• Journal of Power System Engineering
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• v.3 no.2
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• pp.51-56
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• 1999

Fatigue crack propagation rates and characteristics of the SA516-70 steel which is used for the low temperature pressure vessels, were studied in the room temperature of $10^{\circ}C$ and low temperature ranges of $-10^{\circ}C,\;-30^{\circ}C,\;-50^{\circ}C,\;and\;-70^{\circ}C$ with stress ratio of R=0.05. The obtained experimental results are as follows; 1) In the logarithmic relationship between the fatigue crack propagation rate(da/dN) and stress intensity factor K, the linear relationship was obtained up to da/dN > $8{\times}10^3$ mm/cycle in the same of room temperature, but in low temperature case, the relationship was extended to the range of low crack propagation rate. 2) The lower limit stress intensity factor of SA516-70 ${\Delta}K_{th}\;was\;23MPa\sqrt{m}$ and in the case of low temperature $-50^{\circ}C\;and\;-70^{\circ}C$, the crack propagation rate da/dN which showed a linear relation, reached rapidly to the ${\Delta}K_{th}$. As the results, the crack propagation rates of $-50^{\circ}C\;and\;-70^{\circ}C$ were lower than that of room temperature and according to the testing temperature the rates were decreased rapidly to the ${\Delta}K_{th}$. 3) On the relationship between the stress intensity factor ${\Delta}K$ and the track propagation cycle, the stress intensity factors of low cycle region was rapidly increased at low temperature, but ${\Delta}K$ was increased rapidly at room temperature of high cycle. 4) On the relationship between the fatigue crack propagation rate and cycle, the fatigue crack propagation rate showed higher gradient in the room temperature than the low temperature due to the increment in ductility at low temperature.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.240-245
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• 2000

Fatigue crack propagation rates and characteristics of the SA516-60 steel which is used for the low temperature pressure vessels, were studied in the room temperature of $25^{\circ}C$ and low temperature ranges of $10^{\circ}C,\; -10^{\circ}C,\; -30^{\circ}C,\; -50^{\circ}C, \;and\; -70^{\circ}C4 with stress ratio of R=0.05. The obtained experimental results are as follows; 1) In the logarithmic relationship between the fatigue crack propagation rate(da/dN) and stress intensity factor K, the linear relationship was obtained up to da/dN 〉$8\times10^{-3}$/mm/cycle in the same of room temperature, but in low temperature case, the relationship was extended to the range of crack propagation rate. 2) The lower limit stress intensity factor of SA516-60 $\DeltaK_{th}$ was 15.8MPa and in the case of low temperature $-50^{\circ}C\; and\; -70^{\circ}C$, the crack propagation rate da/dN which showed a linear relation, reached rapidly to the $\DeltaK_{th}$/. As the results, the crack propagation rates of $-50^{\circ}C\; and\; -70^{\circ}C$ were lower than that of room temperature and according to the testing temperature the rates were decreased rapidly to the $\DeltaK_{th}$/. 3) On the relationship between the stress intensity factor $\DeltaK$ and the crack propagation cycle, the stress intensity factors of low cycle region was rapidly increased at low temperature, but $\DeltaK$ was increased rapidly at room temperature of high cycle. 4) On the relationship between the fatigue crack propagation rate and cycle, the fatigue crack propagation rate showed higher gradient in the room temperature than the low temperature due to the increment in ductility at low temperature.

• Steel and Composite Structures
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• v.22 no.4
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• pp.875-888
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• 2016

The proper selection of materials for the intended use of the structural member is of particular interest. The paper deals with determining both the mechanical properties at different temperatures and the behavior in tensile creep as well as fatigue testing of tensile stressed specimens made of low alloy 42CrMo4 steel delivered as annealed and cold drawn. This steel is usually used in engineering practice in design of statically and dynamically stressed components. Displayed engineering stress - strain diagrams indicate the mechanical properties, creep curves indicate the material creep behavior while experimental investigations of fatigue may ensure the fatigue limit determination for considered stress ratio. Also, hardness testing provides an insight into material resistance to plastic deformation. Experimentally obtained results regarding material properties were: tensile strength (735 MPa / $20^{\circ}C$, 105 MPa / $680^{\circ}C$), yield strength (593 MPa / $20^{\circ}C$, 76 MPa / $680^{\circ}C$). Fatigue limit in the amount of 532.26 MPa, as maximum stress at stress ratio R = 0.25 at ambient temperature was calculated on the basis of experimentally obtained results. Regarding the creep resistance it is visible that this steel can be treated as creep resistant at high temperatures (including $580^{\circ}C$) when applied stress is of low level (till 0.2 of yield stress).

• Restorative Dentistry and Endodontics
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• v.17 no.2
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• pp.331-341
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• 1992

The purpose of this study was to measure the polymerization contraction stress of two types of composite resins; chemical cured type(Cliarfil F II, Kuraray, Japan) and photo-cured type(Photo-Clearfil Bright, Kuraray, Japan). The stresses of composite resin by contraction measured with specially designed measuring device(Fig. 1). The stresses caused by shrinkage during hardening of specimens were measured according to the type of composite resins, thickness of specimen(0.65, 1.30 and 1.95mm), and ratio of catalyst to base in case of only chemical cured composite resin(0.5, 1.0 and 1.5). As the composite resin specimen shrank on hardening, the load cell recorded force vs time automatically on pen-recorder(Toa, Japan) with a cross-head speed 60mm/hr at 0~10 voltages up to 2 hours. The experiments were conducted in a room maintained at $23{\pm}2^{\circ}C$ and relative humidity $50{\pm}10%$. The results were as follows. 1. The contraction stress during hardening was higher in photo cured composite resin than in chemical cured composite resin. 2. The contraction stress during hardening was increased with thickness of composite resin specimen. 3. In chemical cured composite resin, the polymerization contraction stress was decreased with ratio of catalyst and base. 4. The contraction stress during polymerization was higher in early time after insertion of photo cured composite resin and chemical cured composite resin.

• Structural Engineering and Mechanics
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• v.53 no.2
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.

• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.9-20
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• 2008

It is important to increase the economy and efficiency of the diaphragm of the steel box girder bridge design. In this study, an experimental test is performed in a 4-span steel box girder bridge, which was under constructed according to the dead load of slab concrete and vehicle load. The test result is analyzed to verify the stress distribution of the diaphragm and the middle span. Next, stresses on the vertical stiffener are analyzed according to height. Stresses on the diaphragm with equal height are arranged respectively. Also, the stress distribution of the diaphragm and the middle span. Next, stress on the vertical stiffeners are analyzed according to height. Stresses on the diaphragm with equal height are arranged respectively. Also, the vertical stiffeners in the diaphragm was studied, and using the analyzed results, the proper length of the ratio of vehicle load with curing concrete to vehicle load with asphalt is calculated in each part of the steel box girder bridge. The results provide data that serve as basis for an economical and efficient design for the steel box girder bridge diaphragm.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.12
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• pp.1027-1034
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• 2014

The shear stress on a surface due to the thin film fluid flow is an important issue. In case of a rotating disk, the fluid is delivered to the edge of the disk by centrifugal force, which acts as a body force on the fluid. Wear of a surface is affected by the shear stress acting on the surface and curvature. In this study, we utilize computational fluid dynamics software to model the ratio of curvature and local shear stress on solid surfaces. The key goal of the study is to determine an optimized curvature for the thin film fluid flow on a solid surface in order to minimize the local shear stress affecting the wear of this surface. Our results on the effects of curvature will be utilized for the design of devices that utilize thin film fluid flow on a solid surface, such as rotating-disk spray systems and thin film coating.

• Structural Engineering and Mechanics
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• v.72 no.2
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• pp.245-256
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• 2019

The experimentally determined mechanical behavior of the material under the prescribed service conditions is the basis of advanced engineering optimum design. To allow experimental data on the behavior of the material considered, uniaxial stress tests were made. The aforementioned tests have enabled the determination of mechanical properties of material at different temperatures, then, the material's resistance to creep at various temperatures and stress levels, and finally, insight into the uniaxial high cyclic fatigue of the material under different applied stresses for prescribed stress ratio. Based on fatigue tests, using modified staircase method, fatigue limit was determined. All these data contributes the reliability of the use of material in mechanical structures. Data representing mechanical properties are shown in the form of engineering stress-strain diagrams; creep behavior is displayed in the form of creep curves while fatigue of the material is presented in the form of S-N (maximum applied stress versus number of the cycles to failure) curve. Material under consideration was 18CrNi8 (1.5920) steel. Ultimate tensile strength and yield strength at room temperature and at temperature of $600^{\circ}C$: [${\sigma}_{m,20/600}=(613/156)MPa$; ${\sigma}_{0.2,20/600}=(458/141)MPa$], as well as endurance (fatigue) limit at room temperature and stress ratio of R = -1 : (${\sigma}_{f,20,R=-1}=285.1MPa$).

• Korean Journal of Breeding Science
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• v.43 no.5
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• pp.391-398
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• 2011

Physiological responses to salinity stress were evaluated in six rice genotypes differing in their tolerance to salinity at the seedling stage. Susceptible genotypes ('Dongjingbyeo', 'Hwayeongbyeo', and 'IR29') showed salt injury symptoms (mean 8.8) and higher visual score under salt stress than that of tolerant ones ('Pokkali', 'IR74009', and 'IR73571'). As salinity affects growth and physiological parameters, the six genotypes thus showed significant reduction because of salt stress. Tolerant Japonica/Indica bred lines ('IR74009', 'IR73571') showed lower reduction, 33.9%, 34.5%, and 50%, respectively, in plant seedling height, dry shoot weight and dry root weight than those of the susceptible Japonica varieties ('Dongjingbyeo', 'Hwayeongbyeo'), and the highest reduction under salt stress was observed in dry root weight, followed by dry shoot weight and seedling height, respectively. Shoot $Na^+$ concentration of IR74099 and IR73571 was lower than that of the susceptible varieties, 'Dongjinbyeo' and 'Hwayeongbyeo'. There were no significant differences among genotypes in root $Na^+$ concentration. Shoot $K^+$ concentration showed a reverse tendency compared to shoot $Na^+$ concentration. IR74009 and IR73571 had considerably lower ratio compared to 'Dongjinbyeo' and 'Hwayeongbyeo' in $Na^+/K^+$ ratio of their shoot and was not different the tolerant check, 'Pokkali'.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.151-163
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• 2006

This paper presents the interrelationship between undrained static and cyclic shear behavior. Laboratory works were performed through the undralned static and cyclic triaxial test using Nak-Dong River sand. And static triaxial test involved the triaxial extension test for comparison with cyclic shear behavior Cyclic triaxial test was performed with a variety of combination conditions of initial static shear stress $(q_{st})$ and cyclic stress $(q_{cy})$. In this result, the stress path of cyclic shear behavior was correspondent with static shear behavior passing the critical stress ratio (CSR) line because of the development of flow deformation. After that, a failure occurred according to failure line (FL) of static shear behavior. The stress path of cyclic shear behavior showed essentially the same with static shear behavior, although it appears a little different in test method.