• Geotechnical Engineering
• /
• v.11 no.3
• /
• pp.43-54
• /
• 1995

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated soil and to confirm the application'of the model, which is composed of the elastic and plastic part in consideration of the matric suction and the net mean stress. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. The application of the model to silty sands is confirmed by the comparison between test and predicted results. During drying -wetting and loading -unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. Predicted deviator stresses are well agreed with test results in shearing process. Overall acceptable predictions are reproduced in high confining pressure. Usefulness of the model is confirmed for the unsaturated soil except volumetric strain, which is not well agreed with the test results due to deficiency of dilatancy of the model in low confining pressure. It is, therefore. recommended to study the behavior of dilatancy for an unsaturated soil.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.37 no.1
• /
• pp.81-89
• /
• 1995

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated Soil and to confirm the application of the model, which is composed of the elastic and plastic part in consideration of the matric suction and the net mean stress. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. And the application of the model to silty sands is con- firmed by the comparison between test and predicted results. During drying-wetting and loading-unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. And predicted deviator stresses are well agreed with test results in shearing process. Overall acceptable predictions are reproduced in high confining pressure. Usefulness of the model is confirmed for the unsat- urated soil except volumetric strain, which is not well agreed with the test results due to deficiency of dilatancy of the model in low confining pressure. It is, therefore, recom- mended to study the behavior of dilatancy for an unsaturated soil.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.38 no.3
• /
• pp.101-110
• /
• 1996

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated clayey soil and to confirm the application of the model. To this end a series of suction controlled isotropic and triaxial compression tests are conducted on clayey soils. Matric suction is controlled by the axis translation technique using high air entry ceramic disk. Total volume change, air and water volume changes are measured by the device made for the experiment. The specimens are compacted by dynamic compaction using a half of Proctor compaction energy with the water contents of 5% drier than the optimum moisture contents. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. And the application of the model to clayey soils is confirmed by the comparison between test and predicted results. During drying-wetting and loading-unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. And predicted deviator stresses are well agreed with the test results in shearing process, but volumetric strain is not well agreed with the test results in high suctions.

• Magazine of the Korea Concrete Institute
• /
• v.9 no.3
• /
• pp.189-197
• /
• 1997

This paper describes an experimental study on the seawater resistance of steel fiber reinforced concrete. The test methods adopted for this study are divided into long-term immersion test and acceleration test by wetting and drying. Tests were carried out to evaluate the procedures which were measured for nine months about reduction in dynamic modulus, length change and compressive strength. Resistance indicators are the water-cement ratio, the content of steel fiber, the content of fly ash, the immersion water(artificial seawater or freshwater) and the types of curing. The seawater resistance of the appropriate additions of steel fiber and fly ash have apparently increased.

• Journal of the Korean Vacuum Society
• /
• v.8 no.3B
• /
• pp.262-268
• /
• 1999

Polycarbonate (PC) and Polymethylmethacrylate (PMMA) surface was modified by ion assisted reaction (IAR) technique to obtain the hydrophilic functional groups and improve the wettability. In conditions of ion assisted reaction, ion beam energy was changed from 500 to 1500eV, and ion dose and oxygen gas blown rate were fixed $1\times10^{16}$ ions/$\textrm{cm}^2$ and 4ml/min, respectively. Wetting angle of water on PC and PMMA surface modified by $Ar^+$ ion without blowing oxygen at 4ml/mon showed $5^{\circ}$ and $10^{\circ}$. Changes of wetting angle with oxygen gas and $Ar^+$ ion irradiation were explained by considering formation of hydrophilic group due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas. X-ray photoelectron spectroscopy analysis shows that hydrophilic groups such as -C-O, -(C=O)- and -(C=O)-O- are formed on the surface of polymer by chemical interaction. The polymer surface modification using ion assisted reaction only changed the surface physical properties and sept the bulk properties. In comparison with other modification methods, the surface modification by IAR treatment was chemically stable and enhanced the adhesion between metal and polymer surface. The applications of various kinds of polymer surface modification methods, metal and polymer surface. The applications of various kinds of polymer surface modification could be appled to the new materials about hydrophilic surface properties by IAR treatment. The adhesion between metal film and polymer measured by Scotch tape test whether the hydrophilic surfaces could improve the adhesion strength or not.

• Journal of the Korean Geotechnical Society
• /
• v.19 no.1
• /
• pp.41-49
• /
• 2003

Rainfall-induced landslides in a weathered granite soil slope usually happen on shallow slip surfaces above the groundwater table. The pore-water pressure of soil above the groundwater table is usually negative. This negative pore-water pressure (or matric suction) has been found to make a large contribution to the slope stability. Therefore, the variation of in-situ matric suction profiles with time elapse in a soil slope should be understood. In this study, a field measurement program was carried out from June to August, 2001 in order to monitor in-situ matric suctions and volumetric water contents in a weathered granite soil slope. Finite-element transient seepage analyses are also conducted using SEEP/W. The influence of climatic conditions on the variation of in-situ matric suctions could be found to decrease rapidly with the change of depth. It could be found that decrement of matric suction induced by precipitation is affected not only by the amount and duration of rainfalls but also by the initial matric suction just prior to rainstorms. The soil-water characteristic from the field monitoring tends toward the wetting path of SWCC obtained from the laboratory test.

• Restorative Dentistry and Endodontics
• /
• v.40 no.1
• /
• pp.68-74
• /
• 2015

Objectives: This study examined the effects of additional acid etching on the dentin bond strength of one-step self-etch adhesives with different compositions and pH. The effect of ethanol wetting on etched dentin bond strength of self-etch adhesives was also evaluated. Materials and Methods: Forty-two human permanent molars were classified into 21 groups according to the adhesive types (Clearfil SE Bond [SE, control]; G-aenial Bond [GB]; Xeno V [XV]; Beauti Bond [BB]; Adper Easy Bond [AE]; Single Bond Universal [SU]; All Bond Universal [AU]), and the dentin conditioning methods. Composite resins were placed on the dentin surfaces, and the teeth were sectioned. The microtensile bond strength was measured, and the failure mode of the fractured specimens was examined. The data were analyzed statistically using two-way ANOVA and Duncan's post hoc test. Results: In GB, XV and SE ($pH{\leq}2$), the bond strength was decreased significantly when the dentin was etched (p < 0.05). In BB, AE and SU (pH 2.4 - 2.7), additional etching did not affect the bond strength (p > 0.05). In AU (pH = 3.2), additional etching increased the bond strength significantly (p < 0.05). When adhesives were applied to the acid etched dentin with ethanol-wet bonding, the bond strength was significantly higher than that of the no ethanol-wet bonding groups, and the incidence of cohesive failure was increased. Conclusions: The effect of additional acid etching on the dentin bond strength was influenced by the pH of one-step self-etch adhesives. Ethanol wetting on etched dentin could create a stronger bonding performance of one-step self-etch adhesives for acid etched dentin.

• Journal of the Microelectronics and Packaging Society
• /
• v.28 no.2
• /
• pp.45-50
• /
• 2021

As the difficulty of flip chip products increases, there is a growing interest in the material of flux, which is safe from the solder wetting and reliability. In the case of no clean flux, there is merit in terms of process efficiency because there is no cleaning process. But Cu migration and delamination can be occurred if the residue remains after the reflow process. In this study, major element materials, solvent and activator, are changed and confirmed effect of non-wet and reliability in the package environment. Stability of materials were secured through storage stability evaluation, and we found out non-wet zero materials through the application of two types of solvent and activator with different boiling point and the increase of activator content. After reliability test, no delamination was found in the plane analysis, which secured the final composition of low residue flux.

• Composites Research
• /
• v.35 no.2
• /
• pp.80-85
• /
• 2022

This work presents an experiment study to evaluate the nanoparticle adhesion and surface hydrophobicity characteristics of Teflon-polyurethane top coat depending on the number of multi-wall carbon nanotube (MWCNT) coatings, which is a carbon-based hydrophobic particle. In order to measure the adhesion between the nanoparticles and the top coat, adhesion pull-off test was performed with different MWCNT oxidation times. Static contact angle and roughness measurements were carried out to characterize the surface hydrophobic behavior. Through the roughness evaluation, it was confirmed that the carbon nanotubes were wetted in the Teflon-polyurethane top coat, and the degree carbon nanotube wetting was confirmed through a USB-microscope. As a result, it was found that the larger the degree of wetting, the better the adhesion. From the experimental results, as the hydrophobicity of Teflon-polyurethane increased, the adhesive propertydecreased with the number of coatings. It was possible to improve the adhesive force and determine the number of coatings of carbon nanotubes with optimized hydrophobicity.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.2
• /
• pp.82-86
• /
• 2011

Lightweight aggregate which is composed of sintered polycrystalline materials usually has a certain portion of pores inside of it. Because of such a structural characteristics, it tends to that movement of water in aggregate shows an abnormal behavior against the change of outside environment. In general, water movement behavior is controlled by porosity, distribution of pore size; however, dense surface layer will also affect water movement behavior in case of artificially sintered aggregates. Factors affecting water movement behavior in the aggregate are pore distribution, pore shape, pre-wetting method, etc. In this study, absorption characteristics of aggregate under the pressure and absorption rate according to water dipping time are analyzed for the basis of pressure pumping of lightweight concrete. Two kinds of aggregates were used for the test: one is made by 'L' company in Germany and the other is of our own made at the pilot plant in Kyonggi University. Absorption rate of aggregate is measured according to water dipping time, vacuum pressure, and quenching condition. Absorption rate of aggregate with $300^{\circ}C$ quenching is higher than that of aggregate with 24 hr water dipping. Generally the more vacuum the higher water absorption rate. Water absorption rate of 'L' aggregate under -300 mmHg is 54 % higher than that of aggregate with 24 hr water dipping; however, only 2 % increase in water absorption was measured for the K622 and K73 which were of our own.