• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.275-278
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• 2005

This paper presents a model for evaluating the contribution by arch action and frame action to shear resistance in shear-critical reinforced concrete beams without stirrup. The rotating angle softened truss model is employed to calculate the shear deformation of the web and the relative axial displacement of the compression and tension chord by the shear flow are also calculated. From this shear compatibility condition in a beam, the shear contribution by the arch action is numerically decoupled. The transverse strain obtained from the proposed model is selected for shear failure criterion. Using the failure criterion, shear strength of RC slender beams without stirrup is predicted.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.1
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• pp.40-46
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• 2011

This paper is to investigate the effects of the asymmetrical support stiffness on the stability of a supercritical driveshaft with asymmetrical shaft stiffness and anisotropic bearings. The equations of motion is derived for a system including a rigid disk, a massless flexible asymmetric shaft, anisotropic bearings and a support beam. The Floquet theory is applied to perform the stability analysis with the variation of the support stiffness, the shaft asymmetry, the shaft damping and the shaft speed. The results show that the asymmetric support stiffness is closely related to the stability caused by primary resonance as well as the supercritical operation. First, the stiffness variation can stabilize the system around primary resonance by weakening the parametric resonance from the shaft asymmetry. Second, it also improve the stability characteristics at a supercritical operation when the support stiffness is not so high relative to the shaft stiffness.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.539-544
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• 2001

The holographic measurement techniques can be applied to various industrial fields such as automobile, airplane, construction, electronics, medical, mechanics and physics. The visualization of fluids is very important in aerodynamics, heat transfer and stress analysis. There are classically optical methods such as shadowgraph, schlieren method, and Mach-Zehnder interferometry for visualizing the fluid flow phenomena. But, it is difficult to understand the continuous state of fluids well in those methods. In this study, the real-time holographic interferometer with high-speed camera is applied to the flow visualization. In addition, collimated laser beam and rotating wedge are used for recording and formation of carrier fringes, respectively.

• Structural Engineering and Mechanics
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• v.33 no.5
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• pp.543-560
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• 2009

The rotating Rayleigh-Timoshenko beam element based on B-spline wavelet on the interval (BSWI) is constructed to discrete short shaft and stiffness disc. The crack is represented by non-dimensional linear spring using linear fracture mechanics theory. The wavelet-based finite element model of rotor system is constructed to solve the first three natural frequencies functions of normalized crack location and depth. The normalized crack location, normalized crack depth and the first three natural frequencies are then employed as the training samples to achieve the neural networks for crack diagnosis. Measured natural frequencies are served as inputs of the trained neural networks and the normalized crack location and depth can be identified. The experimental results of fatigue crack in short shaft is also given.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.441-441
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• 2012

Noise and vibration performance plays an important role in the development of rotating components, such as engines, drivelines, transmission systems, compressors and pumps. The presence of torsional vibrations and other specific phenomena require the dynamic behaviour of systems and components to be designed accurately in order to avoid comfort and durability related problems. This paper provides an overview of the instrumentation and challenges related to torsional vibration testing. The accuracy and performance of five measurement techniques (high-speed incremental encoder, dual beam laser interferometer, zebra tape, zebra disc, direct pulse measurements with magnetic probe) is investigated by measurements on a Fiat Punto 1.4 liter engine. The potential sources of error are discussed to explain the inaccuracies of each technique.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.15 no.2
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• pp.93-98
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• 2006

This study provides a comprehensive experimental study on the dynamic characteristics of a flexible matrix composite(FMC) driveshaft. A primary objective is to verify the analytic results of the FMC drivetrain based on the equivalent complex modulus approach and the classical lamination theory. A test rig has been constructed, which consists of a FMC shaft, a foundation beam, bearings, external dampers and a driving motor. The frequency response functions and transient responses are obtained from the external excitation and the spin-up testings. It turns out that the analytic results are in good agreement with the experimental ones.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.288.2-288.2
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• 2014

InP quantum dots were grown by using the molecular beam epitaxy technique. Quantum dots are connected and composed string-like one-dimensional structure due to the strain field along [110] crystal direction. Two prominent photoluminescence transitions from normal quantum dots and string-like one-dimensional structure were observed which show strong optical anisotropy along [1-10] and [110] crystal directions. Both peaks also showed blue-shift while rotating emission polarization from [1-10] to [110] direction. Such optical transition behaviors are the consequence of the valence band mixing caused by strain field along the [110] crystal direction.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.902-909
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• 2006

In this study, three-dimensional rotordynamic analyses have been conducted using equivalent beam, hybrid and fun three-dimensional models. The Present computational method is based on the general finite element method with rotating gyroscopic effects of a rotor system. General purpose commercial finite element code, SAMCEF which includes practical rotordynamics module with various types of rotor analysis methods and bearing elements is applied. For the purpose of numerical verification, comparison study for a benchmark rotor model with support bearings is performed first. Detailed finite element models based on three different modeling concepts are constructed and then computational analyses are conducted for the realistic and complex three-dimensional rotor system. The results for rotor stability and mass unbalance response are presented and compared with the experimental vibration test conducted in this study.

• Applied Microscopy
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• v.46 no.1
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• pp.14-19
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• 2016

Currently, focused ion beams (FIB) are widely used for specimen preparation in atom probe tomography (APT), which is a three-dimensional and atomic-scale compositional analysis tool. Specimen preparation, in which a specific region of interest is identified and a sharp needle shape created, is the first step towards successful APT analysis. The FIB technique is a powerful tool for site-specific specimen preparation because it provides a lift-out technique and a controllable manipulation function. In this paper, we demonstrate a general procedure containing the crucial points of FIB-based specimen preparation. We introduce aluminum holders with moveable pin and an axial rotation manipulator for specimen handling, which are useful for flipping and rotating the specimen to present the backside and the perpendicular direction. We also describe specimen preparation methods for nanowires and nanopowders, using a pick-up method and an embedding method by epoxy resin, respectively.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.124-127
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• 2007

In this study, we focused on investigation of governing parameters affected on the fatigue properties in the hyper-eutectoid steel wires used for TBR tires. Steel wires are fabricated under different drawing strain from 3.36 to 3.80. Their diameters are 0.21 mm and 0.185mm, respectively. The fatigue properties was measured by hunter rotating beam tester, specially designed thin-sized steel wires. The results showed that the fatigue properites of steel wire, marked as A-1, were greater than the others, due to the low value of residual stress. In order to elucidate the variations of fatigue properties, the microstructure, surface defect and residual stress were observed and measured by useful analysis technique, such as TEM, 3D profiler and FIB.