• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.1
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• pp.62-66
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• 2015

In this paper, a fretting testing machine is developed using ball-on-flat test apparatus. Precise micro-slip motion is produced by a linear stage. A relative displacement between a ball and a flat specimen is measured with a laser displacement sensor. Dry friction tests are conducted with AISI 52100 steel balls and cold-rolled high strength steel plates at room temperature and ambient humidity. The evolution of the kinetic friction coefficient is determined. Comparison between measured friction coefficients and those found in the literature is then carried out. Fretting tests with an electro-deposited coating are employed at an amplitude of 0.05 mm. Slip regime is identified with slip ratio. It is demonstrated that a developed testing machine allows determining the friction coefficient under fretting condition.

• Transactions of Materials Processing
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• v.5 no.2
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• pp.97-104
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• 1996

It is very important to obtain the knowledge of loads and flow patterns in most processes because these information are the fundamental data of die design and process design. The objective of present study is to investigate loads and metal flow patterns for various process conditions in flat die extrusion of square-bars from circular billets. For analyzing the metal flow patterns of the billets photo etching is used on sections of split specimen. From this method metal flow patterns are analyzed for various area reductions friction factors and punch stroke through the process from initial-stage to final-stage. Experiments are carried out with hard solder billets at room temperature.

• International Journal of Concrete Structures and Materials
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• v.6 no.1
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• pp.19-29
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• 2012

In this study, three isolated interior flat slab-column connections that include three types of shear reinforcement details; stirrup, shear stud and shear band were tested under reversed cyclic lateral loading to observe the capacity of slab-column connections. These reinforced joints are 2/3 scale miniatures designed to have identical punching capacities. These experiments showed that the flexural failure mode appears in most specimens while the maximum unbalanced moment and energy absorbing capacity increases effectively, with the exception of an unreinforced standard specimen. Finally, the results of the experiments, as wel l as those of experiments previously carried out by researchers, are applied to the eccentricity shear stress model presented in ACI 318-08. The failure mode is therefore defined in this study by considering the upper limits for punching shear and unbalanced moment. In addition, an intensity factor is proposed for effective widths of slabs that carry an unbalanced moment delivered by bending.

• Journal of the Korean Wood Science and Technology
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• v.33 no.5 s.133
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• pp.13-20
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• 2005

This paper deals with flexural vibration techniques as a means of predicting bending strength properties for quarter-sawn and flat-sawn planes of red pine containing knots. Dynamic modulus of elasticity $(MOE_d)$ was calculated from resonance frequency obtained from the flexural vibration induced by a magnetic driver in quarter-sawn and flat-sawn planes of red pine containing knots. The dynamic MOE were well correlated to bending strength properties. Their correlation coefficients ranged from 0.866 to 0.800 for the regression between dynamic MOE and static bending MOE or MOR. The difference of the values between quarter-sawn and flat-sawn was very small. These values were higher than correlation between percentage of total knot diameter to total width of red pine specimen $(K_T(%))$ as well as $K_O(%)$ base upon ASTM D 3737 and static bending strength properties (correlation coefficient r = 0.448~0.704), and were similar to those between static bending MOE and bending MOR (r = 0.850). These results indicate that dynamic MOE obtained from resonance frequency induced by flexural vibration of magnetic driver is able to effectively use for predicting of static bending strength of red pine containing knots as well as static MOE.

• Polymer(Korea)
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• v.36 no.5
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• pp.555-563
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• 2012

Warpage of injection molded product is caused by non-uniform shrinkage during shaping operation and relaxation of residual stress. Robust part design and glass fiber reinforced reins have been adopted to prevent warpage of part. Warpages for part designs have been investigated in this study according to the injection molding conditions. Part design contains flat specimen and two different rib designs in the flat part. Resins used in this study were glass fiber reinforced amorphous plastics, PC and ABS. Different rib designs showed significant differences of warpages in the parts. Various warpages have been observed in the three regions of the part, near gate region, opposite region to the gate, and flow direction region. Results of computer simulation revealed that the warpages were strongly related to glass fiber orientation. Flat specimen showed the smallest warpage and the specimen with ribs to the flow direction showed a high resistance to warpage. Warpage highly depended upon part design rather than molding condition. It was concluded that the rib design and selection of gate location in injection molding would be the most important factors for the control of warpage since those are directly related to the fiber orientation during molding.

• Journal of the Korean Society for Nondestructive Testing
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• v.6 no.1
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• pp.23-30
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• 1986

The optimumultrasonic test conditions for the thin carbon fiber reinforced plastic (CFRP) sheet were determined for the immersed reflector plate method. The effects of the water distance, the surface conditions of the specimen and transducer characteristics were studied. For a reliable test the water distance between the transducer and the front surface of the specimen should be determined when the beam profile of the transducer appears in the bell-shape. The detectability of the defect was improved as the effective beam width of the ultrasonic transducer became narrow. The transducer should be properly chosen considering to the surface condition of the test material as well as the size and type of the defect to be detected. It was possible to detect the flat bottom hole whose diameter is as small as about 500 micrometer.

• Applied Microscopy
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• v.46 no.2
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• pp.110-115
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• 2016

Transmission electron microscopy (TEM) is a powerful tool for analyzing a broad range of materials and provides localized information about the microstructure. However, the analysis results are strongly influenced by the quality of the thin foil specimen. Sample preparation for TEM analysis requires considerable skill, especially when the area of interest is small or the material of interest is difficult to thin because of its high hardness and its mechanical instability when thinned. This article selectively reviews recent advances in TEM sample preparation techniques using a tripod polisher. In particular, it introduces two typical types (fl at type and wedge type) of TEM sample preparation and the benefits and drawbacks of each method; finally, a method of making better samples for TEM analysis is suggested.

• Journal of Powder Materials
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• v.9 no.4
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• pp.218-226
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• 2002

The purpose of the present study is to investigate the influence of thermal debinding and sintering conditions on the sintering behavior and mechanical properties of PIMed 316L stainless steel. The water atomized powders were mixed with multi-component wax-base binder system, injection molded into flat tensile specimens. Binder was removed by solvent immersion method followed by thermal debinding, which was carried out in air and hydrogen atmospheres. Sintering was done in hydrogen for 1 hour at temperatures ranging from 1000℃ to 1350℃ The weight loss, residual carbon and oxygen contents were monitored at each stage of debinding and sintering processes. Tensile properties of the sintered specimen varied depending on the densification and the characteristics of the grain boundaries, which includes the pore morphology and residual oxides at the boundaries. The sinter density, tensile strength (UTS), and elongation to fracture of the optimized specimen were 95%, 540 MPa, and 53%, respectively.

• Journal of Ocean Engineering and Technology
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• v.21 no.1 s.74
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• pp.40-44
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• 2007

This paper presents the experimental results on slamming phenomenon. The air pressure cylinder was used to ensure repeatability of the impact. The results showed that the adopted experimental technique was excellent in terms of repeatability, compared to that of the free drop tests. The pressure time histories, magnitude of peak pressure and the behavior of jetspray were obtained. The flat specimen was tested for various incident angles. To estimate the incident speed of the specimen, a high-speed camera was used. The high-speed camera was also a useful tool in understanding the behavior.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.45-50
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• 2001

This paper presents application of neutron diffraction technique to the measurement of residual stresses in the T-type 20 m thick welded stainless steel plates(100$\times$50 $mm^2$ and 50$\times$50 $mm^2$). The High Resolution Powder Diffractormeter of the Korea Atomic Research Institute was utilized in the measurement. The power of nuclear reactor was 24 MWt and the measured reflection in the 220 plane (2$\theta$）was $92.66^{\circ}$. Poisson ratio of 0.265 and elastic constant of 211 GPa were applied to the calculation of stresses and strains. Three directional components such as normal, transverse, and longitudinal stresses were measured. The results showed that three components were tensile and became compressive along the y axis in the zone away from the welded center. The compressive stresses became tensile in the zone away from the center line of x axis. This may be due to the balance effect caused by the net stress to keep the specimen shape flat.