• Steel and Composite Structures
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• 제17권2호
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• pp.185-198
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• 2014

Carbon-manganese steel A42 (French standards) is used in steam generator pipes of nuclear center and subject to low cycle fatigue (LCF) loads. In order to obtain the material LCF behavior, the tests are implemented in a hydraulic fatigue machine. The LCF plastic deformation and cyclic stress in macroscope have been influenced by the accumulated low cycle fatigue damage. The constitutive kinematic and isotropic hardening modeling is modified with coupling fatigue damage to describe the fatigue behavior. The improved model seems to be good agreement with the test results.

• Transactions of the Korean Society of Automotive Engineers
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• 제24권5호
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• pp.504-511
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• 2016

This study investigates the durability of strut bar at car through structural and fatigue analyses. In this study, there are model 1 and model 2 as the analysis subjects. Model 1 is the existed one and model 2 is the improved one added with the reinforced part. Model 1 has the maximum equivalent stress of 165.11 MPa shown intensively at the welding part between the bracket and the bar. This stress is distributed over at the part of model 2 reinforced with this part. In case of fatigue analysis, there are three kinds of fatigue load as SAE bracket history, SAE transmission and sample history. The maximum fatigue life at SAE bracket history among three kinds of fatigue loads has the least value of $3.3693{\times}10^5$ cycles. The maximum fatigue life of model 2 becomes longer than that of model 1. As model 2 has the fatigue damage less than model 1, model 2 has the safety than model 1. As the fatigue durability about the configuration of strut bar is analyzed, it is thought to apply this study result into the real part effectively.

• Journal of Ocean Engineering and Technology
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• 제33권1호
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• pp.33-41
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• 2019

Estimating fatigue damage is a very important issue in the design of ships. The springing and whipping response, which is the hydro-elastic response of the ship, can increase the fatigue damage of the ship. So, these phenomena should be considered in the design stage. However, the current studies on the the application of springing and whipping responses at the design stage are not sufficient. So, in this study, a prediction method was developed using fluid-structural interaction analysis to assess of the fatigue damage induced by springing and whipping. The stress transfer function (Stress RAO) was obtained by using the 3D FE model in the frequency domain, and the fatigue damage, including linear springing, was estimated by using the wide band damage model. We also used the 1D beam model to develop a method to estimate the fatigue damage, including nonlinear springing and whipping by the vertical bending moment in the short-term sea state. This method can be applied to structural members where fatigue strength is weak to vertical bending moments, such as longitudinal stiffeners. The methodology we developed was applied to 325K VLOC, and we analyzed the effect of the springing and whipping phenomena on the existing design.

• Journal of Ocean Engineering and Technology
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• 제27권5호
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• pp.63-69
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• 2013

The mooring lines of a floating type offshore plant are known to show wide banded and bimodal responses. These phenomena come from a combination of low and high frequency random load components, which are derived from the drift-restoring motion characteristic and wind- sea, respectively. In this study, fatigue models were applied to predict the fatigue damage of mooring lines under those loads, and the result were compared. For this purpose, seven different fatigue damage prediction models were reviewed, including mathematical formula. A FPSO (floating, production, storage, and offloading) with a $4{\times}4$ spread catenary mooring system was selected as a numerical model, which was already installed at an offshore area of West Africa. Four load cases with different combinations of wave and wind spectra were considered, and the fatigue damage to each mooring line was estimated. The rain flow fatigue damage for the time process of the mooring tension response was compared with the results estimated by all the fatigue damage prediction models. The results showed that both Benasciutti-Tovo and JB models could most accurately predict wide banded bimodal fatigue damage to a mooring system.

• Proceedings of the Korean Reliability Society Conference
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• 한국신뢰성학회 2000년도 춘계학술대회 발표논문집
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• pp.213-222
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• 2000

In present study, a stochastic model is developed for the low cycle fatigue life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. In the proposed model, fatigue phenomenon is considered as a Markov process, and damage vector and reliability are defined on every plane. Any low cycle fatigue damage evaluating method can be included in the proposed model. The model enables calculation of statistical reliability and crack initiation direction under variable multiaxial loading, which are generally not available. In present study, a critical plane method proposed by Kandil et al., maximum tensile strain range, and von Mises equivalent strain range are used to calculate fatigue damage. When the critical plane method is chosen, the effect of multiple critical planes is also included in the proposed model. Maximum tensile strain and von Mises strain methods are used for the demonstration of the generality of the proposed model. The material properties and the stochastic model parameters are obtained from uniaxial tests only. The stochastic model made of the parameters obtained from the uniaxial tests is applied to the life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. The predicted results show good accordance with experimental results.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제12권1호
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• pp.1-8
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• 2013

This study investigates life and damage due to structural and fatigue load at speaker placer with wall hanger type. As the small stress and deformation are shown at the models of A, B and C shapes on structural analysis, there is no problem at installing speaker placer. As the largest stress is happened at the middle part of joint on the models of A, B and C shapes, this part must be considered at the design. A shape is thought to have most fatigue damage among 3 shape models. C shape model has most excellent, but A model has least at fatigue durability. This study result is applied with the design of speaker placer and it can be useful at predicting prevention and durability against its damage.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• 제21권1호
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• pp.51-57
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• 2012

This study investigates structural and fatigue analyses at bicycle pedal. Maximum deformation at model 1 is 2 times as much as model 2 at static analysis. Models 1 and 2 have the possibility of the weakest strength at the part of contact with chain gear. Among the cases of nonuniform fatigue loads at Models 1 and 2, 'SAE bracket history' with the severest change of load becomes most unstable but 'Sample history' becomes most stable. In case of 'Sample history' with the average stress of 0 to $-10^4$ MPa and the amplitude stress of 0 to $10^4$ MPa, the possibility of maximum damage becomes 4%. This stress state can be shown with 5 to 7 times more than the damage possibility of 'SAE bracket history' or 'SAE transmission'. The analysis result of this study can be effectively utilized with the safe design of pedal.

• Structural Engineering and Mechanics
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• 제50권2호
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• pp.231-240
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• 2014

In the present research, fatigue behavior of chopped strand mat/epoxy composites has been studied with two different techniques. First, the normalized stiffness degradation approach as a well-known model for unidirectional and laminated composites was utilized to predict the fatigue behavior of chopped strand mat/epoxy composites. Then, the capability of the fatigue damage accumulation model for chopped strand mat/epoxy composites was investigated. A series of tests has been performed at different stress levels to evaluate both models with the obtained results. The results of evaluation indicate a better correlation of the normalized stiffness degradation technique with experimental results in comparison with the fatigue damage accumulation model.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.355-365
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• 2020

In this study, considering the hydroelastic response represented by the springing and whipping phenomena, we propose a method of estimating the fatigue damage in the longitudinal connections of ships. First, we screened the design sea states using a load transfer function based on the frequency domain. We then conducted a time domain fluid-structure interaction (FSI) analysis using WISH-FLEX, an in-house code based on the weakly nonlinear approach. To obtain an effective and robust analytical result of the hydroelastic response, we also conducted an experimental model test with a 1/50-scale backbone-based model of a ship, and compared the experimental results with those obtained from the FSI analysis. Then, by combining the results obtained from the hydroelastic response with those obtained from the numerical fatigue analysis, we developed a fatigue damage estimation method. Finally, to demonstrate the effectiveness of the developed method, we evaluated the fatigue strength for the longitudinal connections of the real ship and compared it with the results obtained from the model tests.

• Journal of the Korean Society of Manufacturing Process Engineers
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• 제14권2호
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• pp.44-50
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• 2015

This study investigated the durability of the under bar of a car through structural and fatigue analysis. Model 1 had the lowest value among three kinds of models. In the case of the maximum equivalent stress and displacement at structural analysis, model 1 showed the highest durability. Also, models 3 and 2 showed structural durability in order of this value. In the case of fatigue analysis, the maximum fatigue lives of the three models were equal to $2{\times}10^7$cycles. However, model 1 showed the highest value among the three models, as the minimum fatigue life of model 1 becames 92.56 cycles. Also models 3 and 2 showed fatigue durability in order of this value. The maximum possibility of fatigue damage for models1,2,and 3 became 30%. If the results of this study are applied to change the design shape of the under bar of cars, the ride comfort for automobile passengers and car durability can be improved.