• Journal of Advanced Marine Engineering and Technology
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• v.21 no.5
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• pp.542-548
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• 1997

In this study an evaluation method of fatigue strength of membrane type LNG tank is presented with FEM analysis and experimental approach of seam and raised edge welds. The study contains the following : l)FEM analysis of test specimens 2)Fatigue tests of seam and raised edge welds 3)Estimation of cumulative damage factor of the welds on the basis of safe life design concept complying with the rules of classification society 4)Review of the effect of mean stress on the fatigue strength 5)Modelling of fatigue life of the welds which is changeable by weld heights With the results obtained in this study, a model ${\Delta}{\delta}/h^2=0.13553\;{N_{f}}^{-0.3151}$ for seam and raised edge welds having a given weld height is proposed to be useful for designers and inspectors.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.923-928
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• 2005

The estimation of fatigue life at the design stage of the compressed air tank on board is very important in order to arrive at feasible and reliable solutions considering the total lifetime of the tank. In this paper the compressed air tank on board was selected as a model and the change of inside pressure of the tank during normal navigation period was measured and the cycle of fluctuation stress was presumed statistically based on this. Also the effect of stress concentration with the FEM analysis on the longitudinal weld and the mean stress effect on the fatigue strength of compressed air tank were discussed.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.7
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• pp.1131-1137
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• 2004

Recently there has been a remarkable increase in the number of high speed and large ships and the high power involved for propulsion of above ships has brought high pitch ratio and highly skewed propeller. The recent tendency toward highly skewed propeller has increased the load on propeller blades, and the fatigue strength of propeller blades has become the critical point in design of propellers for ships. In this paper the effect of stress ratio and skew angle on the fatigue strength of highly skewed propeller, the statistical inference on the total revolutions of highly skewed propeller for 20 years under normal sea going state. and so on have been discussed. On the basis of above discussions, the highly skewed propeller blade thicknesses by the rules of classification society and the standards of manufacturer in country were compared and reviewed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.581-584
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• 2005

A district heating(DH) system supplies environmentally-friend heat and is appropriate for reduction of energy consumption and/or air pollutions. The objectives of this paper are to systematize data processing of transition temperature, investigate its effects on fatigue life of DH pipes and optimization for size of DH pipes. A relational database management system as well as reliable fatigue life evaluation procedures is established for Korean DH pipes. Also, since the prototypal evaluation results satisfied both cycle-based and stress-based fatigue criteria. Through the optimum design process, the cross section diminished 18.64% and the CUF diminished 23.35%. So, it can be used as useful information in the future for optimal design, operation and energy saving via setting of efficient condition and stabilization of water temperature.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1667-1674
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• 2010

The fatigue life is estimated while determining the reliability of aircraft structures. In this study, the estimation of fatigue life was carried out on the basis of a cumulative damage theory; the working S-N curve and the equivalent stress on the engine support structure significantly affect the safety of the aircraft. The maximum stress observed was 1,080 MPa in the case of scissors link under crash load condition, and there was a 5% margin for the allowable stress corresponding to the temperature reduction factor. The maximum stress was 876 MPa, and the stress equation coefficient had a maximum value of 0.019 MPa/N in the case of scissors link under fatigue loads. In the results of the fatigue life analysis, the safety life in a fretting area of scissors link upper part was 416,667 flight hour, and other parts showed to infinite life. Therefore, it was demonstrated that the fatigue life requirement of aircraft engine support structure (scissors link, straight link) could be satisfied.

• Journal of Sensor Science and Technology
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• v.5 no.6
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• pp.15-24
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• 1996

In this study, as a part of the basic study for the application of optical fiber sensors to smart composite structures, the integrity of optical fiber sensors embedded within the composite structures was examined and then the laser signal transmitted through optical fiber sensors during the deformation of host structures was investigated. Firstly, it was found that bending test could be substituted for tensile test by comparing cumulative failure distribution based on weakest link theory and introducing the correction factor. Weibull parameters were obtained through the experiments and the correction factor was found to be applied to cumulative failure distribution derived from bending test. The integrity of embedded optical fiber sensors due to the thermal effect was evaluated by the comparison of the mean tensile strengths of cured and uncured optical fibers. Secondly, relationships between stress-strain curve obtained in tensile test of composite laminate and the intensity of laser signal transmitted through embedded optical fibers were examined and the possibility of the effective damage detection using optical fiber sensors was studied.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.112-124
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• 1993

It has been reported that fatigue damage sometimes occurred at the stress concentrated and dynamic loaded structural members of bulk carrier. In this paper, studies on fatigue strength of hull structures are reviewed, and the program for evaluating fatigue strength is developed. And the fatigue crack initiation and propagation on the end part of cargo hold frame of bulk carrier were calculated by FEM stress analysis and the fatigue strength evaluation program. These method can be applied not only to the crack initiation life but also to crack propagation life for the hull structural members at the hull design stage and be effective as the guideline to prevent the crack initiation or to estimate the fatigue strength for repairing of the fatigue damaged structures of real ships.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.6 s.183
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• pp.143-150
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• 2006

Recently, in proportion to increased demand on environmentally-friendly heat source, efficient management of district heating(DH) system becomes one of important issue. The objectives of this paper are to systematize data processing of transition temperature, investigate the effect of temperature variations on thermal fatigue and find out a way to improve design fractures of Korean DH pipes. For this purpose, reliable fatigue lift evaluation procedures are examined and applied to quantify thermal fatigue lives. Also, as a prototypal optimization analysis results, mean value of original cross sectional area of selected pipes was reduced 18.6% sustaining their sufficient margins against fatigue failure. So, it is anticipated that the output of this research can be used as useful information of optimal design and operation in the future.

• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.126-132
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• 2023

Recently, the consideration of eco-friendly technology to reduce greenhouse gas is being emphasized in the aviation field. Various studies for applying electro-mechanical actuators that control mechanical linear and rotational movements using electricity as the primary power source are in progress. In this study, the fatigue analysis of the electro-mechanical actuator for the front wheel steering of a single aisle aircraft was carried out. A unit load stress table was constructed for the vulnerable part selected through structural analysis, and the representative stress for each load profile was calculated using the unit load stress table constructed for the vulnerable part. Then, individual profiles of representative stress group were extracted from continuous load profiles by applying the rainflow counting method. The damage of each profile was calculated by applying the S-N diagram. Finally, the total damage in the vulnerable parts was calculated by the linear cumulative damage law, and the fatigue life of the electro-mechanical actuator for the front wheel steering of a single aisle aircraft was evaluated.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.453-461
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• 1999

The estimation of fatigue life at the design stage is very important in order to arrive at feasible and cost effective solutions considering the total lifetime of the structure and machinery compo-nents. In this study the practical procedure of prediction of fatigue life by use of cumulative damage factors based on Miner-Palmgren hypothesis and probability density function is shown with a $135,000m^3$ LNG tank being used as an example. In particular the parameters of Weibull distribution taht determine the stress spectrum are dis-cussed. At the end some of uncertainties associated with fatigue life prediction are discussed. The main results obtained from this study are as follows: 1. The practical procedure of prediction of fatigue life by use of cumulative damage factors expressed in combination of probability density function and S-N data is proposed. 2. The calculated fatigue life is influenced by the shape parameter and stress block. The conser-vative fatigue design can be achieved when using higher value of shape parameter and the stress blocks divded into more stress blocks.