• Proceedings of the KSME Conference
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• 2003.04a
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• pp.261-266
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• 2003

The growth behavior of the transverse crack, which was one of the most dangerous damages of rail defects, was investigated under mode I and mixed mode loading in rail steel. In the case of variable amplitude loading, the fatigue crack growth behavior was discussed using characteristic stress intensity factor ranges ${\Delta}_{rms}$. In addition, characteristic comparative stress intensity factor ranges ${\Delta}_{V,rms}$ was proposed to evaluate the quantitative effects of the variable amplitude under mixed mode loading. As a result, crack growth rate under variable amplitude loading was faster than that under constant amplitude loading.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.2074-2082
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• 2000

In this study, to investigate and to predict the crack growth behavior under variable amplitude loading, crack growth tests are conducted on 7075-T6 aluminum alloy. The loading wave forms are generated by normal random number generator. All wave forms have same average and RMS(root mean square) value, but different standard deviation, which is to vary the maximum load in each wave. The modified Forman's equation is used as crack growth equation. Using the retardation coefficient D defined in previous study, the load interaction effect is considered. The variability in crack growth process is described by the random variable Z which was obtained from crack growth tests under constant amplitude loading in previous work. From these, a statistical model is developed. The curves predicted by the proposed model well describe the crack growth behavior under variable amplitude loading and agree with experimental data. In addition, this model well predicts the variability in crack growth process under variable amplitude loading.

• Structural Engineering and Mechanics
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• v.68 no.2
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• pp.193-201
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• 2018

This paper describes an experimental study on the seismic performance of steel reinforced concrete (SRC) T-shaped columns. The lateral loads were applied along the web of the column with different loading histories, such as monotonic loading, mixed loading of variable amplitude cyclic loading and monotonic loading, constant amplitude cyclic loading and variable amplitude cyclic loading. The failure modes, load-displacement curves, characteristic loads and displacements, ductility, strength and stiffness degradations and energy dissipation capacity of the column were analyzed. The effects of loading history on the seismic performance were focused on. The test results show that the specimens behaved differently in the aspects of the failure mode subject to different loading history, although all the failure modes can be summarized as flexural failure. The hysteretic loops of specimens are plump, and minimum values of the failure drift angles and ductility coefficients are 1/24 and 4.64, respectively, which reflect good seismic performance of SRC T-shaped column. With the increasing numbers of loading cycles, the column reveals lower bearing capacity and ductility. The strength and stiffness of the column with variable amplitude cyclic loading degrades more rapidly than that with constant amplitude cyclic loading, and the total cumulative dissipated energy of the former is less.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.654-661
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• 2001

In this study, fatigue growth behavior of the transverse crack, which was the most dangerous damage among the various types of rail defects, was investigated using the notched keyhole specimen under constant amplitude loadings. Fatigue limit of smooth specimen in rail steel at R=0 was 110MPa, and the fatigue crack initiation life in the region of the low stress amplitude (ie. long life) occupied the major portion of the total fatigue life. The fatigue strength under variable amplitude loading was converted to the equivalent fatigue strength based upon. Miners rule, which was estimated approximately 9% lower than that under constant amplitude loading. Also, in the low ΔK(sub)rms region ($\leq$21MPa√m), fatigue crack growth rate (da/dN) under constant amplitude loading was higher than that under variable amplitude loading, whereas the tendency was reversed in the high ΔK(sub)rms region. It is believed that this behavior is due to the transition of fracture appearance.

• Steel and Composite Structures
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• v.33 no.3
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• pp.433-444
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• 2019

Fatigue failure of a grid structure using bolt-sphere joints is liable to occur in a high-strength bolt due to the alternating and reciprocal actions of a suspension crane. In this study, variable amplitude fatigue tests were carried out on 20 40 Cr steel alloy M30 high-strength bolts using an MTS fatigue testing machine, and four cyclic stress amplitude loading patterns, Low-High, High-Low, Low-High-Low, and High-Low-High, were tested. The scanning electron microscope images of bolt fatigue failure due to variable amplitude stress were obtained, and the fractographic analysis of fatigue fractures was performed to investigate the fatigue failure mechanisms. Based on the available data from the constant amplitude fatigue tests, the variable amplitude fatigue life of an M30 high-strength bolt in a bolt-sphere joint was estimated using both Miner's rule and the Corten-Dolan model. Since both cumulative damage models gave similar predictions, Miner's rule is suggested for estimating the variable-amplitude fatigue life of M30 high-strength bolts in a grid structure with bolt-sphere joints; the S-N fatigue curve of the M30 high-strength bolts under variable amplitude loading was derived using equivalent stress amplitude as a design parameter.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.353-358
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• 2002

The purpose of this paper was to estimate the cumulative damage of pavement concrete by split tension fatigue test. The split tension fatigue test of variable amplitude loading were performed in two and three stages. The results of the fatigue test by variable amplitude loading showed that the sums of damage were greater than 1 in the increasing sequence loading tests, and less than 1 in the decreasing sequence loading tests. The remaining life estimated by equivalent damage theory was almost similar to that of experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1299-1306
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• 2011

In this study, crack-growth model parameters subjected to variable amplitude loading are estimated in the form of a probability distribution using the method of Bayesian parameter estimation. Huang's model is employed to describe the retardation and acceleration of the crack growth during the loadings. The Markov Chain Monte Carlo (MCMC) method is used to obtain samples of the parameters following the probability distribution. As the conventional MCMC method often fails to converge to the equilibrium distribution because of the increased complexity of the model under variable amplitude loading, an improved MCMC method is introduced to overcome this shortcoming, in which a marginal (PDF) is employed as a proposal density function. The model parameters are estimated on the basis of the data from several test specimens subjected to constant amplitude loading. The prediction is then made under variable amplitude loading for the same specimen, and validated by the ground-truth data using the estimated parameters.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.421-426
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• 2009

Recently, the design process for a railway bogie frame in Europe has been carried out according to the norm EN 13749. The activities in the norm EN shall demonstrate that the design of the bogie frame fulfills the acceptances of 4 steps of the program such as structural calculation, static tests, fatigue test and on-tracks tests. At the end of the acceptance program, the on-tracks tests have the aim to measure the real stress history generated in operation and to verify that they are reasonably next to those calculated and measured on the test rig. Therefore, in order to assure the safety of the railway vehicle, it is important to examined the durability of that under load histories measured from on-tracks tests. In this study, under variable amplitude loading based on the actual acceleration history, fatigue analysis of the welding bogie frame is investigated by using durability software. Moreover, the fatigue life of the frame under the loading in the norm EN fatigue test condition is evaluated and compared with the life under variable amplitude loading.

• International Journal of Railway
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• v.5 no.2
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• pp.71-76
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• 2012

Recently, axle load, operating speed and traffic density on railroads have had a tendency to increase and thereby cause additional pressure applied on used track. These operating conditions frequently result in service failure due to wear caused by wheel-rail contact and fatigue damage under cyclic loading. Among rail defects, the transverse crack, which has been the most dangerous type of fatigue damages, is developed from the subsurface crack near the rail running face and grows perpendicular to the rail surface. Therefore, it is necessary to investigate systematically the growth behavior of transverse crack for rail steel under mixed mode. In this study, the fatigue crack growth behavior of the transverse crack in rail steel was experimentally investigated under mixed-mode variable amplitude loadings.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.4
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• pp.79-88
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• 1986

A nonlinear cumulative damage theory, which can model the effects of the magnitude and sequence of variable amplitude fatigue loadings, is proposed. The concrete beam specimens are prepared and tested in four-point flexural loading conditions. The variable-amplitude fatigue loadings in two and three stages are considered. The present experimental study indicates that the fatigue failure of concrete is greatly influenced by the magnitude and sequence of applied, variable-amplitude fatigue loadings. It is seen that the linear damage theory proposed by Palmgren and Miner is not directly applicable to the concrete under such loading cases. The sum of the cumulative damage is found to be greater than 1 when the magnitude of fatigue loading is gradually increased and less than 1 when the magnitude of fatigue loading is gradually decreased. The proposed nonlinear damage theory, which includes the effects of the magnitude and sequence of applied fatigue loadings, allows more realistic fatigue analysis of concrete structures.