• Journal of the Korean Ceramic Society
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• v.41 no.1
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• pp.69-75
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• 2004

The degree of the indentation damage and strength degradation for 3Y-TZP ceramics and (Y,Nb)-TZP/$Al_2O_3$ dental implant composites was investigated under the Hertzian cyclic fatigue. Fatigue tests were conducted at contact loads of 500 to 3000 N and up to $10^6$ cycles in exact in vitro environments. At 500 N, no strength degradation and crack generation was observed up to $5{\times}10^5$ contact cycles. Fatigue properties of 3Y-TZP ceramics was superior to (Y,Nb)-TZP/ㅍ composites due to stress relief caused by the phase transformation from tettagonal to monoclinic phase. As contact load increased, the drastic reduction in strength was found when the damage transition from ring to radial crack occurred. The extent of strength degradation was more pronounced in vitro environments probably due to chemical corrosion of artificial saliva through cracks introduced during large numbers of contacts.

• Advances in nano research
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• v.15 no.6
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• pp.495-511
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• 2023

In this research, the impact of micro-silica, nano-silica, and polypropylene fibers on the fracture energy of self-compacting concrete was thoroughly examined. Enhancing the fracture energy is very important to increase the crack propagation resistance. The study focused on evaluating the self-compacting properties of the concrete through various tests, including J-ring, V-funnel, slump flow, and T50 tests. Additionally, the mechanical properties of the concrete, such as compressive and tensile strengths, modulus of elasticity, and fracture parameters were investigated on hardened specimens after 28 days. The results demonstrated that the incorporation of micro-silica and nano-silica not only decreased the rheological aspects of self-compacting concrete but also significantly enhanced its mechanical properties, particularly the compressive strength. On the other hand, the inclusion of polypropylene fibers had a positive impact on fracture parameters, tensile strength, and flexural strength of the specimens. Utilizing the response surface method, the relationship between micro-silica, nano-silica, and fibers was established. The optimal combination for achieving the highest compressive strength was found to be 5% micro-silica, 0.75% nano-silica, and 0.1% fibers. Furthermore, for obtaining the best mixture with superior tensile strength, flexural strength, modulus of elasticity, and fracture energy, the ideal proportion was determined as 5% micro-silica, 0.75% nano-silica, and 0.15% fibers. Compared to the control mixture, the aforementioned parameters showed significant improvements of 26.3%, 30.3%, 34.3%, and 34.3%, respectively. In order to accurately model the tensile cracking of concrete, the authors used softening curves derived from an inverse algorithm proposed by them. This method allowed for a precise and detailed analysis of the concrete under tensile stress. This study explores the effects of micro-silica, nano-silica, and polypropylene fibers on self-compacting concrete and shows their influences on the fracture energy and various mechanical properties of the concrete. The results offer valuable insights for optimizing the concrete mix to achieve desired strength and performance characteristics.

• Land and Housing Review
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• v.7 no.4
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• pp.323-328
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• 2016

There are small box opening for inserting of electric lamp box in the slab of apartment. Around this box opening, we normally use the detailing of WWF or plastic ring strengthening to protect cracks induced by shrinkage. The shrinkage amount of slab box around was measured and analysed in order to consider validity of these strengthening methods and to find out economical alternative. Alternative of strengthening methods are normally used strengthening methods in construction companies, which are WWF strengthening, plastic ring strengthening and no strengthening methods. The shrinkage amount was measured using contact guage at the spot of tip attached around the box on slab of small area unit apartment which have small exclusive area below $59m^2$. Measured data shows that there are no big differences between all the 3 strengthening methods and Measure data range is $-264{\mu}{\varepsilon}{\sim}+216{\mu}{\varepsilon}$. Measured shrinkage is on trend slightly increase till 3~5weeks after removal of forms and then decrease. But amount of shrinkage are very low for all the slabs and there are no probabilities of concrete crack by shrinkage.

• Restorative Dentistry and Endodontics
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• v.13 no.2
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• pp.337-348
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• 1988

The purpose of this study was to examine the fracture strength and characteristics of teeth with MOD cavity preparation. Freshly extracted sound maxillary premolars were cleaned and stored in normal saline solution $37^{\circ}C$ for 72 hours before experiments. The roots of teeth were embedded in a self-curing resin, and the exposed crown were maintained in a vertical position by a modelling wax in a brass ring. The MOD cavities were prepared with No. 57 carbide bur under high speed to a depth of 2.0mm and a width of 2.0mm(Fig.1). All the prepared teeth specimens were divided into 7 groups according to the mode of cavity form and restorative materials (Table 1, 2): Group I, unpreapred, intact teeth as control Group II, prepared cavity without restoration Group III, prepared teeth restored with amalgam Group IV, prepared teeth restored with composite resin (P-10) Group V, prepared teeth with beveled enamel margins restored with composite resin (P-10) Group VI, prepared teeth restored with light-cured composite resin (P-30) Group VII, prepard teeth with beveled enamel margins restored with light-cured composite resin (P-30) After placement of restorations, all of the specimens were stored in water at $37^{\circ}C$ for 72 hours before testing. All of the specimens were tested on the Instron Universal Testing machine (No. 6025) in order to evaluate the strength of fracture. One metal ball 5.0mm in diameter contacting the specimens parallel to the occlusal surface was used to in this study (Fig. 1). The fracture characteristics of the specimens were examined with naked eye and in the scanning electron microscope (JSM-20). The results obtained from this study were as follows: 1. The mean fracture strength was the highest in group VI and that in group II was the lowest. 2. The progress of crack of teeth propagated into the pulp cavity. 3. In case of the group of the restored teeth, the crack occurred to be accompanied with cuspal fracture. 4. The crack of restored teeth was initiated along the pulpo-axial line angle of the cavity.

• Computational Structural Engineering : An International Journal
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• v.1 no.2
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• pp.107-116
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• 2001

The present paper investigates the nonlinear behavior of reinforced concrete shear walls with a crank based on a finite element analysis. The loading type is a horizontal cyclic one such as earthquake loads. Experiments of the shear walls with and without cranks, performed previously to see flow the behavior changes depending on the crank, are compared with the results obtained from the finite element analysis. The finite element analysis is based on an isoparametric degenerated shell formulation. The nonlinear constitutive equations fur concrete are modeled adopting the formulation based on a concept of Ring Typed-Lattice Model. The experiments indicate that the shear walls with a crank have low stiffness and relatively low carrying capacity compared with an ordinary plane shear wall without cranks and that they are more ductile, and the tendency is a1so confirmed based on the finite element analysis. Moreover, a good agreement between the experiments and analyses is obtained, accordingly, it is confined that the present numerical analysis scheme based on the Lattice Model is a powerful one to evaluate the behavior of reinforced concrete shear walls with cranks and without cranks.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.9
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• pp.93-99
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• 2020

Recently, as the weight reduction of vehicles has been actively progressed, parts developed using aluminum 60XX series from existing steel materials are increasing. In this paper, the bushing used for the front frame rail, which is one of the parts for fixing engines and other parts in automobiles, was changed to an aluminum material of the Al60XX series, and it was intended to be produced by applying of cold forging method. The bushing is a part that secures the engine frame, and in order to produce it by cold forging, the molding limit is predicted through process design, and a multi-stage process is designed through finite element analysis. In addition, in order to verify the feasibility of the designed forging process, the limits of the multi-step process were verified based on the Cockcroft Latham theory, and the crack and overlap of the actual forging work were predicted and improved.

• Journal of Biosystems Engineering
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• v.27 no.4
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• pp.293-300
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• 2002

Surface crack detection is an important aspect in the quality control process of egg markets. The acoustic vibration of an egg could be used as a critical factor in evaluating the eggshell quality. The mode shape indicates the egg vibration behavior at different locations with respect to the input impulse and provides important information for the optimum sensor location to obtain the desired acoustic measurements. Theoretical analysis and experimental measurements were conducted to determine the acoustic vibration modes in eggs. The resonant fiequencies of the first and second resonance mode of intact eggs were found to be distributed between 2kHz and 7kHz range. The measured mode shapes of an egg were similar to theoretical shapes of homogeneous, elastic spheres. An elliptical deformation at the equator ring of the egg was observed. The frequency peak of this mode was dominantly present in the frequency spectrum of an intact egg impacted at its sharp position. The mode shapes related to the first resonant frequency of an egg shelved that the optimum location for the measuring sensor was the 180 degrees position. A optimum location for the egg support was found to be the 90 degrees position having the smallest vibration magnitude.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3847-3855
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• 1996

In order to study the relationship between static and cynamic behaviors of silion caride, both quasi-static indentaiton and impact experiments of spherical particle have been conducted. The difference inmaterial behavior when using the two mehtods suggests a loading rate difference in the damate pattrern and fracture strength of silicon carbide. This investigation showed some difference in damage pattern according to particla property, especially inthe case of particle impact. There was no differences in deformation behaviors according to the loading rate when the crater profiles were compared with each other at the same contact radius. From the result of residual strength evaluation, it was found that the strength degradation began at the initiation of ring crack and its behavior was colsely related to morphologies of the damage developed which was also dependent upon the extent of deformation atthe loaidng point. In the case of static indentation, there didnot exist the particle property effects onthe strength degradation behavior.

• Journal of the Korean Wood Science and Technology
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• v.22 no.2
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• pp.61-70
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• 1994

This study was executed to find the applicability of press drying of tree disk by investigating the shrinkage and drying defect and to form appropriate model by comparing the actual moisture content(MC) and internal temperature in respect of drying time with calculated values based computer simulation to which was applied finite difference method. In press drying disk, heating period, constant drying rate period maintained plateau temperature at 100$^{\circ}C$ and falling drying rate period were significantly distinguished. Actual MC and internal temperature were analogous to those calculated at comparing points. Heat transfer model formed by Fourier's law using specific heat of moist wood and conduction coefficient considering fractional volume of each element of wood cell wall, bound water, free water and air showed applicability as basic data to developing heat expansion, shrinkage and drying stress during press drying. Also mass transfer model formed by Fick's diffusion law using water vapor diffusion coefficient showed applicability. Longitudinal shrinkage was developed by pressure of hot press and tangential shrinkage was restrained by hygrothermal recovery. The heart check, surface check and ring failure were occurred differently in species, but V-shaped crack didn't develop.

• Corrosion Science and Technology
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• v.20 no.4
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• pp.175-182
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• 2021

Magnesium alloy is limited in the industrial field because its standard electrode potential is -2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 ℃. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 ℃ in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.