• Journal of Korean Society of Coastal and Ocean Engineers
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• v.2 no.2
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• pp.59-66
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• 1990

Various types of ice distribution under low temperature greatly influence the environment of the Arctic and Antarctic Oceans. To understand fundamentals of ice properties such as Polar glaciers, icebergs and sea ice, this study focuses on the material behaviors and failure mechanisms of polycrystalline ice. Utilizing the continuum damage theory, a three-dimensional constitutive model to describe creep deformation characteristics in the glacial flow is developed in consideration of micro-cracking as the major physical process of ice deformation. The numerical model is compared with the published experimental data especially in uniaxial constant stress creep tests. The model can simulate primary and secondary creeps as well as tertiary creep characteristics due to the microcrack accumulation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.386-402
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• 2012

In this paper, a method to estimate ice loads as a function of the buttock angle of an icebreaker is presented with respect to polycrystalline freshwater ice. Ice model tests for different buttock angles and impact velocities are carried out to investigate ice pressure loads and tendencies of ice pressure loads in terms of failure modes. Experimental devices were fabricated with an idealized icebreaker bow shape, and medium-scale ice specimens were used. A dry-drop machine with a freefall system was used, and four pressure sensors were installed at the bottom to estimate ice pressure loads. An estimation equation was suggested on the basis of the test results. We analyzed the estimation equation for design ice loads of the International Association of Classification Societies (IACS) classification rules. We suggest an estimation equation considering the relation between ice load, buttock angle, and velocity by modifying the equations given in the IACS classification rules.

• Journal of Ocean Engineering and Technology
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• v.4 no.2
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• pp.15-21
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• 1990

This study focuses the mechanical deformation response predicted by the plasticity model for polycrystalline ice. To describe various deformation characteristics, ice is idealized as a perfectly plastic material using an asymptotic exponential failure criterion. This criterion is suite for describing materials which exhibit brittle deformation at low hydrostatic pressure and ductile deformation at high hydrostatic pressure. The results are compared to those of continuum damage mechanics model. Plasticity model shows good agreement with damage model and experimental results for high confining pressures even at high strain-rates which is usually considered as a brittle condition under uniaxial compression.

• Journal of Ocean Engineering and Technology
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• v.4 no.2
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• pp.165-165
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• 1990

This study focuses the mechanical deformation response predicted by the plasticity model for polycrystalline ice. To describe various deformation characteristics, ice is idealized as a perfectly plastic material using an asymptotic exponential failure criterion. This criterion is suite for describing materials which exhibit brittle deformation at low hydrostatic pressure and ductile deformation at high hydrostatic pressure. The results are compared to those of continuum damage mechanics model. Plasticity model shows good agreement with damage model and experimental results for high confining pressures even at high strain-rates which is usually considered as a brittle condition under uniaxial compression.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.

• The korean journal of orthodontics
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• v.40 no.5
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• pp.294-303
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• 2010

Objective: This study was designed to measure the surface roughness at the slot floor of various ceramic brackets. Methods: One kind of stainless steel bracket ($Succes^{(R)}$), two kinds of monocrystalline brackets (Inspire $Ice^{(R)}$, $Perfect^{(R)}$) and two kinds of polycrystalline brackets (Crystalline $V^{(R)}$, $Invu^{(R)}$) were examined. Atomic force microscopy (AFM) was used to measure the surface roughness of each bracket. Data acquisition and processing were performed using $SPIP^{TM}$. Results: The differences in values of Sa, Sq, and Sz in $Invu^{(R)}$ and Inspire $Ice^{(R)}$ were not statistically different from the control group $Succes^{(R)}$. The values of Sa, Sq, and Sz of $Perfect^{(R)}$ and Crystalline $V^{(R)}$ were greater than those of $Succes^{(R)}$. Differences of all the Sa, Sq, and Sz values between $Perfect^{(R)}$ and Crystalline $V^{(R)}$ were not statistically significant. Conclusions: It is concluded that the slot surfaces of $Succes^{(R)}$, Inspire $Ice^{(R)}$, and $Invu^{(R)}$ were smooth compared to those of Crystalline $V^{(R)}$ and $Perfect^{(R)}$.

• Journal of Technologic Dentistry
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• v.35 no.1
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• pp.19-27
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• 2013

Purpose: The aim of this research was to evaluate the shear bond strength of different zirconia veneering ceramics with and without liner glass materials to yttria partially-stabilized tetragonal zirconia polycrystalline(Y-TZP). Methods: Five co mmercial zirconia veneering ceramics were used in this study, E-Max(EM), Creation ZI(CR), Cercon ceram kiss(CE), Triceram(TR) and Zirkonzahn ICE(ZI). All samples were prepared according to manufacturer's instructions. Experimental industrially manufactured Y-TZP ceramic blocks(diameter: 2.7 mm; height: 13.5 mm) were used in this study. Shear bond strength between zirconia ceramic coping and zirconia veneering ceramics were evaluated by the push-shear bond test. The fracture load data were analyzed using ANOVA and Scheffe's test(${\alpha}$=0.05). The fractured surfaces of zirconia core ceraimc and zirconia veneering ceramics were observed using a scanning electron microscope(SEM). Results: The mean shear bond strengths ranged from 20 MPa ($20.12{\pm}6.34$ MPa) to 66.6 MPa ($66.62{\pm}10.01$ MPa). The Triceram(TRG) showed the highest value and Creation ZI(CR) showed the lowest value. In all groups, Zirconia liner and glass material groups was significantly higher shear bond strength than without liner(P<0.05), with the exception of Cercon ceram kiss(CE)groups. Conclusion: Zirconia bonding materials may have the advantage of improved bond strength between zirconia ceramic core and veneering ceramics.