• Proceedings of the KSME Conference
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• 2000.11a
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• pp.322-327
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• 2000

This paper investigates the time-dependent crack growth in X20CrMoV 12 1 steel weld joints. Crack growth test are carried out $545^{\circ}C$ on side-grooved 1/2T CT specimens under static loads. A simulated material is produced for the intercritical HAZ, where fracture normally occurs. Constitutive properties are obtained for the simulated HAZ material as well as for the base metal and weld metal. Finite element analyses of crack growth are performed on the models with and without a HAZ layer, using the experimental crack length-time history. The inclusion of HAZ layer increase the load line velocities significantly. The crack growth rates are correlated reasonably well with $C^*$. The smallest crack size for the validity of $C^*$ is found much smaller than the ASTM crack initiation size for 1T CT specimen of creep ductile materials.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.1
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• pp.382-389
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• 2012

The fabricated report attack will not only cause false alarms that waste real-world response efforts such as sending response teams to the event location, but also drains the finite amount of energy in a wireless sensor network. In this paper, we propose a probabilistic filtering method for sensor network security (PFSS) to deal with filtering for the fabricated report. On the basis of filtering scheme, PFSS combines cluster-based organization and probabilistic verification node assignment using distance of from cluster head to base station for energy efficiency and hot spot problem. Through both analysis and simulation, we demonstrate that PFSS could achieve efficient protection against fabricated report attack while maintaining a sufficiently high filtering power.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.625-634
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• 1986

The strain distribution on a welded aluminum alloy transition joint produced by a static tensile load has been measured using a moire method combined with photoelastic coating method. The test specimens were made of aluminum alloy 6061-T6 and 2014-T6 butt welded with ER-4043 filler metal, and were post welded heat treated (solid solution heat treatment 502.deg. C 70min.) and precipitated (artificial aging 171.deg. C 600min.) to cause an abrupt change of mechanical properties between the base metals and weld metal. The photoelastic epoxy rubber was cemented on the specimen grating which had been reproduced on the specimen surface by using an electropolishing. The measurements were compared with strains computed by Finite Element Analysis. The following results were abtained. (1) The maximum strain were distributed along the center line in the transverse directiion of the weld metal. (2) The strain gradient along the fusion line increased approaching the V-groove tip and the maximum value was observed at a quarter of width from the V-groove tip. (3) The moire method combined with photoelastic coating was proved very useful for real time strain measurement in the welded aluminum alloy transition joint.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.304-308
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• 2007

Failure phenomena in uni-axial tension test were experimentally and numerically investigated for AA6111-T4, AA5083-H18 and DP-Steel, which were friction-stir welded with the same and different thicknesses. Forming limit diagram(FLD) was measured using hemispherical dome stretching tests for base materials and also predicted by Hill's bifurcation and M-K theories for welded areas. Finite element simulations well predicted hardening behaviors, failure locations as well as failure patterns for the uni-axial tension tests especially utilizing very fine meshes and FLD along with stress softening.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.177-178
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• 2014

This work proposes a two-dimensional (2-D) laser scanning mirror actuator with a simple structure composed of one magnet and four coils. The mirror-actuating device generates 2-D scanning motions about two orthogonal axes by combining electromagnetic actuators of the conventional moving-magnet types. The magnet is attached to back side of the mirror placed inside of the moving frame. The four coils is placed on the base frame in a cross shape. We implement a finite element analysis to calculate magnetic flux in the electromagnetic system with the overall size of $20mm(W){\times}20mm(D){\times}13mm(H)$ for the mirror size of $8mm{\times}8mm$. The each moving-magnet type electromagnetic actuator has the motor constant 3.41 mNm/A and the restoring constant 1.75 mNm/rad and the resonance frequency of 58 Hz and the bandwidth of 80 Hz. The proposed compact and simple 2-D scanning mirror predicted advantages of large 2-D angular deflections, wide frequency bandwidth and low manufacturing cost.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.3
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• pp.167-175
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• 2002

In this paper, an analytical model is proposed for analyzing the hysteretic behavior of RC beam with relocated plastic hinge region under load reversals. The plastic hinge is modeled not to be concentrated on a point but to be distributed on a finite size in beam. This is based on the assumption that the plastic hinge is formed over a certain region, in which the curvature varies. Tangential matrix is reformed using stiffness coefficients including variales such as the length and location of plastic hinge region. In order to construct the hysteretic rule of hinge, modified Takeda rule is also proposed on the base of regression analysis for the previous test results. Previous specimens are analyzed using the proposed model and the result is compared with test result. On the result of the comparison, it was shown that the hysteretic behavior of beams with different location of plastic hinge region could be prediced using the proposed analytical process.

• Electrical & Electronic Materials
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• v.8 no.2
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• pp.176-183
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• 1995

The present work is concerned with the switching conduction characteristics of PI LB films in metal insulator metal sandwiches. By applying various DC voltage bias to MIM junctions, conduction characteristics of junctions can be changed between the high-voltage low-current(off) condition, the low-voltage high-current (on) condition and the medium(mid) condition. Switching conduction characteristics can be also observed in MIM junctions employing some aromatic compounds as insulators. Switching conduction characteristics is assumed to be owing to the existence of aromatic rings, space charge in films, impurities on metal-insulator interface, and difference in work functions of base and top electrodes metal. To study the conduction process of on, off, and mid conductions, we measured I-V, d$^{2}$V/d I$^{2}$-V characteristics of junctions with several different top electrodes under various temperatures. Small conductance changes of junctions can be measured by observing the second derivative, d$^{2}$V/dI$^{2}$, of I-V curve. A dynamical technique is used to get the second derivatives. That is, a finite modulation of the current is applied to the junctions and the second harmonic of the voltage is detected.

• Journal of Auto-vehicle Safety Association
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• v.7 no.1
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• pp.27-32
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• 2015

In order to protect occupant during car crash accident, Regulation and NCAP(New Car assessment Program) have been developed among various countries like U.S.A., Europe, Korea and Australia. Especially NCAP scores affect to sales of vehicles. So vehicle makers are trying to get good score in NCAP. Low leg injuries play an important role in Australia and Euro NCAP and these injuries are related with footrest design. Optimization of footrest design in early stage of vehicle development is necessary to obtain better and robust results of low legs during crash tests. In this paper, DFSS method and finite element model were used to optimize the low leg performance in small RHD vehicles. Compared with the lower leg injury of base model, the lower leg injury of proposed model was slightly improved and robustness was enhanced also.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1273-1290
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• 2015

JK wall is a shear wall made of lightweight EPS mortar and reinforced with a 3-D galvanized steel mesh, called JK panel, and truss-like stiffeners, called JK stiffeners. Earlier studies have shown that low strength lightweight concrete has the potential to be used in structural elements. In this study, seismic contribution of the JK infill walls surrounded by steel frames is numerically investigated. Adopting a hybrid numerical model, behavior envelop of the wall is derived from the general purpose finite element software, Abaqus. Obtained backbone would be implemented in the professional analytical software, SAP2000, in which through calibrated hysteretic parameters, cyclic behavior of the JK infill can be simulated. Through comparison with earlier experimental results, it turned out that the proposed hybrid modeling can simulate monotonic and cyclic behavior of JK walls with good accuracy. JK infills have a panel-type configuration which their dominant failure mode would be ductile in flexure. Finally technical and economical advantages of the proposed JK infills are assessed for two representative multistory buildings. It is revealed that JK infills can reduce maximum inter-story drifts as well as residual drifts at the expense of minor increase in the developed base shear.

• Nuclear Engineering and Technology
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• v.36 no.4
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• pp.316-326
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• 2004

The $40\%$ of wall criterion, which is generally used for the plugging of steam generator tubes, is applied only to a single crack. In a previous study, a total number of 9 failure models were proposed to estimate the local failure of the ligament between cracks, and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however known that parallel axial cracks are more frequently detected than collinear axial cracks during an in-service inspection. The objective of this study is to determine the plastic collapse model that can be applied to steam generator tubes containing two parallel axial through-wall cracks. Three previously proposed local failure models were selected as the candidates. Subsequently, the interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed to determine the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a COD base model was selected as an optimum model.