• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.83-90
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• 2008

The purpose of this study is to attempt to use broken red brick, which is categorized as impurities of circular aggregate to thick aggregate, as a replacement for concrete. Through the material test and performance test for each mixing rate of the broken red brick (0%, 30%, 60%), the following conclusion was reached by studying the material and structural characteristics of circular aggregate to the concrete. Even though broken red brick, which is categorized as impurities of circular aggregate, is mixed 30% with normal rubble, the compression strength, intensity strength, and curving strength was similar to that of concrete that uses normal rubble. Therefore, concrete beam made with broken red brick can be applied to the real construction field. Also, the study regarding the cutting test of the concrete that uses broken red brick and regarding applying and mixing admixture that can increase the ductility factor will be required in the future.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.04a
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• pp.21-24
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• 2005

Three dimensional circular braided Glass/Aramid hybrid fabric/epoxy resin composite was fabricated. FBG sensor was embedded along the braid yam in order to monitor the internal dimensional changes of the 3-D braid composite. The amount of cure and thermal shrinkage of epoxy resin was also determined using FBG sensor system. FBG sensors with different grating length were embedded and their response were compared. The thermo-optic coefficient of FBG sensor was measured by several preliminary experiments. The internal strain that measured by FBG sensor and electric strain gauge was compared during compressive test. The released residual strain of the fabricated tubular composite was estimated using cutting method. The internal strain of the composite was estimated using FBG sensor system, and the result was compared with the value from electric strain gauge. It was found that FBG sensor system is a very useful technique to investigate inside region of complicated structure.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.12 no.2
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• pp.1-8
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• 2003

Conventionally used linear or circular interpolator is undesirable for the precision machining of 3D free-form surface as the following reason: the transmission errors due to the huge number of data, discontinuity of segmentation, unsmooth motion speed. To this regard, modern CNC machine tools are designed with the function of machining arbitrary parametric curves. However, these systems don't consider the adaptive federate, which dominates the quality of the machining process. This paper proposes a NURBS interpolator for the constant material removal rate. That is accomplished by the variable federate using curvature of curve. The curvature-compensated feederate system has important Potential applications in ensuring part accuracy and protecting cutting tool. The simulated result show it can be applicable to the real machining.

• Tribology and Lubricants
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• v.12 no.4
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• pp.52-59
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• 1996

The results of the electrical contact conductivity of multi-contact spots accounting the surface roughness and the non-conductive films of different origins such as air, water, cutting oil, and machining oil are presented. The array of metal spheres compressed between two flat plates has been used for simulation of the contact behavior of multiple contact of solids, under normal loading. Measurement of electrical contact resistance has been made using the equipment providing the adequate accuracy in the range of micro Ohms. The data on electrical contact resistance have been compared with theoretical predictions using the multiple contact model of constriction resistance. The effect of single spot number and array on conductivity of contact has been evaluated. The results of the experiments show that the contact resistance are closely related to the number of loading cycles, form of surface roughness, and presence of non-conductive films that reduce the size of the real electrical contact spots.

• Journal of computational fluids engineering
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• v.5 no.2
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• pp.9-19
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• 2000

Transient aerodynamic response of an airfoil to a moving plane-flap is numerically investigated using the two-dimensional Euler equations with conservative Chimera grid method. A body moving relative to a stationary grid is treated by an overset grid bounded by a 'Dynamic Domain Dividing Line' which has an advantage for constructing a well-defined hole-cutting boundary. A conservative Chimera grid method with the dynamic domain-dividing line technique is applied and validated by solving the flowfield around a circular cylinder moving supersonic speed. The unsteady and transient characteristics of the flow solver are also examined by computations of an oscillating airfoil and a ramp pitching airfoil respectively. The transient aerodynamic behavior of an airfoil with a moving plane-flap is analyzed for various flow conditions such as deflecting rate of flap and free stream Mach number.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.633-638
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• 2000

This paper reports an example of flow-induced vibration in a very large plant and the whole procedure of reducing the vibration. During the operation of flue gas desurfurization unit of the thermal power plant, serious vibration occurred at all around the unit. The worst vibration was recorded on the heat exchanger surface, which weighed 180 tones, as 17.8 m/$s^2$ in vibration amplitude at 34Hz. To identify the vibration, frequency analysis on the response vibration, the expected excitation force and the system resonance was executed. This investigation revealed that the cause of the vibration was vortex shedding from the circular pipes in the heat exchanger. Vortices from the pipes excited acoustic resonance in the heat exchanger room, which, in turn, made the structure vibrate. Through inserting the baffles between the pipes, which had an effect of cutting the acoustic wave at resonance frequency, the vibration was eliminated dramatically.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1858-1863
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• 2003

The properties of a machine tool greatly affect machining quality since a machine tool has large variance in its features. Machine tool makers want to find best machining condition with the one that they have built. Machine builders need to develop test specimen since it helps finding characteristics of machine tools when the machining properties of the specimen are analyzed. This paper develops test specimen to identify features of the main spindle, the feeding device, and the frame of a machine tool. The specimen is machined with a high speed machine and the features of the machine are analyzed with test items. They are surface roughness, overshoot in axial movement, errors in circular movement, feeding with small movement, and compensational error. This work can improve usability for a machine tool in machining practice.

• Journal of KSNVE
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• v.9 no.6
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• pp.1200-1209
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• 1999

This paper reports a peculiar example of flow-induced vibration in a very large plant and the whole procedure of reducing the vibration. During the operation of flue gas desurfurization unit of the thermal power plant, serious vibration was dtected at all around the plant. The worst vibration was recorded on the heat exchanger surface, which weighed 180 tones, as 17.8 m/$s^2$ in vibration amplitude at 34 Hz. To identify the vibration, frequency analysis on the response vibration as well as on the expected excitation forces and the system resonance was executed. This investigation revealed that the cause of the vibration was vortex shedding from the circular pipes in the heat exchanger. Vortices from the pipes excited acoustic resonance in the heat exchanger room, which, in turn, made the structure vibrate. Through inserting the baffles between the pipes, which had an effect of cutting the acoustic wave at resonance frequency, the vibration was eliminated dramatically.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.374-377
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• 2009

Glass fiber reinforced nylon has been used in many plastic industries. Mechanical properties of reinforced plastics depend upon types of glass fiber as well as loading of glass fiber. Tensile properties of glass fiber reinforced nylon66 have been studied for different glass fiber types and sizes. Types of glass fibers were circular and flat, and diameters were 7, 10, and 13 micrometers. Orientations of glass fibers in the matrix of nylon66 have been analyzed through X-ray CT. Tensile specimens were prepared by cutting out of square plates of $100{\times}100{\times}3mm$ with different angles such as 0, 45, and $90^{\circ}$ to the flow direction. As the loading of glass fiber increases to 45 wt% tensile strength increases up 2.5 times compare with neat nylon66. Anisotropic tensile strength has been observed and minimum tensile strength was measured in the specimen cut from perpendicular to the flow direction.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.2
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• pp.58-64
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• 2008

The cutting process of materials is accompanied with the elastic and plastic deformation due to chucking forces in the boring process of thin holes on the turning. Upon removal of chucking forces at the end of process, the original shape is remained in the plastic deformation; on the other hand, it is modified in the elastic deformation due to spring back. Fixing materials by chucks on the turning has influence on roundness because the process is conducted with unbalanced distribution load induced from the fixing of three jaws. Moreover, the amount of spring back depends on the magnitude of fixing forces. We studied the change of roundness according to fixing forces as well as the method to reduce the influence of chucking forces.