• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.401-406
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• 2002

The purpose of this research was to obtain fatigue property of pavement concrete by flexural fatigue test. The size of specimen used in fatigue tests was 10$\times$10$\times$46cm. The specimens of pavement concrete were fabricated using the concrete at job site. The fatigue tests were performed by applying into a constant amplitude loading. The flexural fatigue tests were performed by stress levels of 90%, 80%, 70% and 60%, and stress ratio of 0.1. From this research, the S-N relationship, S-N-P relationship were derived and Weibull probability density functions was plotted using the distribution parameters.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.2
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• pp.34-41
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• 1991

In this study, the equations of motion of the thin annular plate with uniform thickness were derived from the classical theory of the plate. In addition the distribution of the inplane stress and the natural frequency due to the change of the ratio of the outer radius to the inner radius was presented by the analytic method using the numerical analysis. Results were compared with those from the experiment. As a result, the strain of rotating circular plate increased as the radius and rpm became greater, and the strain of radial direction was two times greater than that of transverse direction. Besides, it was confirmed that the natural frequency increased according to the decrease of the radius keeping the thickness constant.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.291-295
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• 2002

O-ring seal is usual component part in various mechanical apparatus for sealing that makes efficient performance of the equipments. The sealing performance of O-ring is affected in environments of the O-rings, like that applied pressure, working temperature, pre-compressed ratio and materials. In this paper, a pressurized, compressed elastomeric bi-polymer O-ring inserted into a rectangular groove is analyzed numerically using the MARC finite element program. The calculated FEM results showed that bi-polymer O-ring that is manufactured by NBR for an inner and FFKM for an outer ring shows a low temperature distribution among various bi-polymer O-ring models. But, the normal contact stress between the flange and upper part of the O-ring is small compared to other bi-polymer model.

• Computers and Concrete
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• v.18 no.5
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• pp.969-982
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• 2016

This paper investigates the compressive fatigue behaviour of polypropylene fibre reinforced self compacting concrete with Granite Sawing Waste (GSW). An experimental programme was conducted to obtain the fatigue lives of fibre reinforced self compacting concrete (FRSCC) at various stress levels. The stress ratio was kept constant as 0.3. Compressive fatigue test was conducted on 60 cubic specimens with 100mm edge length and 0.1% of polypropylene fibres at a frequency of 0.05Hz. The test results indicate that the fatigue lives of concretes containing granite sawing waste follow the double-parameter Weibull distribution. The fatigue strength equations have been developed based on different probabilities of failure.

• Steel and Composite Structures
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• v.22 no.2
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• pp.277-299
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• 2016

In this paper, free vibration, forced vibration, resonance and stress wave propagation behavior in nanocomposite plates reinforced by wavy carbon nanotube (CNT) are studied by a mesh-free method based on first order shear deformation theory (FSDT). The plates are resting on Winkler-Pasternak elastic foundation and subjected to periodic or impact loading. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. In the mesh-free analysis, moving least squares (MLS) shape functions are used for approximation of displacement field in the weak form of motion equation and the transformation method is used for imposition of essential boundary conditions. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of elastic foundation coefficients, plate thickness and time depended loading are examined on the vibrational and stresses wave propagation responses of the nanocomposite plates reinforced by wavy CNT.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.1338-1342
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• 2006

This paper presents the theoretical approach to describe the wave propagation in the waveguide with varying cross-section. The waveguides considered in this paper are stepped-rod, tapered-rod, and stepped rod with a tapered section at the middle of wave-transmission. The wave transmission ratio for displacement, stress, and power was calculated for these three rods. The distribution of the stress and displacement along the stepped rod with a tapered section was calculated and compared with the results obtained by FEM analysis.

• Tunnel and Underground Space
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• v.6 no.1
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• pp.10-18
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• 1996

Arched openings are generally excavated in underground construction works. Since stress distribution around openings depends on geological structure in rock mass, any shape of arched openings fully conformed with in-situ stress condition should be recommended to maintain mechanical safety of structures. Shape of arched openings is specified by both roof curvature and height-width ratio, and especially this report presents deformation behaviors related with roof curvature. Scale model tests and numerical studies of various shaped openings are conducted, where rectangular opening shows the greatest convergence. Through the anlayses of various arched opengings, as radius of roof curvature is increased, roof lowering and sidewall closure are remarkably increased, whereas floor heaving is increased little by little. By the way, it is useful that displacements of openings are roughly estimated in the stage of preliminary investigation. To find out elastic displacements of arched openings with any roof curvature, regressional formula and charts by least square method are represented. In addition elastoplastic deformation behavoirs of arched openings concerning associated adn non-associated flow rule are discussed.

• Journal of Biosystems Engineering
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• v.35 no.3
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• pp.182-188
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• 2010

Post-Harvest processing engineering is a field that studies prevention of the quality change of agricultural products during sorting, packaging, storage, and distribution after harvested. In distribution steps, agricultural products could be damaged by physical force, it is the main reason of low quality and they lost value of commodities. This study was performed to find the vibration characteristics of the peach, and to find the extent of the damage on the peach by fatigue stress. The vibration data was obtained on expressway and the vibration characteristics of peach was used to find the damage on the peach. To analyze the vibration characteristics of peach, the resonance frequency and vibration transmissibility were measured. The resonance frequency of the peach was 167.98 Hz and the transmissibility was 4.06 at resonance point. It was 150 ~ 250 Hz that the transmissibility was more than 1. And the transmissibility in simulated test was measured. When the trasmissibility was more than 1, the range was 15 ~ 65 Hz, and when it was less than 1, the range was 65 ~ 175 Hz. When the transmissibility was about 1, the range was 5 ~ 15 Hz. The damage and the vibration cycle numbers of peaches were compared with input frequency and acceleration. More damage and less cycle number happened in 30 Hz than in 62.5 Hz. The reason was that the transmissibility of 30 Hz was higher and the vibration displacement in lower frequency was more. The more acceleration and cycle number increased, the more the bruising volume of peaches increased. The bruising volume ratio for vibration fatigue was measured according to input acceleration and cycle number. Using measured data, regression models for bruising volume ratio(BVR) was developed as a function of the acceleration(A) and cycle number(CN) as follows. BVR = a * $A^b*$ $(CN)^c$

• Steel and Composite Structures
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• v.18 no.2
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• pp.443-465
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• 2015

In this paper, an efficient and simple trigonometric shear deformation theory is presented for thermal buckling analysis of functionally graded plates. It is assumed that the plate is in contact with elastic foundation during deformation. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. Unlike the conventional trigonometric shear deformation theory, the proposed sinusoidal shear deformation theory contains only four unknowns. It is assumed that the mechanical and thermal non-homogeneous properties of functionally graded plate vary smoothly by distribution of power law across the plate thickness. Using the non-linear strain-displacement relations, the equilibrium and stability equations of plates made of functionally graded materials are derived. The boundary conditions for the plate are assumed to be simply supported on all edges. The elastic foundation is modelled by two-parameters Pasternak model, which is obtained by adding a shear layer to the Winkler model. The effects of thermal loading types and variations of power of functionally graded material, aspect ratio, and thickness ratio on the critical buckling temperature of functionally graded plates are investigated and discussed.

• Korea-Australia Rheology Journal
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• v.21 no.4
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• pp.269-280
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• 2009

The drop formation dynamics of a shear thinning, elastic, yield stress ($\tau_o$) fluid (Carbopol 980 (poly(acrylic acid)) dispersions) in silicone oil has been investigated in a flow-focusing microfluidic channel. The rheological character of each solution investigated varied from Netwonian-like through to highly non-Newtonian and was varied by changing the degree of neutralization along the poly (acrylic acid) backbone. We have observed that the drop size of these non-Newtonian fluids (regardless of the degree of neutralisation) showed bimodal behaviour. At first we observed increases in drop size with increasing viscosity ratio (viscosity ratio=viscosity of dispersed phase (DP)/viscosity of continuous phase (CP)) at low flowrates of the continuous phases, and thereafter, decreasing drop sizes as the flow rate of the CP increases past a critical value. Only at the onset of pinching and during the high extensional deformation during pinch-off of a drop are any differences in the non-Newtonian characteristics of these fluids, that is extents of shear thinning, elasticity and yield stress ($\tau_o$), apparent. Changes in these break-off dynamics resulted in the observed differences in the number and size distribution of secondary drops during pinch-off for both fluid classes, Newtonian-like and non-Newtonian fluids. In the case of the Newtonian-like drops, a secondary drop was generated by the onset of necking and breakup at both ends of the filament, akin to end-pinching behavior. This pinch-off behavior was observed to be unaffected by changes in viscosity ratio, over the range explored. Meanwhile, in the case of the non-Newtonian solutions, discrete differences in behaviour were observed, believed to be attributable to each of the non-Newtonian properties of shear thinning, elasticity and yield stress. The presence of a yield stress ($\tau_o$), when coupled with slow flow rates or low viscosities of the CP, reduced the drop size compared to the Newtonian-like Carbopol dispersions of much lower viscosity. The presence of shear thinning resulted in a rapid necking event post onset, a decrease in primary droplet size and, in some cases, an increase in the rate of drop production. The presence of elasticity during the extensional flow imposed by the necking event allowed for the extended maintenance of the filament, as observed previously for dilute solutions of linear polymers during drop break-up.