• Journal of the Korean Society for Nondestructive Testing
• /
• v.24 no.2
• /
• pp.142-150
• /
• 2004

A preliminary study of the behavior of ultrasonic guided wave mode in a pipe using a comb transducer for maintenance inspection of power plant facilities has been verified experimentally. The mode identification has been carried out in a pipe using the time-frequency analysis methods such as the wavelet transform(WT) and the short time Fourier transform (STFT), compared with theoretically calculated group velocity dispersion curves for longitudinal and flexural modes. The results are in good agreement with analytical predictions and show the effectiveness of using the time-frequency analysis method to identify the individual modes. It was found out that the longitudinal mode(0,1) is less affected by mode conversion compared with the other modes. Therefore, L(0,1) is selected as an optimal mode for the evaluation of the surface defect in a pipe.

• Structural Engineering and Mechanics
• /
• v.18 no.4
• /
• pp.493-516
• /
• 2004

This paper addresses the behavior and strength of structural walls with a concrete compressive strength exceeding 69 MPa. This information also enhances the current database for improvement of design recommendations. The objectives of this investigation are to study the effect of axial-load ratio on seismic behavior of high-strength concrete flexural walls. An analysis has been carried out in order to assess the contribution of deformation components, i.e., flexural, diagonal shear, and sliding shear on total displacement. The results from the analysis are then utilized to evaluate the prevailing inelastic deformation mode in each of wall. Moment-curvature characteristics, ductility and damage index are quantified and discussed in relation with axial stress levels. Experimental results show that axial-load ratio have a significant effect on the flexural strength, failure mode, deformation characteristics and ductility of high-strength concrete structural walls.

• Proceedings of the KSRS Conference
• /
• 2003.11a
• /
• pp.1046-1048
• /
• 2003

Recently, various researches in respect of the positioning technologies using satellites and the other sensors have made location-based services (LBS) more common and accurate. Consequently, concern about position information has been increasing. However, since these positioning systems only focus on user's position, it is difficult to know the user's attitude or detailed behaviors at the specific position. It is worthy to study on how to acquire such human attitude or behavior, because those information is useful to know the context of the user. In this paper, the sensor unit consisting of three dimensional accelerometer was attached to human body, and autonomously measured the perpendicular acceleration of ordinary human behaviors including activity modes such as walking, running, and transportation mode using transportation such as a train, a bus, and an elevator. Subsequently, using the classified measurement results, the method to identify the human activity modes was proposed.

• Steel and Composite Structures
• /
• v.34 no.5
• /
• pp.671-679
• /
• 2020

The new energy-based criterion, named Reinforcement Strain Energy Density (ReiSED), is proposed to investigate the fracture behavior of the cracked orthotropic materials in which the crack is embedded in the matrix along the fibers. ReiSED is an extension of the well-known minimum strain energy density criterion. The concept of the reinforced isotropic solid as an advantageous model is the basis of the proposed mixed-mode I/II criterion. This model introduces fibers as reinforcements of the isotropic matrix in orthotropic materials. The effects of fibers are qualified by defining reinforcement coefficients at tension and shear modes. These coefficients, called Reduced Stress (ReSt), provide the possibility of encompassing the fiber fraction in a fracture criterion for the first time. Comparing ReiSED fracture limit curve with experimental data proves the high efficiency of this criterion to predict the fracture behavior of orthotropic materials.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2003.06a
• /
• pp.1087-1090
• /
• 2003

In this study, experimental procedures were suggested to investigate the sloshing behavior of a liquid storage tank subjected to inevitably external vibrating conditions. For this purpose. liquid storage tank with rectangular cross section was made of an acrylic resin for the visualization of liquid fluctuation. A specially designed vibrator was used to provide a specified vibrating condition to the liquid storage tank. Extrapolation technique was applied to determine sloshing natural frequency by using various sloshing frequencies at each vibrating displacement and liquid contents at a fixed vibrating frequency. Sloshing mode was also determined from continuous images or liquid fluctuation captured from a video camera. In addition, change in the height of the liquid free surface was measured by using a floating target and a laser displacement sensor. It is found that the suggested method can be applicable to identify the sloshing behavior of liquid storage tank with rectangular cross section.

• Steel and Composite Structures
• /
• v.9 no.2
• /
• pp.173-189
• /
• 2009

This paper presents a study on the behavior and design of bolted stainless steel plates under in-plane tension. Using an experimentally validated finite element (FE) program strength of stainless steel bolted plates under tension is examined with an emphasis on plate bearing mode of failure. A numerical parametric study was carried out which includes examining the behavior of stainless steel plate models with various proportions, bolt locations and in two different material grades. The models were designed to fail particularly in bolt tear-out and material piling-up modes. In the numerical simulation of the models, non-linear stress-strain material behavior of stainless steel was considered by using expressions which represent the full range of strains up to the ultimate tensile strain. Using the results of the parametric study, the effect of variations in bolt positions, such as end and edge distance and bolt pitch distance on bearing resistance of stainless steel bolted plates under in-plane tension has been investigated. Finally, the results obtained are critically examined using design estimations of the currently available international design guidance.

• Korea-Australia Rheology Journal
• /
• v.17 no.4
• /
• pp.191-198
• /
• 2005

The static and dynamic rheological behavior of concentrated sodium dodecylsulfate (SDS) stabilized, deformability controllable polydimethylsiloxane (PDMS) emulsions is reported and comparisons made with silica (hard sphere) suspensions. Steady-mode measurements indicate 'hard' (viscoelastic) droplets behave as hard spheres, while 'soft' (viscous) droplets induce structural flexibility of the emulsion against shear. Dynamic-mode measurements reveal that viscoelasticity of droplets provides the great magnitude of elasticity for the 'hard' emulsion, while formation of planar films between droplets is the origin of the elasticity of 'soft' emulsions. Combination of steady and dynamic rheological behavior has enabled depiction of droplet structure evolution in relation to the shear stress applied, especially by taking advantage of the normal force that reflects the transient deformation of droplets.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.8
• /
• pp.2491-2500
• /
• 1996

An experimental and analytical investigation is performed to study the buckling behavior of composite laminates with an embedded delamination. It is of particular interest to veryfy whether delamination growth cddurs with continuming deformation after buckling of composite laminates with an embedded delamination. Experiments are conducted for [0/sub 4///90/sub 8//0/sub 4/]/sub r/ laminates with delamination size in which local buckling mode governs buckling. Results show that delamination growth occurs in hgigher load after buckling and is accompanid by other damage mechanisms such as splitting. Also, it is found that transverse deformation before difurcation buckling is due to initial imperfection and structure such as plate with small bending stiffness is sensitive to that.

• Proceedings of the KSR Conference
• /
• 1998.11a
• /
• pp.553-559
• /
• 1998

This thesis studied to evaluate the fatigue behavior and propagation of rail steel under welding line. Test of crack growth was performed by all member of rail under constant amplitude loading at the structures laboratory in Hongik University. The effect of the following parameters with initiated crack length on the bottom edge of rail were studied. Here, fracture mechanics mode is opening mode. and Testing Material is KS50N Rail. From analysis and experimented result on the three Point bending in the lab, This paper presented a effect of crack growth , shape and remaining service life. Further more, according to the variable crack length, variable section and the ratio of section the fatigue behavior and propagation were studied.

• Journal of Korean Society of Steel Construction
• /
• v.11 no.1 s.38
• /
• pp.33-42
• /
• 1999

In the present study, crack initiation criteria, static failure and tensile mode fatigue behavior for a rail steel are evaluated to assure the railway vehicle's safety. The transverse fissure, which is the most critical damage in the rail, is initiated by the maximum shear stress and its location is subsurface. In addition, the possibility of transition from the shear mode to the mixed mode increases with increasing the length of subsurface crack. Because of the brittleness by the welding, the fracture toughness of the welded part is lower than of the base metal. For low ${\Delta}K$, the stage II fatigue crack growth rates of the welded part is slower than of the base metal but, for high ${\Delta}K$, this different behavior for fatigue crack growth rate is nearly diminished. These trends are more remarkable for low stress ratio, R=0.1. It is believed that this behavior is caused by the change of the microstructure which that of the welded part is coarser than of base metal.