• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.214-219
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• 2004

Crack tip behavior of single mode loading condition(mode I)depend on tensile loading component but one of mixed mode loading condition(mode I+II) have influenced on shear loading component like the practical structure. Because crack closure is caused by shear loading component under mixed-mode loading a research on the behavior in the stage of crack initiation and propagation require to be evaluate about crack closure effect by fatigue crack surface friction. For that reasion we examined the behavior at the crack tip by direct measuring method. Measured behavior at the crack tip was analyzed through vector crack tip displacement. As a result, crack propafation equation was corrected by considering with crack closure effect. In addition we compared fatigue fracture crack surface and crack closure level.

• 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.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2001년도 봄 학술발표회 논문집
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• pp.365-372
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• 2001

This study is concerned with the application of an analytical model of cyclic crack growth that includes the effects of crack closure. The crack closure model is based on the Dugdale model and the strip model, considering the plasticity-induced closure which is caused by residual plastic deformation remaining in the wake of an advancing crack. This study is performed to get the relation between crack growth and crack opening stress with the constant stress ratio, and the relation between stress ratio and crack opening stress with the constant maximum stress under constant-amplitude loading. Under constant-amplitude loading, the crack opening stress is conversed the constant value as a crack grows and is proportion to both the stress ratio and the maximum stress. The crack closure effect, however, is decreased in the positive stress ratio and disappeared at about 0.7. The crack growth analysis using the crack closure model shows that the influence of stress ratio is minimized in the relation between crack growth ratio and effective stress intensity range specially at the negative stress ratio.

• 대한기계학회논문집A
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• 제25권5호
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• pp.797-804
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• 2001

To obtain representative fatigue crack growth characteristic curve in residual stress field, fatigue crack growth test was carried out at various stress ratio and fatigue crack growth characteristic curve was represented using crack closure concept. Obtained results are as follows;K(sub)op/K(sub)max was independent of K(sub)max when R was lower than 0.5 and crack closure phenomenon was not observed when R is higher than 0.5. therefore neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated. Thus, considering crack closure phenomenon, fatigue crack growth characteristics curve of A 106 Gr B Steel weldment can be effectively estimated.

• 한국정밀공학회지
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• 제14권7호
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• pp.82-90
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• 1997

When a structure is made by the process of forging, it has the different mechanical properties from those it has before the process. This study is based on the crack closure phenomenon of the crack growth behavior of forged AI7050-T7452. The specimens were prepared in three kinds of forging ratio in order to find out the effects of crack closure on the forged material and compare the crack growth behavior with not-forged aluminum. COD method and strain gage method were used in measuring the crack closure stress and the results from those methods were compared each other. FEM analysis was applied to verify the effective stress intensity factor range by the superposition of the crack closure load to the crack tip. In the result of this study, the crack closure stress decreased with increasing the forging ratio due to the finer grain size and the brittle manner.

• 대한기계학회논문집
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• 제10권6호
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• pp.898-905
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• 1986

본 논문에서는 강의 피로균열진전거동과 미시조직과의 관계를 밝히기 위한 연 구의 일환으로 제이상 마르텐사이트 중에 모상 페라이트가 존재하는 복합조직강을 준 비하여 이들 강의 제이상 경도변화에 따른 피로균열진전저항을 균열휨과 균열닫힘을 통하여 검토하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.79-84
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• 2000

Crack closure and growth behavior of physically short fatigue cracks under random loading are Investigated by performing narrow- and wide-band random loading tests for various stress ratios. Artificially prepared two-dimensional, short through-thickness cracks are used. The closure behavior of short cracks under random loading is discussed, comparing with that of short cracks under constant-amplitude loading and also that of long cracks under random loading. Irrespective of random loading spectrum or block length, the crack opening load of short cracks is much lower under random loading than under constant-amplitude loading corresponding to the largest load cycle in a random load history, contrary to the behavior of long cracks that the crack opening load under random loading is nearly the same as or slightly higher than constant-amplitude results. This result indicates that the largest load cycle in a random load history has an effect to enhance crack opening of short cracks.

• 한국자동차공학회논문집
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• 제13권3호
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• pp.178-185
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• 2005

Crack tip displacement is originated by tensile stress component, s and shear stress component, t on pure Mode I and pure Mode II. The crack tip displacement(CTD) depends on combined types of different two stress components under mixed-mode loading conditions (MMLC). Thus, the analysis of crack tip displacement must be CTD vector, dv which is composition of ds and dt under MMLC. In this paper, various effects of MMLC on the crack closure are studied experimentally. The crack closure magnitude is calculated from the information of crack tip displacement under MMLC. This information has been obtained from the high resolution optical microscope in direct observations of crack displacement behavior at the crack tip. Observed crack tip displacement is analyzed by using CTD vector to determine crack opening load. The various effects of MMLC on the crack closure are explained using crack opening ratio with crack length and mode mixture. The effective stress intensity factor considering crack closure is also discussed.

• 대한기계학회논문집
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• 제11권2호
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• pp.243-252
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• 1987

본 논문에서는 작은 인공결함을 가진 표면균열의 진전거동을 밝히기 위하여 용접성이 좋고 강도도 적당하며 내식성이 좋아 해양구호무재 및 용접구호물재로서 널 리 사용되는 5083-H113 알루미늄합금을 준비하고 이재료의 피로표면균열 진전거동에 미치는 응력비의 영향을 균열닫힘과 함께 검토하였다.

• Journal of Mechanical Science and Technology
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• 제18권11호
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• pp.1989-1995
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• 2004

Finite element analysis(FEA) is the most popular numerical method to simulate plasticity-induced fatigue crack closure and can predict fatigue crack closure behavior. Finite element analysis under plane stress state using 4-node isoparametric elements is performed to investigate the detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The mesh of constant size elements on the crack surface can not correctly predict the opening level for fatigue crack as shown in the previous works. The crack opening behavior for the size mesh with a linear change shows almost flat stress level after a crack tip has passed by the monotonic plastic zone. The prediction of crack opening level presents a good agreement with published experimental data regardless of stress ratios, which are using the mesh of the elements that are in proportion to the reversed plastic zone size considering the opening stress intensity factors. Numerical interpolation results of finite element analysis can precisely predict the crack opening level. This method shows a good agreement with the experimental data regardless of the stress ratios and kinds of materials.