• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.8-18
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• 2010

This study aimed at investigating quasi-static and dynamic torsional deformation behavior of three API X70 and X80 linepipe steels. Quasi-static and dynamic torsional tests were conducted on these steels. having different grain sizes and volume fractions of acicular ferrite and polygonal ferrite, using a torsional Kolsky bar. The test data were then compared via microstructures and adiabatic shear band formation,. The dynamic torsional test results indicated that the steels rolled in the single phase region had higher maximum shear stress than the steel rolled in the two phase region, because the microstructures of the steel rolled in the single phase region were composed mainly of acicular ferrites. In the X80 steel rolled in the single phase region, the increased dynamic torsional properties could be explained by a decrease in the overall effective grain size due to the presence of acicular ferrite having smaller effective grain size. The possibility of adiabatic shear band formation was analyzed from the energy required for void initiation and variation in effective grain size.

• Journal of Adhesion and Interface
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• v.23 no.3
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• pp.87-93
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• 2022

To analyze the interfacial property between the fiber and the matrix, work of adhesion was used generally that was calculated by surface energies. In this paper, it was determined what types of contact angle measurement methods were more accurate between static and dynamic contact angle measurements. 4 types of glass fiber and epoxy resin were used each other to measure the contact angle. The contact angle was measured using two types, static and dynamic contact angle methods, and work of adhesion, W_a was calculated to compare interfacial properties. The interfacial property was evaluated using microdroplet pull-out test. Generally, the interfacial property was proportional to work of adhesion. In the case of static contact angle, however, work of adhesion was not consistent with interfacial property. It is because that dynamic contact angle measurement comparing to static contact angle could delete the error due to microdroplet size to minimize the surface area as well as the meniscus measuring error.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.2
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• pp.116-116
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• 1996

This paper is concerned with a method for calibrating five-hole probes of both angle-tube and prismatic geometries to measure local total and static pressures and the magnitude and direction of the mean velocity vector. Descriptions of the calibration technique, the typical calibration data, and an accompanying discussion of the interpolation procedure are included. The flow properties are determined explicitly from measured probe pressures using calibration data. Flow angles are obtained within the deviation angle of 1.0 degree and dynamic pressures within 0.03 with 95% certainty. The variations in the calibration data due to Reynolds number are also discussed. For the range of Reynolds number employed, no effect was detected on the pitch, yaw and total pressure coefficients. However, the static pressure coefficient showed change to cause minor variations in the magnitude of the calculated velocity vector. To account for these variations, average correction factors need to be incorporated into the static pressure coefficient.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.2
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• pp.48-56
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• 1996

This paper is concerned with a method for calibrating five-hole probes of both angle-tube and prismatic geometries to measure local total and static pressures and the magnitude and direction of the mean velocity vector. Descriptions of the calibration technique, the typical calibration data, and an accompanying discussion of the interpolation procedure are included. The flow properties are determined explicitly from measured probe pressures using calibration data. Flow angles are obtained within the deviation angle of 1.0 degree and dynamic pressures within 0.03 with 95% certainty. The variations in the calibration data due to Reynolds number are also discussed. For the range of Reynolds number employed, no effect was detected on the pitch, yaw abd total pressure coefficients. However, the static pressure coefficient showed change to cause minor variations in the magnitude of the calculated velocity vector. To account for these variations, average correction factors need to be incorporated into the static pressure coefficient.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.4
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• pp.118-125
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• 2009

Bumper is designed to protect the automotive frame without damage at low velocity. Expanded polypropylene (EPP) foam is used in the bumper as an energy absorbing material. In order to exactly predict the energy absorbing performance of the foam material under impact loading condition, it is important to use high strain rate material properties. In this study, a new apparatus for dynamic compression tests was developed to investigate the high strain rate behavior of EPP foams. Three kinds of EPP foams which have different expansion ratios were tested to investigate the quasi-static and dynamic compression behavior. Quasi-static compressions were performed at low strain rates of 0.001/s, 0.1/s and 1/s. The dynamic compressions were carried out at high strain rates of 50/s and 100/s with the developed apparatus. It was observed that the EPP foam has significant strain rate effect as compared to quasi-static behavior.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.297-316
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• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• Transactions of Materials Processing
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• v.8 no.5
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• pp.471-481
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• 1999

The properties of deformed products are generally dependent upon the distribution of microstureture. It is, therefore, necessary to make the distribution of microstureture uniform in order to achieve the best balance of properties in the final product. This is often a demanding task, even for conventional materials. It is become essential to achieving mechanical integrity and a desired combination of microstructure and properties. The objective mechanical integrity and a desired combination of microsttucture and properties. The objective of this study is to design the optimal die profile which can yield more uniform microstructure in hot extruded product. The microstructure evolution, such as dynamic and static recrystallization as well as grain growth, is investigated using the program com-bined with yada and Senuma's empirical equations and rigid-thermoviscoplastic finite element method. The die profile of hot extrusion is represented by Bezier-curve to define all available profile. In order to obtain the optimal die profile which yields uniform microstructure in the product the FPS(Flexible Polyhedron Search) method is applied to the present study. To validate the result of present study the experimental hot extrusion is performed and the result is compared with that of simulation.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1996.06c
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• pp.283-292
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• 1996

This study was performed to determine the physical properties of rice hull and straw which could be used for an optimum design and operation of the handling facilities for these rice crop by-products. The properties measured were kinetic friction coefficient , bulk density, and dynamic and static angle of repose. Rice hulls with moisture content of 13% and 21% were used throughout the test while rice straws of 10% and 16% moisture were chopped into 10mm length and used for the test. Friction coefficient was calculated from the horizontal traction forces measurement when a container holding the mass of rice hull and straw was pulled over mild steel. PVC, stainless steel, and galvanized steel surface by a universal testing machine. Bulk density was measured by an apparatus consisting of filling fundel and a receiving vessel. Dynamic angle of repose which is the angle at which the material will stand when piled was calculated from the photos of bulk samples after they were flowed by gravity and accumulated on a circular surface. Static angle of repose which is the angle between the horizontal and the sloping side of the material left in the container when discharging was also measured in the similar way. Results and conclusions from this study are summarized as follows . 1. Kinetic friction coefficient of both rice hull and straw were in the range of 0.26 -0.52 and increased with the moisture content. The magnitude of friction increased in the order of galvanized steel, stainless steel, PVC ,and mild steel. 2. Bulk densities of rice hull decreased while those of rice straw increased with moisture content increase . Average bulk densities of rice hull and straw were 96.8 and 74.7kg/㎥, respectively. 3. Average dynamic angle of repose for rice straw was 32.6$^{\circ}$ and those for 13% and 21% moisture rice hull were 38.9$^{\circ}$ and 44.9$^{\circ}$ , respectively. 4. Static angles of repose for both rice hull and straw showed increase with the moisture content. The values were 75.2\ulcorner and 80.2$^{\circ}$ for 13% and 21% moisture rice hull, respectively. Rice straws having 10% and 16% moisture content showed 87.3% and 89.2$^{\circ}$ static angle of repose, respectively.

• Nuclear Engineering and Technology
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• v.52 no.8
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• pp.1714-1723
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• 2020

This study aims at characterizing the rheological properties of uranium oxide powders for nuclear fuel pellets manufacturing. The flowability of these powders must be compatible with a reproducible filling of press molds. The particle size distribution is known to have an impact on the rheological properties and fine particles (<100 ㎛) are suspected to have a detrimental effect. In this study, the impact of the particle size distribution on the rheological properties of UO₂ powders was quantified, focusing on the influence of fine particles. Two complementary approaches were used. The first approach involved characterizing the powder in a static state: density, compressibility and shear test measurements were used to understand the behavior of the powder when it is transitioned from a static to a dynamic state (i.e., incipient flow conditions). The second approach involved characterizing the behavior of the powder in a dynamic state. Two zones, corresponding to two characteristic behaviors, were demonstrated for both types of measurements. The obtained results showed the amount of fines should be kept below 10 % wt to ensure a robust mold filling operation (i.e., constant mass and production rate).

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.15 no.11 s.104
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• pp.1295-1302
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• 2005

This paper shows experimental evaluation results of the nano-positioning planar scanner used in the scanning probe microscope. The planar scanner is composed of flexure guides, piezoelectric actuators and feedback sensors as like explained in detail in Ref. (5). First, the fabrication methods were explained. Second, as the static Properties of the Planar scanner. we evaluated the maximum travel range & crosstalk. Also, we presented the correcting method for crosstalk using electric circuits finally. as the dynamic properties of the planar scanner, we evaluated the first resonant frequency. Also, we presented the actual AFM(atomic force microscope) imaging results with up to 2Hz imaging scan rate. Experimental results show that properties of the proposed planar scanner are well enough to be used in SPM applications like AFM.