• Journal of the Korean Society for Precision Engineering
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• v.17 no.5
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• pp.168-172
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• 2000

The stiffened panel is representative of a large portion of aircraft construction and therefore has much practical importance. In this paper, the influence of various shape parameters on the stress intensity factors and the fatigue crack growth in the panels with bonded composite stiffeners are studied experimentally. Results are presented as crack growth rates for various values of crack lengths, stiffness ratios, and stiffening Materials.

• Journal of the Korean Society of Safety
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• v.8 no.4
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• pp.47-53
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• 1993

The growth of short cracks can be well described in terms of the effective stress intensity factor range, which is calculated on the base of crack closure. The relation between the crack opening SIF and crack length is determined from the experimental results. The crack opening SIF of short cracks, Kop, can be predicted from the crack opening SIF at threshold of long crack, Kop.L. The growth rate of short cracks at notch root can be predicted from the crack opening SIF of short cracks, Kop, and the growth equation of long cracks in region II.

• Journal of Mechanical Science and Technology
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• v.17 no.3
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• pp.343-349
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• 2003

The fuselage-wing intersection suffers from the cyclic bending moment of variable amplitude. Therefore, the influence of cyclic bending moment on the delamination and the fatigue crack propagation behavior in AFRP/Al laminate of fuselage-wing was investigated in this study. The cyclic bending moment fatigue test in AFRP/Al laminate was performed with five levels of bending moment. The shape and size of the delamination Lone formed along the fatigue crack between aluminum sheet and aramid fiber-adhesive layer were measured by an ultrasonic C-scan. The relationships between da/dN and ΔK, between the cyclic bending moment and the delamination zone size, and between the fiber bridging behavior and the delamination zone were studied. As results, fiber failures were not observed in the delamination zone in this study, the fiber bridging modification factor increases and the fatigue crack growth rate decrease and the shape of delamination zone is semi-elliptic with the contour decreasing non-linearly toward the crack tip.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.53-60
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• 1997

The roasting of pyrite with a cyclone reactor have been studied in terms of investigating the reaction behavior of pyrite. The development of a fundamental model for pyrite oxidation and lime sulfation in a vertical cyclone reactor. The model assumes a chemical control shrinking core behavior for the pyrite and a fluid film control shrinking core behavior for the lime. The oxygen and sulphur dioxide concentrations and the energy balance for the gas, pyrite and lime particles are solved. The model was solved and characterized numerically. Experiments have been performed to study the influence of reaction parameters such as reactor temperatures, pyrite particle sizes, air flow rates, feeding rates, and mixing ratio of pyrite and lime. The oxidation and sulfation products were characterized chemically and physically.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03a
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• pp.18-21
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• 1999

The wrinkling of thin sheet metal induced by compressive instability is one of major defects in sheet metal forming processes. compressive instability is influence by many factors such as mechanical properties of the sheet material geometry of the sheet contact conditions and plastic anisotropy. The analysis of compressive instability in a plastically deforming body is rather difficult because the effects of the above-mentioned factors are rather complex and the instability behavior may show swide variations even for small deviations of the factors. in this work the bifurcation theory is introduced for the finite elemental analysis of the instability behavior of a thin sheet with initially sound geometry and property. All the above-mentioned factors are conveniently considered by the finite element method. The instability limit is found by introducing a criterion scheme into the incremental analysis and the post-bifurcation behavior is analyzed by introducing the branching scheme. Wrinkling initiation and growth in the deep drawing process are analyzed.

• Journal of Mechanical Science and Technology
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• v.14 no.4
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• pp.401-407
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• 2000

An elastic-plastic finite element analysis is performed to investigate detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The finite element analysis performed under plane stress using 4-node isoparametric elements can predict fatigue crack closure behavior. The mesh of constant element size along crack surface can not predict the opening level of fatigue crack. The crack opening level for the constant mesh size increases linearly from initial crack growth. The crack opening level for variable mesh size, is almost flat after crack tip has passed the monotonic plastic zone. The prediction of crack opening level using the variable mesh size proportioning the reversed plastic zone size with the opening stress intensity factors presents a good agreement with the experimental data regardless of stress ratios.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.786-789
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• 1997

Ti-6Al-4V has been used widely in biomedical field. But because of its toxicity, the ${\beta}$ stabilizing element, V, in Ti-6Al-4V has been replaced by Nb, Ta. Ti-10Ta-10Nb has been developed for biomedical applications. The fatigue crack propagation behavior of Ti-alloy(Ti-10Ta-10Nb) was investigated, in comparison with that of pure Ti. In order to better understand the fundamental fatigue behavior of Ti-10Ta-10Nb, rotating bending fatigue tests have been carried out. Ti-10Ta-10Nb has a better fatigue strength than pure Ti. In this paper, fatigue life has been predicted with Nisitani's equation of the fatigue crack propagation that can be established by measuring fatigue crack growth rates.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06b
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• pp.129-153
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• 1996

In aqueous slurry processing of silicon nitride, the interaction of dispersant and binder on the surface of particles was studied to identify the effect of these additives on ceramic powder processing. Polymethacrylic acid (PMAA) and polyvinyl alcohol (PVA) were used as dispersant and binder, respectively. the adsorption isotherms of PMAA and PVA for the silicon nitride suspension were determined, while the adsorption of PMAA was differentiated in the mixed additive system by ultraviolet spectroscopy. These experiments were done in order to investigate the effect of these organic additives on the physicochemical properties of silicon nitride suspensions. The electrokinetic behavior of silicon nitride was subsequently measured by electrokinetic sonic amplitude (ESA). As PMAA adsorbed onto silicon nitride, the isoelectric point (pHicp) shifted from pH=6.7 to acidic pH, depending on the surface coverage of PMAA. However, adsorption of PVA did not change the pHicp of suspensions, but did decrease the surface potential of silicon nitride moderately. The rheological behavior of silicon nitride suspensions was measured to assess the stability of particles in aqueous media, and was correlated with the electrokinetic behavior and adsorption isotherm data for silicon nitride.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.525-526
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• 2006

Calcium-hexaluminate phase $(CA_6)$ is known to be effective for the crack shielding due to the spinel block crystal structure. In this study, we focused to the control of $CA_6$ morphology for good damage tolerance behavior in alumina and zirconia/calcium-hexaluminate $(CA_6)$ composites. Calcium-hexaluminate $(CA_6)$ composites were prepared from zirconia, alumina and calcium carbornate powders. Calcium-hexaluminate $(CA_6)$ phase was obtained by the solid reaction through the formation of intermediate phase $(CA_2)$. $CA_6$ phase showed the column type abnormal grain grown behavior composed of small blocks. Due to the typical microstructure of $CA_6$, alumina and zirconia/calcium-hexaluminate composites provide a well controlled crack propagation behavior.

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.313-319
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• 1992

The mechanisms of fatigue crack growth (FCG) in a Ti$_3$Al-based (${\alpha}_2$) alloy, Ti-24Al-11Nb (a/o) with acicular microstructure were studied with particular attention focused on the fatigue crack path through the microstructure and on the effects of specimen orientation and crack closure. The results showed that the fatigue cracks of Ti-24Al-11Nb alloy grew much faster than conventional titanium alloys, with little difference in FCG rates for TL and TS orientations. The fatigue crack paths revealed crystallographic transgranular fracture with frequent serrations and branching. This is in agreement with the known effects of slip planarity and microstructure on the FCG behavior. The load-displacement hysteresis loops showed that the crack closure influenced the FCG behavior.