• Journal of the Korean Society for Precision Engineering
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• v.17 no.1
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.437-442
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• 2014

The equipment or with a constant torque and a variable stress due to axial vibration such as the turbine-generator system in nuclear power plant show the fatigue fracture behavior. Thus this study whoul aim to measure the torsional stress and analyze the fatigue fracture behavior. To achieve this, we manufactured the equipment similar with turbine-generator system and applied various torsional vibration stress due to external load. In particular, the evaluation was conducted with the existing evaluation methods of the fatigue behavior of known stress-life, strain-life, crack growth assessment methods. With increasing the external load and independent methods tends to decrease the fatigue life was confirmed up to 10 times in 5 kV external load compared to without external load.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1132-1138
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• 2005

Fatigue life of metal material can be predicted by the use of fracture theory and experimental database. Although prediction of fatigue life of rubber material uses the same way as metal, there are many reasons to make it almost impossible. One of the reasons is that there is not currently used fracture criteria for rubber material beacuse of non-standardization, various way of composition process of rubber and so on. Tearing energy is one of the fracture criteria which can be applied to a rubber. Even if tearing energy relaxes the restriction of rubber composition, it is also not currently used because of complication to apply in. Research material about failure process of rubber and tearing energy was reviewed to define the process of fatigue failure and the applicability of tearing energy in estimation of fatigue life for rubber. Also, 1file element formulation of tearing energy which can be used in FE analysis was developed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.690-693
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• 2005

In this paper, probabilistic distribution of fatigue life of chassis component is determined statistically by applying the design of experiments and the Pearson system. To construct $p-\varepsilon-N$ curve, the case that fatigue data are random variables is attempted. Probabilistic density function(p.d.f) for fatigue life is obtained by design of experiment and using this p.d.f fatigue reliability about any aimed fatigue life can be calculated. Lower control arm and rear torsion bar of chassis component are selected as examples for analysis. Component load histories, which are obtained by multi-body dynamic simulation for Belsian load history, are used. Finite element analysis are performed using commercial software MSC Nastran and fatigue analysis are performed using FE Fatigue. When strain-life curve itself is random variable, probability density function of fatigue life has very little difference from log-normal distribution. And the case of fatigue data are random variables, probability density functions are approximated to Beta distribution. Each p.d.f is verified by Monte-Carlo simulation.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.2 s.191
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• pp.110-117
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• 2007

In this paper, probabilistic distribution of chassis component fatigue life is determined statistically by applying the design of experiments and the Pearson system. To construct p - ${\varepsilon}$ - N curve, the case that fatigue data are random variables is attempted. Probabilistic density function (p.d.f) for fatigue life is obtained by the design of experiment and using this p.d.f fatigue reliability, any aimed fatigue life can be calculated. Lower control arm and rear torsion bar of chassis components are selected as examples for analysis. Component load histories which are obtained by multi-body dynamic simulation for Belsian load history are used. Finite element analysis is performed by using commercial software MSC Nastran and fatigue analysis is performed by using FE Fatigue. When strain-life curve itself is random variable, the probability density function of fatigue life has very little difference from log-normal distribution. And the cases of fatigue data are random variables, probability density functions are approximated to Beta distribution. Each p.d.f is verified by Monte-Carlo simulation.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.372-377
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• 2008

Camber with positive deflection is one of the very important design parameters in the manufacture of railway coach. Positive camber is defined as concave shape such as an arch and it increases the strength of structure remarkably. But during the operation of a structure, the positive camber turns into negative camber and it loses the strength of structure. Therefore we should consider the camber effect when we evaluate the fatigue strength of negative cambered structure. For this purpose, we made a model of negative cambered locomotive car body and performed structural analysis and also we measured the dynamic loads at critical points during commercial line operation. Fatigue strength of locomotive was calculated by applying Miner's damage accumulation rule. Fatigue strength of the two locomotives which have different camber were compared to find out the effect of camber on dynamic load amplitude. We found that the more negative camber a locomotive had, the shorter fatigue strength obtained.

• 한국기계연구소 소보
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• s.13
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• pp.3-13
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• 1984

Fatigue failure of axle housing could cause many injuries and much financial loss. This challenges the engineer to improve design decisions involving fatigue. Endurance evaluation of axle housing is great interest to auto-mobile manufacturers for the sake of safety and reliability. Axle housing is subjected to gross vehicle weight(G.V.W)as mean load and alternating load. Theoretical design diagram involving mean and alternating stresses is used for the evaluation of axle housing fatigue endurance with the equivalent stress of fatigue critical area on the axle housing. Four point bending fatigue tests on axle housing with constant amplitude loading at approximately R=0 were performed with 50 ton servohydraulic strucural fatigue testing machine developed at KIMM. Specimens were made with the same material STKM 13B as the axle housing and tested to obtain S_N data. Five specimens of STKM 13B were tested at 253.61 MPa and weibull distribution was obtained at the same stress level. Material data and structural data were compares and fatigue stress property factor and fatigue life property factor were obtained.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.339-346
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• 2019

Various studies have been conducted to evaluate the probabilistic fatigue life of steel railway bridges, but many of them are based on a relatively simple model of crack propagation. The model assumes zero minimum stress and constant loading amplitude, which is not appropriate for the fatigue life evaluation of railway bridges. Thus, this study proposes a new probabilistic method employing an advanced crack propagation model that considers the live-dead load ratio for the fatigue life evaluation of steel railway bridges. In addition, by using the rainflow cycle counting algorithm, it can handle variable-amplitude loading, which is the most common loading pattern for railway bridges. To demonstrate the proposed method, it was applied to a numerical example of a steel railway bridge, and the fatigue lives of the major components and structural system were estimated. Furthermore, the effects of various ratios of live-dead loads on bridge fatigue life were examined through a parametric study. As a result, with the increasing live-dead stress ratio from 0 to 5/6, the fatigue lives can be reduced by approximately 30 years at both the component and system levels.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.83-85
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• 2006

The purpose of this study is to evaluate the fatigue life at the rib weldment of generator shaft. In order to do it, the stress distributions at the weldment under design loading condition were evaluated using FEA and analytical approach. The fatigue strengths of the as welded and toe machined rib specimen were estimated using 3-points bending fatigue test. Based on the fatigue test results, the S-N curve far the rib weldment of the generator shaft with post treatment was established.

• Korean Journal of Materials Research
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• v.17 no.8
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• pp.425-432
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• 2007

The microstructural evolution of ferritic 9Cr-1Mo-V-Nb steel, subjected to creep-fatigue at $550^{\circ}C$, was evaluated nondestructively by measuring the ultrasonic velocity. The variation of the ultrasonic velocity with the fatigue life fraction exhibited three regions. In the first region ($N/N_f$<0.2), a significant increase in the velocity was observed, followed by a slight increase between the fatigue life fractions of $0.2N_f$ and $0.8N_f$, and then a decrease in the final region. The change of the ultrasonic velocity during creep-fatigue was interpreted in relation to the microstructural properties. This study proposes an ultrasonic nondestructive evaluation method of quantifying the level of damage and microstructural change during the creep-fatigue of ferritic 9Cr-1Mo-V-Nb steel.