• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.427-432
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• 1998

The objective of this research is to observe the actual response of low-rise nonseismic moment-resisting reinforced frame subjected to varied levels of earthquake ground motions. First of all, the reduction scale for the model was determined as 1 : 5 considering the capacity of the shaking table to be used. This model was, then, subjected to the shaking table motions simulating Taft N21E component earthquake ground motions, whose peak ground accelerations(PGA's) were modified to 0.12g, 0.2g, 0.3g, and 0.4g. The global behavior and failure mode were observed. The lateral accelerations and displacements at each story and local deformations at the critical portions of structure were measured. The base shear was measured by using specially made load cells. Before and after each earthquake simulation test, free vibration tests were performed to find the changes in the natural period and damping ratio of the model.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.567-572
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• 1998

Structural behavior of R/C deep beams was investigated and compared to those of specimens with CFRP Grids. Test results show that the crushing of compression strut for the unstrengthened R/C deep beams is changed to the group of several diagonal cracks at mid-depth within the sheat span. Strengthened specimens grow to be more ductile after the redistribution of internal force on the CFRP Grids. The failure mode and variations of strains in the specimens are dependent on the shear span-to-depth ratio. The lower the shear span-to-depth ratio, the bigger failure load and the less variations in strain are observed. Additional anchorage of CFRP Grids does not only cause the improvement in the internal resistance, but also control the brittle shear failure of specimen after reaching the maximum loads.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.585-591
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• 1998

In the case of reinforced concrete beams strengthening by steel plate, sometimes these beams collapse due to the stress concentration at the ends of steel plates before the design expected failure. This kind of failure is called premature failure. This study analyzes the behavior of strengthened RC beams to control premature failure of these plated beams with either changing the geometries at the ends of plates or strengthening steel plates beside the ends. The results from the former cases show that, the effect of expanded plates sections at the ends was very small, and the beams which are rounded the ends of plates effectively increased the initial rip-off loads about 14% compared with control beam but the ultimate loads was almost same. However, the beams in the latter cases effectively increased the initial and the ultimate rip-off loads with changing failure mode, especially around 14~19% in the ultimate rip-off load comparing with control beam.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.4
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• pp.494-502
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• 2003

The near-tip field of mode-I dynamic cracks steadily propagating in a strain softening material is investigated under plane strain conditions. The material is assumed to be incompressible and its deformation obeys the $J_2$ flow theory of plasticity. A power-law stress-strain relation with strain softening is adopted to account for the damage behavior of materials near the dynamic crack tip. By assuming that the stresses and strain have the same singularity at the crack tip. this paper obtains a fully continuous dynamic crack-tip field in the damage region. Results show that the stress and strain components the same logarithmic singularity of (In(R/r))$\delta$, and the angular variations of filed quantities are identical to those corresponding to the dynamic cracks in the elastic-perfectly plastic material.

• Proceedings of the KSME Conference
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• 2001.06c
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• pp.616-620
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• 2001

The wrinkling in the flange and wall of a part is a predominent failure mode in stamping of sheet metal parts. In many cases this wrinkling may be eliminated by appropriate control of the blank holding force(BHF), but BHF affects the draw depth. Although the wrinkles of flange have been made in the incipient stage of drawing, if the height of wrinkles is maintained under a prescribed limit by decrease or extinction of wrinkles in the course of drawing, small BHP can be allowed so that the depth of drawing could be increased. Authors research the variation of the wrinkles in flange in the course of square cup drawing by using aluminium A1015 and aluminium alloy A5052.

• Journal of Advanced Marine Engineering and Technology
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• v.15 no.4
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• pp.54-69
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• 1991

This study deals with the position control of a hydraulic cylinder system operated by two port 3-way high speed solenoid valve in Pulse-Width-Modulation mode, instead of using conventional electro-hydraulic servovalve. Due to the complexity and the relatively poor reliability of the servovalve, an actuator using simpler and more study high speed solenoid valve will be presented. The high speed solenoid valve acts as converters of electronic pulse signal to hydraulic ones. It has been pointed out that there are practical problems to be solved in the PWM system, that is (1) accuracy of positioning control becomes considerably insufficient because the system is affected by on/off action of the solenoid valves, and (2) serious nonlinerality appears in the valve characteristics as a result of the switching behavior of the valves. As a method to overcome these defects, the differential PWM driving method of a hydraulic cylinder that improved the steady-state-error, flow rate nonlinearity in simple PWM, and the hydraulic hunting of dead time compensated-PWM driving is proposed in this study.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.4 no.3
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• pp.39-47
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• 1995

This paper suggests generalize mathematica mode for the benefit of volumetric error analysis of a multi-axis machine tool machining a sculptured surfaces. The volumetric error, in this paper, is defined as a three dimensional error at the cutting point, which is caused by the geometric errors and the kinematic errors of each axis and alignment errors of the cutting tool. The actual cutting position is analyzed based on the form shaping model including a geometric error of the moving carriage, where a form shaping model is derived from the homogeneous transformation matrix. Then the volumetric error is obtained by calculating the position difference between the actual cutting position and the ideal one calculated from a Nonuniform Rational B-Spline named as NURES. The simulation study shows the effectiveness for predicting the behavior of machining error and for the method of error compensation.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.10
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• pp.67-76
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• 2008

In this research, a simple technique for designing PID controller, which guarantees robust stability for two-mass systems with parameter uncertainties as well as rigid-body behavior and zero steady-state error,is described. As well, such a PID controller is designed to mate two important frequencies, at which the given system is excited, very close so that an appropriate reference profile generated by using command shaping techniques can cover those two frequencies. Root-locus analysis. which shows traces of closed-loop poles for the given system, is used to design this PID controller. Finally, feedforward controller is added to improve tracking performance of the closed-loop system. Simulation for a system with a flexible mode and parameter uncertainties is executed to prove the feasibility of this technique.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.347-350
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• 2003

The metal forming behavior and defect formation in Ti-6Al-4V tube during hot backward extrusion were investigated. To predict the forming-defects such as shear band, inner cracks or surface cracks, dynamic material model(DMM) including Ziegler's instability criterion and modified Cockcroft-Latham fracture criterion(C-L model) were used. These models were coupled to the internal variables generated from FE analysis. The chilling effect and friction indicated a great influence on the deformation mode of the tube and the formation of surface cracks. The simulation results for the backward extrusion were compared with the experimental observations.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.10a
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• pp.321-326
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• 1995

The present study provides some experimental observations on the structural developments of bubbly flow and the void wave damping in vertical, circular channel with a large diameter, and discusses the channel size effect on them. It is observed that the developing mode of bubbly flow structures and its transition mechanism are influenced by the channel size as well as the bubble size, and that they are well revealed in the behavior of wave damping.