• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.153-156
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• 2006

A turbine stage consists of a stator and rotor. A stator provides the required inlet flow conditions so that a rotor can produce the necessary power. Passing wakes generated at the trailing edge of a stator make an interaction with a rotor. In the present study, this interaction flow mechanism is investigated using the numerical analysis. In case of the large gap distance between the stator and rotor, the stator and rotor flow analysis can be separated. First, only the stator flow field is solved. Second, the rotor flow field is solved including the passing wake information from the stator analysis. The passing wake experiences the shearing as it approaches to the rotor leading edge. And it is chopped when it strikes the rotor body. After that, the chopped wakes becomes the prolongation as it goes downstream. Also, the aerodynamic characteristics with the variation of the gap distance between a stator and rotor was investigated. Pressure jumps due to the passing wakes result in the pressure and lift loss and it gets stronger with the closer gap distance. This unsteady effect proves to be directly related to the fatigue and noise in turbomachinery and this study would be helpful to investigate such fields.

• Journal of Mechanical Science and Technology
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• v.19 no.4
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• pp.968-975
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• 2005

The shearing process for the sheet metal is normally used in the precision elements such as semi-conductor components. In these precision elements, the burr formation brings a bad effect on the system assembly and demands the additional de-burring process, so this imposes high cost on manufacturing. In this paper, we have developed the in-situ auto-aligning precision meso-punching system to investigate the burr formation mechanism and ultimately minimize burr. Firstly, we introduced the punch-die contact sensing method to align the punch and the die at initial state prior to the punching process. Secondly, by using the low-price semi-con­ductor laser, burr formed on the edges is measured intermittently during the punching process. We could, finally, make burr on the sheet metal uniformized and minimized by controlling of the precision X - Y table, $1\;{\mu}m$ resolution, and measuring burr height by semiconductor laser. Experimental results show the validity of our system for pursuing the burr-free punched elements.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.9
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• pp.55-62
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• 2003

This paper investigates the micro-cutting of cemented carbides using PCD (polycrystalline diamond) and PCBN (polycrystalline cubic boron nitride) cutting tools are performed with SEM direct observation method. The purpose of this study is to make clear the cutting mechanism of cemented carbides and the fracture of WC particles at the plastic deformation zone in orthogonal micro-cutting. And also to achieve systematic understanding, the effect of machining parameter on chip formation and machined surface was studied, including cutting speed, depth of cut and various tool rake angle. Summary of the results are shown below. (1) Three type of chip formation process have been proposed by the results of the direct observation in orthogonal micro-cutting of cemented carbide materials. (2) From the whole observation of chip formation, primary WC particles are crushed and/or fine grained in the shearing deformation zone. A part of them are observed to collide directly with a cutting edge of tool by following the micro-cutting. (3) Surface finish, surface morphology and surface integrity is good to obtain by cutting with PCD cutting tool compared with PCBN. (4) The machined surface has the best quality near the low cutting speed of 10${\mu}m$/sec with a cutting depth of 10 ${\mu}m$ using 0$^\circ$ rake angle and 3$^\circ$ flank angle in this condition, but it was found that excessively low speed, for example the extent of 1 ${\mu}m$/sec, is not good enough to select for various reason.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1824-1827
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• 2003

The sheet metal shearing process is normally used in the precision elements such as semi-conductor components. In precision elements, burrs usually reduce the quality of machined parts and cause interference, jamming and misalignment during assembly procedures and because of their sharpness, they can be safety hazard to personnel. Furthermore, not only burrs are hard to predict and avoid, but also deburring, the process of removing burrs, is time-consuming and costly. In order to get the burr-free parts, therefore, we developed the precise burr measuring system using the laser. The laser burr measuring system consists of the laser probe, the photo detector, the achromatic doublet lens, and the rotary ＆ the X-Y table. In previous reports, we used simple vertical measuring method. But, as we used relatively bigger laser spot diameter and had the limited reflection angle, it was difficult to obtain the precise measuring results. So called, the spot size effect makes the profile of burr measured distorted and the burr height measured smaller. By introducing the novel laser measuring method which employing the achromatic lens system and the tilting mechanism, we could make the spot size smaller and get the appropriate beam direction angle. Through the experiments, the accuracy of the developed system is proved. The burr height measured during the punching process can be used for automatic deburring and in-situ aligning.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.912-917
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• 2003

In this paper a new truss modeling technique for describing the beam shear resistance mechanism is proposed based on the reinterpretation of the well-known relationship between shear and the rate of change of bending moment in a reinforced concrete beam subjected to combined shear and moment loads. The core of the model is that a new perspective on the shear resistance can be gained by viewing the internal stress filed in terms of the superposition of two base components of shear resistance; arch action and beam action. The arch action can be described as a simple tied-arch which is consisted of a curved compression chord and a tension tie of the longitudinal steel, while the beam action between the two chords can be modeled as a membrane shearing element with forming a smeared truss action. The compatibility of deformation associated to the two action is taken into account by employing an experimental factor or internal state force factor a. Then the base equation of V=dM/dx is numerically duplicated. The new model was examined by the 362 experimental results. The shear strength predicted by the internal force state factor a show better correlation with the tested values than the present shear design.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.3
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• pp.111-117
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• 1997

The sudden-stop apparatus is made to measure the residual stress of the infinitesimal area at the turning work surface by using the X-ray stress apparatus. This study is trued to make the cutting work the instantaneous stopping state in the normal working state. The behaviour of work material near the tool is estimated. The estimation method is that the distribution of residual stress can be also measured. The object is to clarify and control the mechanism to leave the adequate stress of the finishing surface. It's beginning is due to observe the occurrence state of the residual stress at the cutting work. The result obtained by this study is as follows. The chips are not separated from the work materials at all the cutting experiments of built-up edges or the shearing areas etc. which can be precisely observed by using the sudden-stop apparatus. The strain of movable system which can be seen at the part of working layer means the size of strain. This experiment proves that the working strain should be lessened to make the size of strain control the residual stress happened at the cutting surface.

• The Korean Journal of Physiology and Pharmacology
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• v.19 no.1
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• pp.35-42
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• 2015

In cardiovascular disorders, understanding of endothelial cell (EC) function is essential to elucidate the disease mechanism. Although the mouse model has many advantages for in vivo and in vitro research, efficient procedures for the isolation and propagation of primary mouse EC have been problematic. We describe a high yield process for isolation and in vitro culture of primary EC from mouse arteries (aorta, braches of superior mesenteric artery, and cerebral arteries from the circle of Willis). Mouse arteries were carefully dissected without damage under a light microscope, and small pieces of the vessels were transferred on/in a Matrigel matrix enriched with endothelial growth supplement. Primary cells that proliferated in Matrigel were propagated in advanced DMEM with fetal calf serum or platelet-derived serum, EC growth supplement, and heparin. To improve the purity of the cell culture, we applied shearing stress and anti-fibroblast antibody. EC were characterized by a monolayer cobble stone appearance, positive staining with acetylated low density lipoprotein labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate, RT-PCR using primers for von-Willebrand factor, and determination of the protein level endothelial nitric oxide synthase. Our simple, efficient method would facilitate in vitro functional investigations of EC from mouse vessels.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.57-64
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• 2007

Since matric suction of unsaturated soil was related to soil and ground water contaminations, it is very important to analyze its mechanism that was represented by shear characteristics. In three phases of soil, a little air makes the condition of unsaturated soil on contract or shrinkage surface between water and air. Capillarity and suction in pore of unsaturated soil cause surface tension and surface force so it makes negative pore water pressure and increases effective stress as a result. Therefore, negative pore water pressure in partially saturated soil affects the soil structure and degree of saturation and it is important to evaluate accurately unsaturate flow and behavior. In this study, the shear strength characteristics of the seven sandy soils were investigated using consolidated drained triaxial tests with special emphasis on the effects of the negative pore pressure and the matric suction. These tests involved shearing under either a constant net confining pressure and varying matric suction or under a constant matric suction and varying net normal stress.

• Geomechanics and Engineering
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• v.35 no.2
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• pp.209-219
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• 2023

This paper presents numerical investigations into the particle crushing effect on the shear properties of gravel under direct shear condition. A novel particle crushing model was developed based on the octahedral shear stress criterion and fragment replacement method. A series of direct shear tests were carried out on unbreakable particles and breakable particles with different strengths. The evolutions of the particle crushing, shear strength, volumetric strain behavior, and contact force fabric during shearing were analyzed. It was observed that the number of crushed particles increased with the increase of the shear displacement and axial pressure and decreased with the particle strength increasing. Moreover, the shear strength and volume dilatancy were obviously decreased with particle crushing. The shear displacement of particles starting to crush was close to that corresponding to the peak shear stress got. Besides, the shear-hardening behavior was obviously affected by the number of crushed particles. A microanalysis showed that due to particle crushing, the contact forces and anisotropy decreased. The mechanism of the particle crushing effect on the shear strength was further clarified in terms of the particle friction and interlock.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.5
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• pp.187-193
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• 2006

A new jointing method using steel cramps with a unique configuration was developed for the field joint of precast deck slabs of highway bridges. In this jointing method, the looped distribution bars are connected by the cramps to the main reinforcements. Therefore, the joint can transfer the bending moment and shearing force through the interlocking effect caused by the cramps, and it is both excellent in installation on-site and economical compared with the loop joint currently in use. In order to confirm the bending and shear capacities and to clarify the failure mechanism of the joint, a series of static loading tests were carried out. From the results of these experimental studies, it was clarified that the cramp joint has enough load carrying capacity being equivalent to the loop joint.