• Journal of the Korean Society of Safety
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• v.5 no.1
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• pp.19-29
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• 1990

The objective of this paper is to investigate the effect of residual stresses on the $\Delta$K$\sub$th/ and fatigue crack growth behavior of butt weldments. For this purpose, transverse butt sutmerged arc welding was performed on SM50A steel plate and CT(compact tension) specimens which loading direction is perpendicular to weld bead were selected. Welding residual stresses distribution on the specimen was determined by hole drilling method. The case of crack located parallel to weld bead, the states of as weld and PWHT, $\Delta$K$\sub$th/ of specimens(HAZ, weld zone) was higher than that of the base metal probably because of the compressive residual stresses of crack tip. In low $\Delta$K region, it is estimated that the effects of residual stresses for da/dN are great. In region II, the da/dN of weldments in as weld state was lower than that of the base metal. Though da/dN of Weldments in PWHT state was similar to that of the base metal. The constant of power law, m in two states consisted with the base metal. Therefore , it is estimated that the value of m is not affected by residual stresses. Fatigue crack growth behavior of weldments consisted with the base metal considering the effective stress intensity factor range($\Delta$K$\sub$eff/) included the effect of initial residual stress(Kres). Thus, we can predict the fatigue crack growth behavior of weldment by knowing the distribution of initial residual stress at the crack tip.

• 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.

• Proceedings of the KWS Conference
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• 1999.05a
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• pp.237-240
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• 1999

In this study, residual stresses of the weldment were calculated by finite element analysis(FEA) and experiment. And, the crack closure behaviour and fatigue crack growth characteristics in field of residual stress of A106 Gr B steel pipe weldment were investigated under various stress ratio. Obtained results are as follows. I) $K_{op}$ was independent of $K_{max}$, and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure. and 3) Neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated' and Actual fatigue crack growth rate can be overestimated by $K_{res}$, in tensile residual stress field.

• Publications of The Korean Astronomical Society
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• v.8 no.1
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• pp.243-263
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• 1993

One hundred forty two digital spectra of 110 standard stars with 1 A resolution in ${\lambda}{\lambda}\;3000\;A\;{\sim}4150\;A$ region were analyzed to determine the spectral indices sensitive to the atmospheric parameters. The standard stars cover the temperature in the range of $T_eff$ from ${\sim}4000^{\circ}$ to ${\sim}7000^{\circ}\;K$ and the surface gravity in the range of log g from 0 to 5 and the metal abundance [Fe/H] from -2.7 to 0.4. We have derived physical parameters, theta(=T/5040), log g, and [Fe/H] for the standard stars using indices, P(38/93), Fe I(A), Fe I(B), SrII, and $H{\delta}$, with overall accuracies of 0.067, 0.617, and 0.466, respectively. However for some region of spectral type and metallicity, those can be obtained with better accuracies. Those indices are found to be useful especially for stellar gravity determination.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.57-64
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• 1997

Fatigue crack propagation behaviors and life prediction for SUS 321 plate and its electron beam weld metal were investigated using compact tension specimens. The larger the stress ratio is, the faster the crack propagates, but the variation of crack propagation rate decreases. The effect of stress ratio is greater in the slow crack propagation area than in the faster one. The crack propagation rate of electron beam weld metal is faster than that of base metal because of hardening, weld defect and residual stress in welding area. The crack propagation rate of transverse weld metal has a lower than that of base metal due to the effect of residual stress, but in the time of passing through welding area, has a higher rate. The crack propagation rate using $\Delta$K$_{eff}$ can be well plotted regardless of stress ratio. The fatigue life prediction method of considering crack closure more exactly predicts fatigue life than conventional one. conventional one.e.

• Korean Chemical Engineering Research
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• v.47 no.6
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• pp.720-726
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• 2009

Hydrodynamic similarity was investigated in pressurized three-phase slurry bubble columns by selecting the bubble holdup and pressure drop as objective functions, for the effective design and scale-up of it. In addition, effects of operating variables on the bubble holdup with variation of column diameter were also analyzed. Gas velocity($U_G$), viscosity(${\mu}_{SL,eff}$) and surface tension(${\rho}_{SL}$) of slurry phase, density difference between the slurry and gas phases(${\rho}_{SL}-{\rho}_G$) depending on the operating pressure, pressure drop per unit length(${\Delta}P/L$), column diameter(D) and gravitational acceleration(g) were chosen as governing parameters in determining the bubble holdup and pressure drop in the column. From the dimensional analysis, four kinds of dimensionless groups were derived from the 7 parameters and 4 fundamental dimensions. Effects of dimensionless groups such as Reynolds, Froude and Weber numbers on the bubble holdup in the column were discussed. The pressure drop and bubble holdup could be predicted from the correlation of dimensionless groups effectively, which could be used as useful information for the design and scale-up of pressurized slurry bubble columns.

• Journal of the Korean Society for Precision Engineering
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• v.9 no.1
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• pp.106-117
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• 1992

In this study, the propagation behaviour and the closure phenomena of physically small surface cracks were investigated by the techinque of the Kikukawa-unloading elastic compliance method using a back face strain gage. The surface cracks initiated and propagated from notched specimens under constant amplitude bending load. The crack shape (aspect ratio) with approximately semi-circular at the early stage was changed to semi-elliptical as the cracks grew larger. The crack depth (a) could be expressed uniquenly by the crack length (c). The dependence of the crack propagation rate on the stress ratio R was strongly related in the lower ${\Delta}K$ range. The deceleration of the surface crack propagation rate was prominent in lower R during the crack length was small. When the propagation rate was rearranged with the effective stress intensity factor range ${\Delta}$K_{eff} the dependence of the crack propagation rate on the stress ratio R was found to be diminshed. These were caused by the crack closure phenomena that was most prominent at the lower propagation rate. The mechanism of crack closure phenomena was dominated by the plasticity-induced mechanism.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04a
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• pp.51-52
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• 2008

A single gap transflective liquid crystal display(LCD) driven by fringe electric field in the transmissive(T) region and vertical electric field in the reflective(R) region was designed. Because the pretilt angle is formed in $53^{\circ}$ through polymerization of an UV curable reactive mesogen(RM) monomer at the surface, the effective cell retardation $(d{\Delta}n_{eff})$ value of the R region becomes half of that in the T region where the LCs are homogenously aligned. Consequently, a transflective display driven by a vertical and fringe electric field with a single cell gap and single gamma curves is realized.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1841-1846
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• 2000

To examine the effect of acid fog on the corrosion fatigue behavior in structural steel, fatigue tests under acid fog atmosphere were carried out in comparison with distilled water. The corrosive c omponents contained in acid fog pile up the corrosion products on crack face and show a crack branching and crack tip blunting. Therefore, due to these workings crack growth rate was reduced by decreasing the effective stress range in crack tip rather than under distilled water. Also the effect of sulfuric acid, which is the main component of acid fog, and testing speed on fatigue crack growth were examined. It was found that corrosion behavior was remarkably dependent upon pH and Hz rather than components of acid fog. According as pH and testing speed decrease below a specific value, crack growth was accelerated in comparison with distilled water. This reveals that due to liquid having strong acidity and slow speed of test the crack face dissolution was promoted, so crack closure was disturbed in the process of stress descent.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.79-86
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• 1998

The effect of specimen thickness on fatigue crack growth behavior has been carried out by compact tension specimens of thickness of 3mm, 10mm and 25mm for maraging steel and Al 7075-T6. The closure points were determined during the test by means of a clip-gage situated at the notch mouth. Specimen thickness have no apparent influence on the fatigue crack growth rate of maraging steel, but the crack growth rate of 25mm thickness specimen for Al 7075-T6 is faster than that of 3 and 10mm specimens. The difference of crack growth rates can be successfully explained by considering the different stress state of plane strain and plain stress due to the variation of specimen thickness. Also the crack opening ratio of 25mm specimen is greater than those of 3 and 10mm specimens. When a side groove is introduced in a 10mm specimen, the crack growth rate is approximately similar to that of 25mm specimen. The effective thickness expression of $B_e=B_o-(B_o-B_N)^2B_o$ is the most appropriate to evaluate the crack growth rate of side-grooved specimen. Fatigue crack growth rates can be well described by $\Delta K_{eff}$ of the crack closure points in regardless of all thickness and side-grooved specimens.