• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.6
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• pp.53-60
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• 2008

The cross-sections of continuous multi-span beams sometimes suddenly increase, or become stepped, at the interior supports of continuous beams to resist high negative moments. The three-dimensional finite-element program ABAQUS (2007) was used to analytically investigate the inelastic lateral-torsional buckling behavior of stepped beams subjected to linear moment gradient and resulted in the development of design equations. The ratios of the flange thickness, flange width, and stepped length of beam are considered for the analytical parameters. Two groups of 27 cases and 36 cases, respectively, were analyzed for doubly and singly stepped beams in the inelastic buckling range. The combined effects of residual stresses and geometrical imperfection on inelastic lateral-torsional buckling of beams are considered. First, the distributions of residual stress of the cross-section is same as shown in Pi and Trahair (1995), and the initial geometric imperfection of the beam is set by central displacement equal to 0.1% of the unbraced length of beam. The new proposed equations definitely improve current design methods for the inelastic lateral-torsional buckling problem and increase efficiency in building and bridge design.

• Journal of Dental Rehabilitation and Applied Science
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• v.20 no.2
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• pp.109-120
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• 2004

INTRODUCTION: The build-up method has been used for application of porcelain powder on the metal framework to make final tooth shape conventionally. This method takes time and need skill to mimic final shade and shape of porcelain fused to metal crown. The purpose of this study was to develop standard shape and shade laminating porcelain forms to reduce build-up time. METHODS: To make tooth form porcelain paste, several liquid organic compounds were added to conventional feldspathic porcelain. The amount of additives and rheologic property were tested to find out best composition. Comparison of mixing methods to reduced porosity, proper heating schedule, and measurement of shrinkage amount and residual organic materials were performed to set-up standard procedures. Finally, biaxial flexural strength and color of preformed laminated paste porcelain were compared with those of porcelain which fabricated by the conventional build-up method. RESULTS: There was no significant difference in physical properties and color stability between two fabrication methods after various testing methods. Conclusion: This new build-up method can be applied to fabricate the PFM crown and bridge without any loss of strength and optical properties.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.874-880
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• 2003

The effect of h-BN content on microstructure, mechanical properties, and machinability of AlN-BN based machinable ceramics were investigated. The relative density of sintered compact decreased with increasing h-BN content. The four-point flexural strength also decreased from 238 MPa of monolith up to 182 MPa by the addition of 30 vol％ h-BN. Both low Young's modulus and residual tensile stress, formed by the thermal expansion coefficient difference between AIN and h-BN, might cause the strength drop in AlN-BN composite. The crack deflection, and pull-out phenomena increased by the plate-like h-BN. However, the fracture toughness decreased with h-BN content. The second phases, consisted of YAG and ${\gamma}$-Al$_2$O$_3$, were formed by the reaction between Al$_2$O$_3$ and Y$_2$O$_3$. During end-milling process, feed and thrust forces measured for AlN-(10～30) vol％ BN composites decreased with increasing h-BN particles, showing excellent machinability. Also, irrespective of h-BN content, relatively good surfaces with roughness less than 0.5 m (Ra) could be achieved within short lapping time.