• Transactions of the Korean Society of Mechanical Engineers A
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• 제39권6호
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• pp.597-602
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• 2015

CrMo alloy steel was nitrided using two types of processing methods, ion-nitriding processing and nitrocarburizing. Both processes were conducted for a duration of 30 min. To compare the surface hardness of the alloys created by the different processes, microhardness tests were conducted, and fatigue tests of each material were performed by a cantilever rotary bending fatigue test machine (Yamamoto, YRB 200) in the very high cycle regime ($N>10^7cycle$). Fractography of the fractured surfaces was conducted by scanning electron microscopy - to observe the fracture mechanisms of very high cycle fatigue and the effect of the nitriding process on the fatigue characteristics.

• Proceedings of the KSR Conference
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• 한국철도학회 2001년도 추계학술대회 논문집
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• pp.273-278
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• 2001

The transmission system of high speed train serve in the severe condition compared with those of other trains, namely, they have to transmit high power to run with high speed and they have to make maximum use of the limited space. To clarify the strength of gear for Korea High-speed train, a bending fatigue test is performed for the output gear of axle gear reduction unit. This paper reports the reviews of bending fatigue strength test method and the test results of output gear of axle gear reduction unit for high speed train.

• Journal of the Korean Society for Precision Engineering
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• 제17권1호
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• pp.61-67
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• 2000

Gears are the most commonly used parts in automotive and industrial applications. One of most common modes of gear failures is tooth breakage, which is usually produced by the bending fatigue failure. It is important to manufacture the gears which can withstand the applied stresses in view of safety and economic requirement. This paper deals with bending fatigue strength for cold forged bevel gear. Especially, to compare fatigue characteristics for manufacturing processes difference, bending fatigue tests of bevel gears made by three different processes respectively. Results indicate that the fatigue strength of bevel gear is improved by cold forging process. Intergranular fracture is found on fatigue fracture surface, and dimples are observed on final fracture surface. The fatigue failure cannot be considered as a deterministic quantity, but must be characterized statistically. This study proposes a method to estimate bending fatigue lift of the bevel gear using the probability-load-life and Weibull analysis.

• Journal of the Korean Society for Precision Engineering
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• 제14권9호
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• pp.61-67
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• 1997

Hardened layer and compressive residual stress created by carburized treatment effect on bending strength of gear massively. Also, shot peening treatment improves the strength of carburized gear as it does the hardness and residual stress of surface layer. In these days shot peening techniques are welcomed as one of physical improvement ways around the surface of materials. It is used widely because qualitative analysis of shot peening has become possible and surface treatment can be done with very little costs comparaed to other surface improvement methods. Therefore this study investigates the effect of shot peening in surface shape and bending fatigue strength after doing many kinds of shot peening treatments, then doing fatigue test and also explained characteristics of shot peening gear.

• Journal of the Computational Structural Engineering Institute of Korea
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• 제26권3호
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• pp.199-205
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• 2013

In this study, the methodology for the fatigue life prediction using finite element method(FEM) in wire, bundle and assembly level of the wire harness system and the development of the fatigue life test machine for the numerical analysis are investigated. To obtain stress-life(S-N) histories of the componential wires of the system, five kinds of wires are prepared and applied to the repeated bending motion using developed fatigue life test equipment. Equivalent model of the wire from the rule of mixtures theory is used for the material modeling of sheath and wire core combination. Contact conditions among the wires, taping conditions are established through the bundle level test and numerical bundle analysis. Wire and bundle level results are adopted for the assembly level analysis. For the assembly level analysis, real wire harness system including bundle and grommet is numerically modeled and applied contact condition between wires with real opening motion. The fatigue life more than 700,000 cycles of the assembly is obtained from the FEM, and it is confirmed that the result has good agreement with the experimental result.

• Journal of the Society of Naval Architects of Korea
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• 제37권2호
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• pp.118-126
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• 2000

TMCP steel has been widely used to construct ships and offshore structures. When it comes to ship and offshore structures, corrosion fatigue damages caused by sea water and fatigue occurred by wave-induced forces usually go on occurring simultaneously. So the fatigue life in corrosion environment is decreased markedly in comparison with that in air. The fatigue crack in corrosion easily initiates on welded joints of structure like as the fatigue crack in air. Therefore it is very important to study the fatigue properties of those of their welded joints as well as steel plates. In this study, rotary bending fatigue tests have been performed to investigate fatigue crack initiation and behavior of fatigue crack growth on CO2 gas weld HAZ of TMCP steel. The fatigue test used the specimens with various stress concentration factors in air and 3% NaCl solution

• Transactions of the Korean Society of Mechanical Engineers A
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• 제36권4호
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• pp.443-449
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• 2012

Nanoskins were fabricated on a Ti-6Al-4V material by carrying out various surface treatments, i.e., deep rolling, laser shot peening, and ultrasonic nanocrystal surface modification (UNSM). These surface treatments are newly developed techniques and are becoming more popular for industrial applications. Fatigue tests were carried out using material test system (MTS); these tests included the axial loading tension-compression fatigue test (R = -1, RT, 5 Hz, sinusoidal wave) and rotating bending fatigue test (R = -1, RT, 3200 rpm). The analysis of the crack initiation pattern in the UNSM-treated material indicated that the crack was interior originating in the axial loading tension-compression cycle, and was surface originating in the bending fatigue test. UNSM treatment significantly improved the fatigue strength for the regime of above $10^6$ cycles that S-N curve of rotating bending stress clearly show the performance of a 5 mm titanium specimen after UNSM treatment is similar to that of an untreated 6 mm titanium specimen.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제37권3호
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• pp.365-372
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• 2013

In this study, a statistical method for evaluating the fatigue life of a vehicle muffler was used to obtain reliable fatigue data using a limited number of specimens. Cyclic bending tests were conducted using specimens manufactured to be exactly the same as the mufflers installed in cars that are currently in use. To estimate the fatigue life by comparing the data obtained during the fatigue tests, the most suitable probability density function for the normal, lognormal, and Weibull distributions was selected. A goodness-of-fit test was performed on the probability distributions, and then a Weibull distribution using the least square method was selected. By using the selected Weibull distribution, the probability-moment-life curves (P-M-N curve) reflecting the fatigue characteristics were suggested as the data for the reliable design of a muffler.

• Journal of Advanced Marine Engineering and Technology
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• 제37권8호
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• pp.869-876
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• 2013

In order to estimate the fatigue life of mufflers at the early stage of researches and designs, the new prediction process was developed by the artificial neural network, which has the algorism of weldment properties. Bending fatigue test was carried out for defining the characteristics of muffler weldment fatigue life and damage. For considering and predicting mechanical and fatigue properties of the muffler, the maximum stress of weldment was adapted as the variable of artificial neural network training. Also, it was compared with the fatigue life predicting results using fatigue notch factors, for proving the newly developed process of the artificial neural network.

• Journal of the Society of Naval Architects of Korea
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• 제29권4호
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• pp.234-243
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• 1992

Fatigue crack initiation life has a wide scatter and this makes the fatigue design of structural members difficult. In order to make the fatigue life distribution clear, it is required to prepare a large number of specimens and repeat the fatigue tests under the same loading condition. Such fatigue tests usually take much time and cost. In this study, a fatigue testing method using a multi-notched test specimen for the purpose of estimating the distribution function of fatigue crack initiation life by small number of fatigue tests is used. The purpose of this study is to verify the above fatigue testing method of a multi-notched specimen by using Bayesian reliability analysis, Least square method and Skewness method for the determination of unknown Weibull parameters. The multi-notched specimen is a specimen in which several tens of statistically identical notches are prepared.