• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.4
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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.

• Proceedings of the KSME Conference
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• 2004.11a
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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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.243-252
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• 1987

The propagation and closure behavior of surface crack initiated at a sharply notched specimens were investigated in 5083-H113 aluminium alloy under constant amplitude of tension load by the unloading elastic compliance method. The crack shape (aspect ratio) was found to be approximately semicircular during the crack was being small and to be changed to semi-elliptical during it was being long. The propagation rate of a surface crack initiated from notch root decelerated with increasing crack length when the crack was small and then accelerated when it was large. The effect of stress ratio was large in lower .DELTA.K range, but the effective stress intensity factor range .DELTA.K$_{eff}$ was found to diminish the difference of the crack propagation rate. By considering the increase in crack closure stress with crack length and examining the microphotographs, plasticity-induced and roughness-induced crack closure mechanisms were predominant in the range of this study.y.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.8
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• pp.1536-1544
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• 1992

A relatively simple prediction method is proposed for initially semicircular surface crack growth under axial loading. The method takes into account the difference in surface crack closure behavior at the depth point and at the surface intersection point, and also the relationship of crack closure for surface crack and through-thickness crack. The prediction method provides conservative estimation for fatigue life within factor of two, and the predicted crack geometry variations agree well with the observed results. As a result, the prediction method proposed here is considered to be useful for engineering application.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.125-134
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• 1989

Pseudo-random load waves for fatigue testing were generated by personal computer simulation and preliminary study was performed on the growth behavior of surface fatigue crack under random ladings. The closure behavior and growth rates of surface fatigue crack were significantly influenced by the characteristics of random waves. It was also found that the growth rates of surface fatigue crack under random loadings could not be always described by the effective stress intensity factor based on the concept of crack closure.

• Journal of Mechanical Science and Technology
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• v.16 no.2
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• pp.182-191
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• 2002

The reliable stress intensity factor analysis is required for fracture mechanics design or safety evaluation of mechanical joints at which cracks often initiate and grow. It has been reported that cracks in mechanical joints usually nucleate as corner cracks at the faying surface of joints and grow as elliptical arc through cracks. In this paper, three dimensional finite element analyses are performed for elliptical arc through cracks in mechanical joints. Thereafter stress intensity factors along elliptical crack front including two surface points are determined by the virtual crack closure technique. Virtual crack closure technique is a method to calculate stress intensity factor using the finite element analysis and can be applied to non-orthogonal mesh. As a result, the effects of clearance on the stress intensity factor are investigated and crack shape are then predicted.

• Journal of Korean Society of Steel Construction
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• v.8 no.3 s.28
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• pp.3-11
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• 1996

To investigate the effect of fatigue crack growth due to the surface residual stress, it is measured the residual stress distribution by x-ray diffraction at the crack tip each constant crack growth in the notch specimens, and quantitively assessed the effect of crack closure caused to the distribution of compressive stress at the crack tip from evaluating crack openning stress using the finite element analysis. It is concluded that the degree of the residual stress distribution at the crack tip is decreased with increasing the crack length. From the fact that it is similar to the crack openning stress ratio, it is found that the compressive residual stress distribution and size is related to the crack closure effect and surface residual stress field with propagating crack in the notch specimens depends on the stress intensity factor range at the crack tip.

• Journal of Mechanical Science and Technology
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• v.14 no.5
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• pp.562-568
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• 2000

The pressure in a water-entry induced cavity, is analyzed up to the closed cavity (bubble). Water-entry is a highly transient phenomenon, and the evolution of the water-entry cavity must be explained by considering the entry speed, shape of the solid body, atmosphere pressure, and cavity pressure as the primary variables. This work is an extension of the cavity dynamics model recently reported by Lee (l997a). To extend the model for a wide range of entry speeds the cavity pressure is calculated from a one-dimensional quasi-steady flow model. The estimation of the cavity pressure allows us to explain the experimentally observed surface closure phenomena at low entry speeds. Predictions for the time of surface closure are compared with the published experimental data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.781-789
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• 1988

The fatigue crack growth and crack closure behavior of long through-thickness cracks and small half-penny shaped surface cracks were investigated in 5083-H113 Aluminum alloy under constant amplitude testing by the unloading elastic compliance method. It was found that, in the Region II, the crack growth behavior of both through-thickness and surface cracks exhibited the tri-linear form with two transitions and no concern with stress ratio R. In the Region I $I_{ab}$ and I $I_{b}$, through-thickness cracks grew faster than surface cracks in length direction, but at .DELTA. K .leq.4 MPa.root.m for R=0.1 the growth rates of surface cracks in depth direction, grew faster than those of through-thickness cracks. When the crack closure was considered, the growth rates of through-thickness cracks lay between the growth rates of depth direction and the growth rates of length direction in surface cracks. It is suspected that this was caused by the difference of crack closure at depth and length direction of surface cracks.s.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.36 no.3
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• pp.35-43
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• 2004

Reduction of fresh water consumption and effluent discharge provide diverse advantages in raw materials and energy savings. Papermaking system closure, however, reduces the efficiency of additives, decreases retention and dewatering, and causes many other Problems in papermaking. Accumulation of inorganic and organic substances in the process white water is the prime cause of these problems. Understanding of the accumulation phenomena of the detrimental substances in the papermaking process is of great importance for papermaking system closure. In this study a process simulation method was employed to analyze the accumulation phenomena of anionic starch in the process white water as the reuse rate of dry broke and pick up of surface sizing agent is increased. Steady state simulation studies were carried out based on the model developed in previous study. The variation of dissolved starch concentration in each process unit was monitored as a function of reuse rate of dry broke and surface sizing agent pick up rate. The result showed that dissolved starch concentration Increased as reuse rate of dry broke and surface sizing agent pick up rate was increased.