• Elastomers and Composites
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• v.20 no.3
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• pp.189-204
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• 1985

The purpose of this study is to examine the dynamic properties, especially the damping and fatigue properites, of NR vulcanizates and to find out the vulcanizate which can be used as damping materials in industry. The results of this study can be summarized as follows: 1. In the ODR test, the S-2 vulcanizate was the fastest one in terms of having reached to optimum cure times($t_{90}$) and, with the same formula, when 50phr of HAF carbon black loaded, the shortest optimum cure times has shown. 2. The S - 2 vulcanizate was the best than the others in the physical properties. In aging properties, however, the E - 1 vulcanizate appeared to be better than the other vulcanizates. 3. The results of the RDS test for the NR vulcanization system under the condition of 0.1% strain amplitude and 1 Hz frequency showed no connection between Tg and the the nature of the crosslinking system, but 50phr loading of HAF carbon black increased Tg. The damping values of vulcanizates in the elastic region showed a strong relations the damping values and the crosslinking system. The S - 2 vulcanizate with higher crosslink density had lower damping values than other vulcanizates, and furthermore, the SH - 2 vulcanizates with 50phr loading of HAF carbon black increased the damping values. 4. The Goodrich Flexometer test showed that the heat buildup for the gum NR vulcanizates was less than for those which contained 50phr of HAF carbon black. In particular, the fatigue life of the vulcanizate with lower damping values appeared to be longer than that of the vulcanizates with higher damping values. In the fatigue test, the increasment of the loading or the temperature, applied to the vulcanizates, appeared to be shorten their fatigue life.

• International Journal of Highway Engineering
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• v.2 no.2
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• pp.149-161
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• 2000

The stiffness of the subbase materials is represented by the resilient modulus, $M_R$, which are very important properties in the mechanistic design of flexible pavement system. However, the cyclic $M_R$ testing method is too complex, expensive, and time consuming to be applicable on a production basis. In this study, the alternative $M_R$ testing technique for subbase materials was developed using a free-free resonant column (FF-RC) test considering deformational characteristics of subbase materials. To estimate the deformational characteristics of subbase materials, effects of strain amplitude and mean effective stress on modulus of subbase materials were investigated. The $M_R$ values determined by alternative testing procedures matched well with those determined by standard $M_R$ test, showing the capability of the proposed methods being used in determining $M_R$ values.

• Steel and Composite Structures
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• v.39 no.4
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• pp.435-451
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• 2021

Shear lag effect was a significant mechanical behavior of steel-concrete composite beams, and the effective flange width was needed to consider this effect. However, the effective flange width is mostly determined by static load test. The cyclic vehicle loading cases, which is more practical, was not well considered. This paper focuses on the study of shear lag effect of the concrete slab in the negative moment region under fatigue cyclic load. Two specimens of two-span steel-concrete composite beams were tested under fatigue load and static load respectively to compare the differences in the negative moment region. The reinforcement strain in the negative moment region was measured and the stress was also analyzed under different loads. Based on the OpenSees framework, finite element analysis model of steel-concrete composite beam is established, which is used to simulate transverse reinforcement stress distribution as well as the variation trends under fatigue cycles. With the established model, effects of fatigue stress amplitude, flange width to span ratio, concrete slab thickness and shear connector stiffness on the shear lag effect of concrete slab in negative moment area are analyzed, and the effective flange width ratio of concrete slab under different working conditions is calculated. The simulated results of effective flange width are compared with calculated results of the commonly used specifications, and it is found that the methods in the specifications can better estimate the shear lag effect in concrete slab under static load, but the effective flange width in the negative moment zone under fatigue load has a large deviation.

• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.28-38
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• 2010

High temperature high cycle and low cycle fatigue deformation behavior of automotive heat resistant aluminum alloys (A356 and A319 based) were investigated in this study. The microstructures of both alloys were composed of primary Al-Si dendrite and eutectic Si phase. However, the size and distribution for eutectic Si phase varied: a coarse and inhomogeneous distributed was observed in alloy B (A319 based). A brittle intermethallic phase of ${\alpha}-Fe\;Al_{12}(Fe,Mn)_3Si_2$ was detected only in B alloy. Alloy B exhibited high fatigue life only under a high stress amplitued condition in the high cycle fatigue results, whereas alloy A showed high fatigue life when stress was lowered. With regard to the low-cycle fatigue result ($250^{\circ}C$) showing higher fatigue life as ductility increased, alloy A demonstrated higher fatigue life under all of the strain amplitude conditions. Fractographic observations showed that large porosities and pores near the outside surface could be the main factor in the formation of fatigue cracks. In alloy B. micro-cracks were formed in both the brittle intermetallic and coarse Si phasese. These micro-cracks then coalesced together and provided a path for fatigue crack propagation. From the observation of the differences in microstructure and fractography of these two automotive alloys, the authors attempt to explain the high-temperature fatigue deformation behavior of heat resistant aluminum alloys.

• Resources Recycling
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• v.31 no.6
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• pp.36-43
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• 2022

The general screen used to separate the particle size of recycled aggregate has restrictions when dealing with moisturized materials because of the blockage phenomenon. Therefore, in this study, to improve the separation efficiency of the conventional screen, the excellence of additional vibrating device based on spring was decided by a simulation experiment based on the discrete element method (DEM). The motion characteristic was investigated by analyzing the displacement, amplitude, and strain angle based on the spring design. Further, the particle motion was simulated by applying spring motion. The material flow and separation efficiency of the screen applied spring were confirmed as 9.2 kg/s and 97 %, respectively. Consequently, the improvement in the screen applied with blockage prevention spring was confirmed by comparing with the conventional screen.

• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.450-459
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• 2009

The aim of this study was to measure the initial dynamic modulus changes of light cured composites using a custom made rheometer. The custom made rheometer consisted of 3 parts: (1) a measurement unit of parallel plates made of glass rods, (2) an oscillating shear strain generator with a DC motor and a crank mechanism, (3) a stress measurement device using an electromagnetic torque sensor. This instrument could measure a maximum torque of 2Ncm, and the switch of the light-curing unit was synchronized with the rheometer. Six commercial composite resins [Z-100 (Z1), Z-250 (Z2), Z-350 (Z3), DenFil (DF), Tetric Ceram (TC), and Clearfil AP-X (CF)] were investigated. A dynamic oscillating shear test was undertaken with the rheometer. A certain volume ($14.2\;mm^3$) of composite was loaded between the parallel plates, which were made of glass rods (3 mm in diameter). An oscillating shear strain with a frequency of 6 Hz and amplitude of 0.00579 rad was applied to the specimen and the resultant stress was measured. Data acquisition started simultaneously with light curing, and the changes in visco-elasticity of composites were recorded for 10 seconds. The measurements were repeated 5 times for each composite at $25{\pm}0.5^{\circ}C$. Complex shear modulus G*, storage shear modulus G', loss shear modulus G" were calculated from the measured strain-stress curves. Time to reach the complex modulus G* of 10 MPa was determined. The G* and time to reach the G* of 10 MPa of composites were analyzed with One-way ANOVA and Tukey's test ($\alpha$ = 0.05). The results were as follows. 1. The custom made rheometer in this study reliably measured the initial visco-elastic modulus changes of composites during 10 seconds of light curing. 2. In all composites, the development of complex shear modulus G* had a latent period for $1{\sim}2$ seconds immediately after the start of light curing, and then increased rapidly during 10 seconds. 3. In all composites, the storage shear modulus G" increased steeper than the loss shear modulus G" during 10 seconds of light curing. 4. The complex shear modulus of Z1 was the highest, followed by CF, Z2, Z3, TC and DF the lowest. 5. Z1 was the fastest and DF was the slowest in the time to reach the complex shear modulus of 10 MPa.

• The Korean Journal of Physiology
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• v.28 no.2
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• pp.181-190
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• 1994

Endothelium-derived relaxing factor (EDRF) activates guanylate cyclase which mediates the formation of cGMP from GTP in vascular smooth muscle. It is well known that endothelium-dependent relaxation is impaired in spontaneously hypertensive rats (SHR). However, it is still unknown whether the impaired endothelium-dependent relaxation in SHR results from the reduced release of EDRF or from the decrease of vascular response to EDRF. We investigated the effects of cGMP on the contractility and Ca movement in the aorta of SHR and Wistar-Kyoto rats (WKY). The amplitude of the endothelium-dependent relaxation to actylcholine (ACh) was significantly less in SHR than in WKY. L-arginine $(10^{-3}M)$ did not increase endothelium-dependent relaxation in both strains. Sodium nitroprusside (SNP), an activator of guanylate cyclase, relaxed the 40 mM $K^+-induced$ contraction in a dose-dependent manner $(10^{-10}{\sim}10^{-6}\;M)$ in the endothelium-rubbed aortic strips of both strains. However, there was no significant difference in these relaxations between WKY and SHR. 8-bromo-cyclic guanosine monophosphate (8-Br-cGMP), a cell membrane-permeable derivative of cGMP relaxed the 40 mM $K^+-induced$ contraction in a dose-dependent manner $(10^{-6}{\sim}10^{-4}\;M)$ in the endothelium-rubbed aortic strips of both strains. Also norepinephrine $(10^{-6}\;M)-induced$ contractions in normal and Ca-free Tyrode's solution were suppressed by the pretreatment with 8-Br-cGMP $(10^{-4}\;M)$ in either strain. However, the amplitudes of suppression induced by 8-Br-cGMP were greater in SHR than that in WKY. Basal $^{45}Ca$ uptake and 40mM $K^+-stimulated\;^{45}Ca$ uptake were not suppressed by pretreatment with 8-Br-cGMP $(10^{-4}\;M)$ in single aortic smooth muscle cells of both SHR and WKY. From the above results, it is suggested that cGMP decreases Ca sensitivity in vascular smooth muscle cells and that the impaired endothelium-dependent relaxation in the aortic strips of SHR is not the result of a reduced vascular response to EDRF.

• Earthquakes and Structures
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• v.14 no.4
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• pp.323-336
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• 2018

Machine foundations with impact loads are common powerful sources of industrial vibrations. These foundations are generally transferring vertical dynamic loads to the soil and generate ground vibrations which may harmfully affect the surrounding structures or buildings. Dynamic effects range from severe trouble of working conditions for some sensitive instruments or devices to visible structural damage. This work includes an experimental study on the behavior of dry dense sand under the action of a single impulsive load. The objective of this research is to predict the dry sand response under impact loads. Emphasis will be made on attenuation of waves induced by impact loads through the soil. The research also includes studying the effect of footing embedment, and footing area on the soil behavior and its dynamic response. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of different soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depths within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil in addition to soil pressure gauges. It was concluded that increasing the footing embedment depth results in increase in the amplitude of the force-time history by about 10-30% due to increase in the degree of confinement. This is accompanied by a decrease in the displacement response of the soil by about 40-50% due to increase in the overburden pressure when the embedment depth increased which leads to increasing the stiffness of sandy soil. There is also increase in the natural frequency of the soil-foundation system by about 20-45%. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency. Moreover, the soil density increases with depth because of compaction, which makes the soil behave as a solid medium. Increasing the footing embedment depth results in an increase in the damping ratio by about 50-150% due to the increase of soil density as D/B increases, hence the soil tends to behave as a solid medium which activates both viscous and strain damping.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.3
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• pp.259-267
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• 2004

A finite element method is used to simulate interaction of laser-based ultrasounds with surface breaking tracks in elastic media. The laser line source focused on the surface of semi-infinite medium is modeled as a shear dipole in 2-D plane strain finite elements. The shear dipole-finite clement model is found to give correct directivity patterns for generated longitudinal and shear waves. The interaction of surface waves with surface breaking cracks (2-D machined slot) is considered in two ways. Both the source and receiver are fixed with respect to the cracks in the first case, while the source is moving in another case. It is shown that the crack depth tested in the range of 0.3-5.0mm $({\lambda}_R/d=0.21{\sim}3.45)$ can be measured using the corner reflected waves produced by the fixed laser source. The moving laser source is found to cause a large amplitude change of reflected waves near crack, and the crack whose depth is one order lower than the wavelength ran be detected from this change.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.436-444
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• 2013

This article presents the dynamic response of nano-scale plates using the nonlocal continuum theory and higher-order shear deformation theory. The nonlocal elasticity of Eringen has ability to capture the small scale effects and the higher-order shear deformation theory has ability to capture the quadratic variation of shear strain and consequently shear stress through the plate thickness. The solutions of transient dynamic analysis of nano-scale plate are presented using these theories to illustrate the effect of nonlocal theory on dynamic response of the nano-scale plates. The relations between nonlocal and local theories are discussed by numerical results. Also, the effects of nonlocal parameters, aspect ratio, side-to-thickness ratio, size of nano-scale plate and time step on dynamic response are investigated and discussed. The amplitude and cycle increase when nonlocal parameter increase. In order to validate the present solutions, the reference solutions are used and discussed. The theoretical development as well as numerical solutions presented herein should serve as reference for nonlocal theories as applied to the transient dynamic analysis of nano-scale structures.