• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.440-447
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• 2005

In this study, strain measurement and its applicability to estimated deflection curve using fiber bragg grating sensors was conducted. For this purpose, reinforced concrete beams were made and sensors were attached both on the surface of the beams and inside steel. Two types of sensors were used to detect strain on the beams and steel : fiber bragg grating sensors, electric resistance strain sensors. So fatigue test is done with measuring strain of specimen. In addition, this experiments estimates the optimum deflection curve that converts strain curve data measured by FBG sensors into deflection.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.87-95
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• 1990

Rotating bending fatigue tests of an authentic steel 304 were performed at various temperatures such as room temperature, $538^{\circ}$ and $593^{\circ}C$. The plastic replica method was also applied in order to estimate the fatigue life on the basis of serial observation of small fatigue crack initiation and growth on the pit specimen surface. The fatigue crack growth behavior of 304 stainless steel was investigated within the frame work of elastic-plastic fracture mechanics within a narrow scatterband in spite of different stress levels at elevated temperature as at room temperature. The growth law of small surface crack is determined uniquely by the term. $\DELTA\sigma^{n}a$ where $\DELTA\sigma$ is the stress amplitude, a is the crack length, and n is a constant. It is found that the small crack growth behavior is basically equivalent to the S-$N_{f}$ relationship, where S and $N_{f}$ are stress and number of cycles to failure, and the fatigue life prediction is in good agreement with the experimental results.

• Tribology and Lubricants
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• v.31 no.1
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• pp.1-5
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• 2015

In this study, we apply an ultrasonic nanocrystal surface modification (UNSM) technique to radial journal bearings (JBs) and disks made of SUJ2 and SCM440, respectively. We investigate frictional properties of untreated and UNSM-treated specimens using a ball-on-disk tester. We construct the Stribeck curve at the boundary, under mixed and full hydrodynamic lubrication conditions for the specimens using friction data obtained from JB tests. The friction at the boundary lubrication condition and the transition period to mixed lubrication condition on the UNSM-treated specimens is reduced, which improves the service life of JBs. The major effects of this reduction in the three lubrication regimes can be explained in the terms of improved mechanical properties and the presence of micro dimples. Moreover, we estimate the friction and fatigue properties of SCM440 specimens using a ball-on-disk specimen under dry and oil-lubricated conditions. Friction test results reveal that the UNSM-treated specimens show lower friction coefficient than the untreated specimens under both dry and oil-lubricated conditions. We evaluate the fatigue properties of SCM440 specimens by calculating the Hertzian stress with respect to the failure cycles. Fatigue tests results also reveal that the UNSM-treated specimens possess a longer fatigue life than the untreated specimens. The improved properties are effective in increasing the energy efficiency of bearings.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.3
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• pp.1085-1090
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• 2011

To assure the safety of rolling stock, it is important to perform the fatigue analysis of reduction gear unit in rolling stock considering a variation of velocity and traction motor capability. This paper presents fatigue analysis of the damage of reduction gear unit of railway vehicle under variable amplitude loading(VAL) based on quasi-static fatigue analysis using finite element model and linear Miner's rule. The VAL for the simulation was constructed from the tractive effort curve and train run curves of railway vehicle under commercial operation condition using MSC.ADAMS dynamic analysis. The finite element model for evaluating the carburizing effect on the gear surface was used for predicting the fatigue life of the middle gear based on strain-life based approach. The results showed that the frequent high starting torque due to a quick start as well as increasing numbers of stops at station would decrease the fatigue life of reduction gear unit.

• Journal of Ocean Engineering and Technology
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• v.20 no.6 s.73
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• pp.88-92
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• 2006

Large-scale model tests of welded topside joints were carried out to observe the fatigue behavior of API 2W Gr.50 steel produced by POSCO. The fatigue crack behaviors for various loading conditions were measured and investigated around the critical joint sections. The experimental results have been verified with numerical approaches and also compared with the AWS D1.1 and DnV RP-C203 design curves. The large-scale experiment models were fabricated, based on the actual operating east area fixed platform. The dimensions of the models were slightly modified to accommodate the test facilities and capacities. The fatigue test was carried out having ${\Delta}Q$ of T1=705.6kN, T2=749.7kN and T3=793.8kN. The three specimens were statically loaded 20 times, with various loadings of about 50kN intervalsbetween the maximum and minimum loads required in the fatigue tests. This loading removed the residual stress in the specimen before the fatigue tests. The topside joint crack was initiated from the brace heel, where the maximum tensile stress occurred. The API 2W Gr.50 steel satisfied the AWS D1.1 detail category C and DnV RP-C203 detail category F ${\Delta}S-N$ curve.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2183-2190
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• 2000

A thermal aging is observed in a primary reactor cooling system(RCS) made of a casting stainless steel when the RCS is exposed for long period at the reactor operating temperature, 290~3300C An investigation of effects of thermal aging on a low cycle fatigue characteristics included a stress variations caused by a reactor operation and trip, is required. The purpose of the present investigation is to find an effect of a thermal aging of the CF8M on a low cycle fatigue life. The specimen of CF8M are prepared by an artificially accelerated aging technique holding 300 and 1800hr at 4300C respectively. The low cycle fatigue tests for the virgin and two aged specimens are performed at the room temperature for various strain amplitudes($\varepsilon$ta), 0.3, 0.5, 0.8, 1.0, 1.2 and 1.5% strain. Through the experiment, it is found that the fatigue life is rapidly reduced with an creasing of the aging time. The experimental fatigue life estimation formulas between the virgin and two aged specimen are obtained and are proposed to a analysis purpose.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1667-1674
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• 2010

The fatigue life is estimated while determining the reliability of aircraft structures. In this study, the estimation of fatigue life was carried out on the basis of a cumulative damage theory; the working S-N curve and the equivalent stress on the engine support structure significantly affect the safety of the aircraft. The maximum stress observed was 1,080 MPa in the case of scissors link under crash load condition, and there was a 5% margin for the allowable stress corresponding to the temperature reduction factor. The maximum stress was 876 MPa, and the stress equation coefficient had a maximum value of 0.019 MPa/N in the case of scissors link under fatigue loads. In the results of the fatigue life analysis, the safety life in a fretting area of scissors link upper part was 416,667 flight hour, and other parts showed to infinite life. Therefore, it was demonstrated that the fatigue life requirement of aircraft engine support structure (scissors link, straight link) could be satisfied.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.5
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• pp.15-21
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• 2009

The design of the stud shear connector of a bridge structure is mostly controlled by the fatigue resistance not by the strength, if it is followed by AASHTO LRFD Bridge Design Specification. This fatigue design code in AASHTO LRFD is based on the research work done by Slutter and Fisher in 1966. These tests seemingly underestimated the fatigue resistance of connectors because of the inherent eccentricity of the one-face test setup which results additional tension forces to the stud. In addition, the stress ranges were not plotted in the log scale, because it was not known at that time that the fatigue resistance of the welded steel structures has a linear relationship of log scales of stress range and number of loading cycles. This study evaluates the test data produced by the Slutter and Fischer, and plot the data on the proper manner. The fatigue push-out test data produced recently by many other researches all around the world are gathered and analyzed, furthermore a design curve is recommended.

• 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 : (${\sigma}_{f,20,R=-1}=285.1MPa$).

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.163-172
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• 2003

As concrete structures are getting larger, higher, longer, and specialized, it is more required to develop steel fiber concrete and apply to the real world. In this research, it is aimed to have fatigue strength examined, varying the steel fiber content by 0%, 0.75%, 1.00%, 1.25%, by experimental study of Two-spans Beam with Steel Fibrous with repeated loads. The ultimate load and the initial load of flexural cracking were measured by static test. In addition, the load versus strain relation, load versus strain relation, load versus deflection relation, crack pattern and fracture mode by increasing weight was observed. On the other hand, the crack propagation and the modes of fracture according to cycle number and the relation of cycle loading to deflection relation and strain relation was observed by fatigue test. As the result of fatigue test, Two-spans Beam without Steel Fibrous was failed at 60~70% of the static ultimate strength and it could be concluded that fatigue strength to two million cycle was around 67.2% by S-N curve. On the other hand, that with Steel Fibrous was failed at 65~85% of the static ultimate strength and it could be concluded fatigue strength to two million cycle around 71.7%.