토 1 cm 깊이의 관입저항은 59 kPa에 비하여 무경운 1년차는 유의적으로 높았다. 경운 토양 20 cm 깊이의 관입저항은 161~185 kPa 수준이었고 36~39 cm 깊이의 관입저항 503~507 kPa을 정점으로 감소되었다. 무경운 1년차 토양 관입저항은 5~30 cm 깊이까지 167~172 kPa을 유지하였으나, 43 cm 깊이에서 437 kPa를 최대값으로 감소되었다. 무경운 2년차 표토의 관입저항은 1 cm 깊이의 81 kPa에서 6 cm 깊이는 243 kPa로 직선적인 증가를 하였다. 논에서 전환한 지산통(ji) 시설 재배지의 관행 경운 토양 관입저항은 표토 1 cm 깊이로부터 52 cm 깊이까지 토양이 깊어짐에 따라서 직선적인 증가를 하였으나, 그 이상의 깊이에서는 증가되지 않았다. 그러나 두둑을 재활용한 무경운 7년차 토양의 표토 1 cm와 2 cm 깊이의 관입저항은 직선적인 증가를 보여 경운 토양에 비하여 현저하게 증가되었으나, 그 이상의 깊이에서는 거의 변동이 없었다. 지산통(ji)과 중동통(jd)의 쟁기 바닥층은 표토에서 10~12 cm 깊이, 작토층은 21 cm 깊이까지로 추정되었다. 그러나 지산통(ji)의 경운 토양의 경반층은 33~35 cm 깊이로 추정되었으나 무경운 7년차는 경반층이 토양 38~44 cm 깊이에서 흔적으로만 존재하였다. 표토의 수분함량은 관행 경운 토양과 두둑을 재활용한 무경운 토양에서 경운 방법 간에 차이가 없었으나, 20 cm 깊이의 무경운 토양 수분함량은 14%로 경운 토양 25%에 비하여 현저하게 낮았다. 1 Bar와 15 Bar에서 측정한 표토의 보수력은 관행 경운토양 비하여 두둑을 재활용한 무경운 1년차와 무경운 2년차에서 증가되었다. 그리고 무경운 2년차 심토의 보수력은 1 Bar와 3 Bar에서 경운 토양과 무경운 1년차에 비하여 증가되는 경향이었다.

• 한국소음진동공학회논문집
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• 제19권12호
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• pp.1281-1288
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• 2009

Variation of dynamic characteristics of a low pressure turbine blade with crack length is studied in this paper via both experiments and finite element model. Since most of the turbine blades used in domestic power plants are imported from abroad, it is necessary to understand their dynamic behavior in advance. When experimentally obtained natural frequencies and mode shapes are compared with those from FEM results, they are close to each other in their magnitude. Then, it is more feasible to use finite element model for analyzing the dynamic characteristics of a blade under various operation conditions (rotation speed, temperature, etc) as well as with a crack in the blade.

• Journal of Mechanical Science and Technology
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• 제14권3호
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• pp.314-319
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• 2000

Back-face strain compliance (BFS compliance) for the four-point bend specimen has been calibrated for various crack length ratios. Finite element technique was employed to simulate four-point loading and calculate back-face strain of the bend specimen. The numerically determined strain variation along the back face indicates that the sensitivity to gage placement increases with crack length and back-face strain at the gage length less than O.2W, where W is the width of the bend specimen, can be measured within 5% deviation of the maximum BFS. Non-dimensional back-face strain compliance, -E'BCW, was calibrated with FE analysis and experiment. The experimentally determined compliance indicates good agreement with the numerical compliance and can be expressed as a function of crack length ratio.