• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 추계학술대회 논문집(I)
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• pp.733-738
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• 2002

In this study, contact fatigue in wheel-rail contact is simulated. It is necessary to calculate contact stress and subsurface stresses accurately to predict fatigue behavior. Contact stresses are obtained by contact analysis of semi-infinite solid based on influence function and subsurface stress field obtained by using rectangular patch solutions. Based on these stress values, several multiaxial high-cycle fatigue criteria are used and the critical loads corresponding to fatigue limits are calculated. The simulation results show that the critical load is decreasing rapidly and the site of crack initiation also moves rapidly to the surface from the subsurface when friction coefficient exceeds a specific value for all of three fatigue criteria.

• Tribology and Lubricants
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• 제21권3호
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• pp.136-141
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• 2005

Analytical model to calculate the contact fatigue life of rough surface is presented in this paper. The effect of surface roughness can be calculated by this model. Computational method and the theoretical basis are also discussed. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. As a result of analysis the relationship between the life and the roughness as well as the most probable depth of the crack initiation is calculated.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1992년도 춘계학술대회 논문집
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• pp.268-273
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• 1992

Thin walled tubular specimens of 0.45% structural carbon steel were used in the bizxial tests. Biaxial fatigue tosts were conducted on strain control including fully reversed tension-compression and in phase tension torsion loadings. The predictions of the biaxial fatigue life were based upon the uniaxial low cycle fatigue test results. Fatigue lives were ranged from 10$\^$2/to 10$\^$5/cycles. Four multiaxial strain based theories have been developed to correlate biaxial fatigue experimdntal results. These theories showed good correlatins except for maximum shear strain theory. In uniaxial tests, crack behavior was observed that crack initiated in the maximum shear strain direction and propagated in the direction perpendicular to principal stross. But, in biaxial tests, both crack initiation and growth occured on the maximum shear strain direction only.

• KEPCO Journal on Electric Power and Energy
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• 제6권1호
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• pp.41-47
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• 2020

The contribution of damage mechanisms to failure of steam turbine casing made of Cr-Mo-V steel was investigated. Creep-fatigue interaction on the HP side corner of turbine casing was revealed as the root cause of the catastrophic failure performed by metallurgical analysis. The steady-state pressure and transient thermal stress were analyzed based on the actual operating condition of the thermal plant. Damage of creep-fatigue interaction to crack initiation was evaluated with multiaxial effects. The contribution ratio of creep and fatigue to the crack initiation was estimated to 3:1. Temporary geometrical correct action with repair weld was executed. For long-term operation, design improvement of casing equipment for creep resistance should be needed.

• Structural Engineering and Mechanics
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• 제62권6호
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• pp.739-748
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• 2017

Notches such as slots are typical geometric features on mechanical components that promote fatigue crack initiation. Unlike for components with open hole type notches, there are no conventional treatments to enhance fatigue behavior of components with slots. In this work we evaluate the viability of applying laser shock peening (LSP) to extend the fatigue life of 6061-T6 aluminum components with slots. The feasibility of using LSP is evaluated not only on damage free notched specimens, but also on samples with previous fatigue damage. For the LSP treatment a convergent lens was used to deliver 0.85 J and 6 ns laser pulses 1.5 mm in diameter by a Q-switch Nd: YAG laser, operating at 10 Hz with 1064 nm of wavelength. Residual stress distribution was assessed by the hole drilling method. A fatigue analysis of the notched specimens was conducted using the commercial code FE-Safe and different multiaxial fatigue criteria to predict fatigue lives of samples with and without LSP. The residual stress field produced by the LSP process was estimated by a finite element simulation of the process. A good comparison of the predicted and experimental fatigue lives was observed. The beneficial effect of LSP in extending fatigue life of notched components with and without previous damage is demonstrated.

• 한국자동차공학회논문집
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• 제12권4호
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• pp.94-100
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• 2004

A dynamic finite element analysis of a rig test model for truck chassis systems is conducted to establish an appropriate model designed to predict the fatigue life. A reference Belgian road input, which has been obtained from a field test, is imposed on the finite element model in the modal finite element analysis, and the resulting strain history is employed for the prediction of the fatigue life. This is compared with the prediction based upon the strain history measured in the field test. The two agree with each other within the limitation of the field data and the input data to the model. The high frequency responses over 50 Hz are confirmed to be negligible as far as their effect on the fatigue life is concerned.

• Steel and Composite Structures
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• 제38권3호
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• pp.271-280
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• 2021

In this study, the fatigue property of U rib-to-crossbeam connections in orthotropic steel bridge (OSB) crossbeams under heavy traffic vehicle load was investigated considering the effects of in-plane shear stress. The applicability of an improved structural stress (ISS) method was validated for the fatigue behavior analysis of nonwelded arc-shaped cutout regions in multiaxial stress states. Various types of fatigue testing specimens were compared for investigating the equivalent structural stress, fatigue crack initiation positions, and failure modes with the unified standards. Furthermore, the implications of OSB crossbeams and specified loading cases are discussed with respect to the improved method. The ISS method is proven to be applicable for analyzing the fatigue property of nonwelded arc-shaped cutout regions in OSB crossbeams. The used method is essential for gaining a reliable prediction of the most likely failure modes under a specific heavy traffic vehicle load. The evaluated results using the used method are proven to be accurate with a slighter standard deviation. We obtained the trend of equivalent structural stress in arc-shaped cutout regions and validated the crack initiation positions and propagation directions by comparing them with the fatigue testing results. The implications of crossbeam spans on fatigue property are less significant than the effects of crossbeams.

• Tribology and Lubricants
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• 제25권6호
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• pp.399-403
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• 2009

The objective of this paper is to predict pitting initiation by using a contact analysis and subsurface stress. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions. Subsurface stress field is obtained using rectangular patch solutions. It is used Mesoscopic multiaxial fatigue criterion to predict contact fatigue life. It is important to predict pitting initiation to enhance reliability of the mechanical elements. Pitting life prediction in the spur gears which are fundamental mechanical element is presented in this paper.

• Tribology and Lubricants
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• 제28권1호
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• pp.19-26
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• 2012

Rolling contact fatigue of an urban railway wheel was analysed during its rolling. A FEM analysis was performed using a 3D modelling of rail and wheel, considering the slope of the rail and nonlinear isotropic and kinematic hardening behavior of the rail and the wheel. The maximum von-Mises stress and contact pressure between the rail and wheel were 656.9 MPa and 1111.4 MPa, respectively, under axial load of 85 kN with friction coefficient of 0. The fatigue initiation life prediction relationships by strain-lifetime (${\varepsilon}$-N) and Smith-Watson-Topper method were drawn for the wheel steel as follows: $N_i=7.35{\times}10^6{\times}SWT^{-3.56}$ and $N_i=5.41{\times}10^{-9}{\times}(\frac{{\Delta}{\varepsilon}}{2})^{-5.77}$. The fatigue lifetimes of the wheel due to rolling contact were determined to be infinite by ${\varepsilon}$-N and SWT methods.

• 대한기계학회논문집A
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• 제33권10호
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• pp.1091-1098
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• 2009

In this paper, the procedure to estimate fatigue crack initiation life has been established by considering fretting wear and multiaxial stress states on the contact surface of press-fitted shafts. And a method to calculate the local friction coefficient during the running-in period of fretting wear process has been proposed. The predicted result of worn surface profile in the press-fitted shaft with non-linear local friction coefficient can avoid excessive wear depth estimation compared with that for the case of constant local friction coefficient. Furthermore, the predicted fatigue crack initiation lives based on Smith-Watson-Topper model considering the fretting wear are in good agreement with the experimental data. Consequently, the present method is valid not only for predicting worn surface profile, but also for assessing fatigue crack initiation lives considering the fretting wear during the running-in period in press fits.