• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.1
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• pp.71-80
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• 1990

The fracture characteristics of concrete under various rates of loading are investigated. The static and dynamic fracture energies of concrete are determined and the size-dependency of fracture energy is clarified from the present study. To this end, a series of experiments were conducted. The maximum failure loads, fracture energies and nominal failure stresses were calculated from those test results. It is found that the fracture energies are increased with the increase of loading rate. The fracture energy values were also greatly influenced with the size of the specimen. The size-dependent prediction eguations for the static and dynamic fracture energies of concrete are proposed in the present study. The present paper provides useful data for the dynamic fracture analysis of concrete structures.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.9
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• pp.793-798
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• 2015

This study investigates the effects of the size of copper sheets on the plastic deformation behavior in a microscale deep drawing process. Tensile tests are conducted on the copper sheets to study the flow stress of the materials with different grain sizes before carrying out the microscale deep drawing experiments. After the tensile tests, a novel desktop-sized microscale deep drawing system is used to perform the microscale deep drawing process. A series of microscale deep drawing experiments are subsequently performed, and the experimental results indicate that an increase in the grain size results in the reduction of the deformation load of the copper sheets due to the effects of the surface grain. The results also show that the blank holder gap improves both the formability of copper sheets and the material flow.

• Steel and Composite Structures
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• v.28 no.1
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• pp.99-110
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• 2018

In this paper, a new size-dependent quasi-3D plate theory is presented for wave dispersion analysis of functionally graded nanoplates while resting on an elastic foundation and under the hygrothermaal environment. This quasi-3D plate theory considers both thickness stretching influences and shear deformation with the variations of displacements in the thickness direction as a parabolic function. Moreover, the stress-free boundary conditions on both sides of the plate are satisfied without using a shear correction factor. This theory includes five independent unknowns with results in only five governing equations. Size effects are obtained via a higher-order nonlocal strain gradient theory of elasticity. A variational approach is adopted to owning the governing equations employing Hamilton's principle. Solving analytically via Fourier series, these equations gives wave frequencies and phase velocities as a function of wave numbers. The validity of the present results is examined by comparing them with those of the known data in the literature. Parametric studies are conducted for material composition, size dependency, two parametric elastic foundation, temperature and moisture differences, and wave number. Some conclusions are drawn from the parametric studies with respect to the wave characteristics.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.59-67
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• 1999

The mass concrete structures are generally constructed in an incremental manner by deviding the whole structures by a series of many blocks. The temperature and stress distributions of any specific block are continuously affected by the blocks placed before and after the specific block. For an accurate analysis of mass concrete structures, the sequence of all the blocks must be accordingly considered including the change of material properties with time for those blocks considered. The purpose of this study is to propose a realistic analysis method which can take into account not only the influence of the sequence, time interval and size of concrete block placement on the temperatures and stresses, but also the change of material properties with time. It is seen from this study that the conventional simplified analysis, which neglects material property changes of some blocks with time and does not consider the effect of adjacent blocks in the analysis, may yield large discrepancies in the temperature and stress distributions of mass concrete structures. This study gives a method to choose the minimum number of blocks required to obtain reasonably accurate results in analysis. The study provides a realistic method which can determine the appropriate size and time interval of block placement, and can be efficiently used in the design and construction of mass concrete structures.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.369-372
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• 2000

ZnO varistor is studied to sintering condition and mixing condition for the improvement to non linear of electrical characteristics. In this paper, ZnO varistor, ZnO-Bi$_2$O$_3$-Y$_2$O$_3$-MnO-Cr$_2$O$_3$-Sb$_2$O$_3$series, is fabricated with Sb$_2$O$_3$mol ratio(0.5~4[mol%]) and sintered at 1250[$^{\circ}C$] for 2 hours. The grain size to Sb$_2$O$_3$moi ratio was measured by fractal mathematics. The ZnO varistors that Sb$_2$O$_3$mot ratio is 1[mol%] were shown small grain size because of spinel phase. The fractal dimension were increased with increasing of Sb$_2$O$_3$mo ratios. The capacitance of ZnO varistors with increasing of Sb$_2$O$_3$additive in voltage-capacitance characteristics was decreased by small grain size.

• Applied Chemistry for Engineering
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• v.9 no.5
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• pp.648-653
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• 1998

This study examines the effects of cell size and structure on the oil adsorption by polyurethane (PU) foam. A series of oil-adsorptive PU foam has been prepared, using various molecular weight of polyether polyol (GP-1000, GP-3000, GP-4000, GP-5000), together with TDI-80, water and additives. It was found that the cell size of PU foam decreased with increasing the agitation speed and surfactant content. Oil-adsotption of PU foam increased over 2000% with the increase of molecular weight of polyol and with the decrease of cell size. Increase in the surfactant content and the viscosity of adsorbed oil also give a remarkable decrease in oil adsorption.

• The Journal of Korean Obstetrics and Gynecology
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• v.28 no.1
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• pp.147-157
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• 2015

Objectives: We report two cases that have an effective result with Korean traditional medical treatment to two patients who have uterine fibroids, using transabdominal ultrasonography for checking the size of uterine fibroids. Methods: A 44-year-old patient and a 43-year-old patient were treated with an herbal medicine, acupuncture and cupping therapy. We followed up the symptoms and the size of uterine fibroids. Results: The 44-year-old patient was asymptomatic, her size of the uterine fibroid was reduced for 6 months. Also, the 43-year-old patient experienced that the symptoms such as urinary frequency, ovulation pain, heavy bleeding were improved and the size of the uterine fibroid was reduced. Conclusions: This results suggest that Korean traditional medical treatment if effective for both asymptomatic and symptomatic uterine fibroids and ultrasonography is useful for checking the effect of Korean traditional medical treatment. Further case series and studies are warranted.

• Computers and Concrete
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• v.26 no.6
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• pp.587-593
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• 2020

In this study, bond behavior of ordinary concrete and rebars with different diameters and development length was investigated by using Hinged Beam Test (HBT) and Eccentric Pull-Out Test (EPT) comparatively. For this purpose, three different rebar size and development length depending on rebar diameter were chosen as variables. Three specimens were produced for each series of specimens and totally 54 specimens were tested. At the end of the tests it was observed that obtained results for both tests were quite similar. On the other hand, increased bar size, especially for the specimen with 14 mm bar size and 14 development length (lb), caused shear failure of test specimens. This situation infers that when bigger bar size and lb are used in such test, dimensions of test specimens should be chosen bigger and stirrups should be used for producing of test specimens to obtain more adequate result by preventing shear failure. Also, a nonlinear regression analysis was employed between HBT and EPT results. There was a high correlation between the EPT values, lb, rebar diameters and estimated theoretical HBT. In addition, at the end of the study an equation was suggested to estimate bond strength for HBT by using EPT results.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.19-26
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• 2022

In droplet microfluidics, precise droplet manipulation is required in numerous applications. This study presents ultrasonic surface acoustic wave (USAW)-based microfluidic device for label-free droplet separation based on size. The proposed device is composed of a slanted-finger interdigital transducer on a piezoelectric substrate and a polydimethylsiloxane microchannel placed on the substrate. The microchannel is aligned in the cross-type configuration where the USAWs propagate in a perpendicular direction to the flow in the microchannel. When droplets are exposed to an acoustic field, they experience the USAW-induced acoustic radiation force (ARF), whose magnitude varies depending on the droplet size. We modeled the USAW-induced ARF based on ray acoustics and conducted a series of experiments to separate different-sized droplets. We found that the experimental results were in good agreement with the theoretical estimation. We believe that the proposed method will serve as a promising tool for size-based droplet separation in a label-free manner.

• Geomechanics and Engineering
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• v.35 no.5
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• pp.475-486
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• 2023

Ballast particles have an irregular shape and are discrete in nature. Due to the discrete nature of ballast, it exhibits complex mechanical behaviour under loading conditions. The discrete element method (DEM) can model the behaviour of discrete particles under a multitude of loading conditions. DEM is used in this paper to simulate a series of three-dimensional direct shear tests in order to investigate the shear behaviour of railway ballast and its interaction at the microscopic level. Particle flow code in three dimension (PFC3D) models the irregular shape of ballast particles as clump particles. To investigate the influence of particle size distribution (PSD), real PSD of Indian railway ballast specification IRS:GE:1:2004, China high-speed rail (HSR) and French rail specifications are generated. PFC3D built-in linear contact model is used to simulate the interaction of ballast particles under various normal stresses, shearing rate and shear box sizes. The results indicate how shear resistance and volumetric changes in ballast assembly are affected by normal stress, shearing rate, PSD and shear box size. In addition to macroscopic behaviour, DEM represents the microscopic behaviour of ballast particles in the form of particle displacement at different stages of the shearing process.