• Journal of Korean Society of Industrial and Systems Engineering
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• v.39 no.2
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• pp.1-10
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• 2016

In this paper, we present a new way to derive the mean cycle time of the G/G/m failure prone queue when the loading of the system approaches to zero. The loading is the relative ratio of the arrival rate to the service rate multiplied by the number of servers. The system with low loading means the busy fraction of the system is low. The queueing system with low loading can be found in the semiconductor manufacturing process. Cluster tools in semiconductor manufacturing need a setup whenever the types of two successive lots are different. To setup a cluster tool, all wafers of preceding lot should be removed. Then, the waiting time of the next lot is zero excluding the setup time. This kind of situation can be regarded as the system with low loading. By employing absorbing Markov chain model and renewal theory, we propose a new way to derive the exact mean cycle time. In addition, using the proposed method, we present the cycle times of other types of queueing systems. For a queueing model with phase type service time distribution, we can obtain a two dimensional Markov chain model, which leads us to calculate the exact cycle time. The results also can be applied to a queueing model with batch arrivals. Our results can be employed to test the accuracy of existing or newly developed approximation methods. Furthermore, we provide intuitive interpretations to the results regarding the expected waiting time. The intuitive interpretations can be used to understand logically the characteristics of systems with low loading.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.3-8
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• 2002

In this study, extremely low cycle fatigue tests were carried out under push-pull loading conditions using graphite cast iron (GCD). In order to clarify the fatigue fracture mechanism of GCD in an extremely low cycle fatigue regime successive observations of internal fatigue damage were performed. The results obtained are as follows. (1) The process of extremely low cycle fatigue can be classified into three stages which are composed of the generation, growth and coalescence of microvoids inside materials. (2) In an extremely low cycle fatigue regime, microvoids originate from debonding of graphite-matrix interface.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.671-678
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• 2019

In this paper, the low cycle fatigue failure and ratcheting behavior, as well as their interaction of AH32 steel were experimentally investigated under uniaxial cyclic loading. The effects of mean stress, stress amplitude and stress ratio on the low cycle fatigue life and ratcheting strain were discussed. It was found that the ratcheting strain increased while the fatigue life decreased with the increase of mean stress and stress amplitude, and the increasing stress ratio would result in smaller ratcheting and larger fatigue life. Two kinds of failure modes, i.e. low cycle fatigue failure due to crack propagates and ratcheting failure due to large plastic strain will take place respectively. Based on the experimental results, considered the effect of ratcheting on fatigue life, a model with the maximum stress and ratcheting strain rate was proposed. Comparison with the experimental result showed that the new model provided a good prediction for AH32 steel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.4_1
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• pp.23-32
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• 1992

The objective of this study is to identify the quantitative relationships among the important physical factors associated with failure of steel members under strong seismic excitations through very low-cycle fatigue tests. Very low-cycle fatigue is meant to be structural fatigue causing cracks and rupture in about 5~30 cycle ranges. The angle specimen was subjected to repeated axial Ioad after undergoing inelastic buckling. The test results reveal that the energy absorption capacities vary heavily with the history of loading and the failure mode. The maximum values of residual local strain at the initiation of a visible crack due to the very low-cycle fatigue were of the order of 25~40%, regardless of loading patterns, deflection modes, and width-to-thickness ratios.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.77-80
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• 2008

Low-cycle fatigue (LCF) tests were carried out to investigate the effect of loading direction on the cyclic deformation behavior and fatigue resistance of rolled AZ31 magnesium alloy. The as-received alloy showed a strong basal texture indicating that the most of basal planes of hexagonal close-packed structure were located parallel to the rolling direction. Two types of specimens whose loading directions were oriented parallel (RD) and vertical (ND) to the rolling direction. respectively, were used for the comparison. It was found that RD specimens yielded at much lower stresses during compression, while vice versa for the ND specimens, which was mainly attributed to the formation of primary twins. This anisotropic deformation behavior resulted in the different mean stresses during the cycling of RD and ND specimens, affecting the fatigue resistance of two specimens. The ND specimen showed a superior fatigue resistance as compared to the RD specimen under strain-controlled condition.

• Steel and Composite Structures
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• v.26 no.4
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• pp.439-452
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• 2018

This paper presents experimental and numerical study on buckling behaviors and hysteretic performance of Class 1 H-shaped steel beam subjected to cyclic pure bending within the scope of ultra-low cycle fatigue (ULCF). A loading device was designed to achieve the pure bending loading condition and 4 H-shaped specimens with a small width-to-thickness ratio were tested under 4 different loading histories. The emphasis of this work is on the impacts induced by local buckling and subsequent ductile fracture. The experimental and numerical results indicate that the specimen failure is mainly induced by elasto-plastic local buckling, and is closely correlated with the plastic straining history. Compared with monotonic loading, the elasto-plastic local buckling can occur at a much smaller displacement amplitude due to a number of preceding plastic reversals with relative small strain amplitudes, which is mainly correlated with decreasing tangent modulus of the material under cyclic straining. Ductile fracture is found to be a secondary factor leading to deterioration of the load-carrying capacity. In addition, a new ULCF life evaluation method is proposed for the specimens using the concept of energy decomposition, where the cumulative plastic energy is classified into two categories as isotropic hardening and kinematic hardening correlated. A linear correlation between the two energies is found and formulated, which compares well with the experimental results.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.193-204
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• 1997

In order to quantify the relationships of the important physical factors relating failure to strong earthquake loading, the plastic fatigue problems for structural components under repeated loading were reviewed first. A new concept of very low cycle fatigue failure for structural components under severe cyclic excitations as in strong earthquakes was represented. Also, an experimental study was made of the very low cycle fatigue failure of structural steel elements. It was attempted to realize the ultimate failure in the course of loading repetitions of the order of several to twenty. The test specimen had a form of rectangular plate, representing a thin-plated element in a steel member as wide-flange cross section. It was subjected to uniaxial loading repeatedly, until complete failure takes place after undergoing inelastic buckling, plastic elongation and/or their combination. It was seen as a result that the state of the ultimate failure is closely related to the maximum strain at the extreme fiber in the cross section.

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.122-130
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• 1992

The effect of loading waveform on elevated temperature low-cycle fatigue crack growth behavior in a SUS 304 stainless steel have been investigated under symmetrical trangular (fast-fast), trapezoidal and asymmetrical(fast-slow, slow-fast) waveforms at 650.deg. C. It was found that the crack growth rate in fast-slow loading waveform appeared to be higher a little and the crack growth rate in slow-fast loading waveform much higer than that in fast-fast loading waveform, and difference in crack growth rate between fast-show and slow-fast waveforms nearly didn't appear in the region of da/dN>10/sup -2/ The crack growth rate in the trapezoidal loading waveform with t/sub h/=500sec appeared to be faster than that in slow(500sec)-fast(1sec). In addition, parameter modified J-integral could be considered as useful parameter for fatigue crack growth rate in all waveforms. The result obtained are as follow. da/dN=4.91*10/sup -3/ (.DELTA. J/sub c/)/sup 0.565/.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.8
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• pp.71-76
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• 2002

In this study low cycle fatigue (LCF) behavior of 12Cr steel at high temperature are described. Secondly, comparisons between predicted lives and experimental lives are made for the several sample life prediction models. Two minute hold period in either tension or compression reduce the number of cycles to failure by about a factor of two. Twenty minute hold periods in compression lead to shorter lives than 2 minute hold periods in compression. Experiments showed that life predictions from classical phenomenological models have limitations. More LCF experiments should be pursued to gain understanding of the physical damage mechanisms and to allow the development of physically-based models which can enhance the accuracy of the predictions of components. From a design point-of-view, life prediction has been judged acceptable for these particular loading conditions but extrapolations to thermo-mechanical fatigue loading, for example, require more sophisticated models including physical damage mechanisms.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1009-1015
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• 2011

In this study, in the high expansion cycle was conduced by variable valve timing system composition to close intake valve late, and in the intake air reduction on the low compression was solved by supercharging pressure. In this wise, by constituting Diesel-Atkinson cycle, this study looked into a possibility of thermal efficiency improvement. As a result, there was improvement in thermal efficiency and output in a whole range of closing timing from ABDC $40^{\circ}$ to ABDC $80^{\circ}$. However, after ABDC $70^{\circ}$ of closing timing, the thermal efficiency increase was getting smaller. As the result of the study, the optimum intake valve closing timing was about ABDC $70^{\circ}$, high loading territory of engine was more effective than low loading territory, and engine operation in middle loading territory was stable. At this time, brake thermal efficiency was 12.5% higher than ordinary engine on average.