• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.669-678
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• 2008

The fatigue life of ship structure under cyclic loading condition is made up of initiation and propagation stages. In this study, crack growth test is carried out on large scale structure test specimens and fracture mechanical analysis is performed. The fatigue lives measured from fatigue tests are compared with DNV, Matsuoka and BS 5400 S-N curve. And to predict the crack initiation life, S-N curve, corresponding to crack length 20mm at welded joint, is developed based on hot spot stress range. Also crack propagation life is calculated using crack growth equation. Consequently, computed crack propagation life is compared with experiment results.

• Coupled systems mechanics
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• v.12 no.2
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• pp.183-197
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• 2023

Scarce research has been published on crack propagation fracture of flywheels manufactured with carbon fiber-reinforced polymers. The present work deals with a calculation method to determine the conditions for which a crack propagates in the axial direction of the flywheel. The assumptions are: flywheels made with just a single thick ply or ply clustering laminates, oriented following the hoop direction; a single crack is analyzed in the plane defined by the hoop and axial directions; the crack starts close to one of the free edges; its axial length is initially large enough so that its tip is far away from that free edge, and the crack expands the entire circumferential perimeter and keeps its concentric position. The developed method provides information for a good design of flywheels. It is concluded that a fracture-based crack propagation criterion generally occurs at a lower speed than a stress-based criterion. Also, that the evolution of failure with thickness using the fracture criterion is exponential, demonstrating that thin flywheels are relatively not sensitive to crack propagation, whereas thick ones are very prone.

• Journal of Advanced Marine Engineering and Technology
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• v.8 no.1
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• pp.49-63
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• 1984

The 5086-H116 Al-Alloy plate specimens having an edge through-thickness notch were investigated to find out the characteristics of the corner crack propagation by the plane bending fatigue. The experiments were also carried out in order to clarify the change of the corner crack propagation behaviour due to the various materials and their thicknesses. In addition, the retardation effect of overload on the corner crack propagation was quantatively studied. Main results obtained are as follows; 1. In the case of estimating the crack propagation rate of the corner crack, it is more reasonable to consider the growth rate of fracture surface area than that of crack length. 2. The shape of the corner crack growing in the plane plate under the bending fatigue can be estimated. 3. The crack propagation rate increases with the increasing of the thickness and the decreasing of the Young's modulus of materials. 4. Regardless of a thickness and kind of materials of specimen, the characteristics of the corner crack propagation can be concluded. 5. The retardation effect of overload is distinct in the corner crack propagation.

• Journal of the Korean Society of Safety
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• v.28 no.1
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• pp.12-17
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• 2013

Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was exposed for the blade safety. Plain woven CFRP instead of GFRP was inserted into the layer of the box spar for improving the strength and blade life. DCB(Double Cantilever Beam) specimen was used for evaluating fracture toughness and damage evaluation of interlaminar delamination. The material used in the experiment is a commercial material known as CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.) and UD glass fiber prepreg(Hyundai Fiber Co.). From the results, crack growth rate is not so different according to the variation of the initial crack length. Mode I interlamainar fracture toughness of fiber direction $0^{\circ}$ is higher than that of $45^{\circ}$. Interlaminar fracture has an effect on fiber direction and K decreased with lower value according to increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness is under the mixed mode loading condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode.

• Computers and Concrete
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• v.8 no.3
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• pp.343-355
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• 2011

This paper presented the model to predict the chloride diffusion coefficient in tension zone of plain concrete under flexural cyclic load. The fictitious crack based analytical model was used together with the stress degradation law in cracked zone to predict crack growth of plain concrete beams under flexural cyclic load. Then, under cyclic load, the chloride diffusion, in the steady state and one dimensional regime, through the tension zone of the plain concrete beam, in which microcracks were formed by a large number of cycles, was simulated with assumptions of continuously straight crack and uniform-size crack. The numerical analysis in terms of the chloride diffusion coefficient, $D_{tot}$, normalized $D_{tot}$, crack width and crack length was issued as a function of the load cycle, N, and load level, SR. The nonlinear model as regarding with the chloride diffusion coefficient in tension zone and the load level was proposed. According to this model, the chloride diffusion increases with increasing load level. The predictions using model fit well with experimental data when we adopted suitable crack density and tortuosity parameter.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.2
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• pp.204-212
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• 1990

The SMC composite, now being considered in certain structural applications, is anticipated to experience repeated loading during service. Thus, understanding of the fatigue behavior is essential in proper use of the composite material. In this paper, using the SMC composite composed of E-glass chopped strand and unsaturated polyester resin three point bending fatigue tests are carried out to investigate the fatigue crack propagating behavior under various cyclic stresses and fatigue damage of various microcrack forms. The following results are obtained from this study; 1) Most of the total fatigue life of the SMC composite is consumed at the initial extension or the growth of the macroscopic crack. 2) A Paris' type power-law relationship between the crack propagation rate and stress intensity factor range is obtained, and the value of material constant m is much higher (m=9~11)than that of other metals. 3) In case of high cyclic stress the fatigue damage show high microcrack density and short crack length, but in case of low cyclic stress does it vice versa. 4) Fatigue damage is characterized by microcrack density, crack length and distribution of crack orientation.

• International journal of steel structures
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• v.18 no.4
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• pp.1098-1106
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• 2018

The object of this study is to clarify fatigue limit and fatigue crack growth characteristic of SBHS700 base metal which is 780 MPa class steel. This study carried out the fatigue tests of SBHS700 base metal containing different defect size, and the fatigue limit was compared with that of the conventional steel. Test results indicate that the fatigue limit increased with decrease initial defect size, and can be precisely evaluated by using ${\sqrt{area}}$ parameter model. This paper also presents that crack growth characteristic was almost the same as that of the conventional steel from the observation of striations by using Scanning electron microscope and length of beach marks.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.3
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• pp.267-275
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• 2012

In this study, crack growth in a center-cracked plate is predicted under mode I variable amplitude loading, and the result is validated by experiment. Huang's model is employed to describe crack growth with acceleration and retardation due to the variable loading effect. Experiment is conducted with Al6016-T6 plate, in which the load is applied, and crack length is measured periodically. Particle Filter algorithm, which is based on the Bayesian approach, is used to estimate model parameters from the experimental data, and predict the crack growth of the future in the probabilistic way. The prediction is validated by the run-to-failure results, from which it is observed that the method predicts well the unique behavior of crack retardation and the more data are used, the closer prediction we get to the actual run-to-failure data.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.471-472
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• 2009

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.1
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• pp.14-21
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• 2002

The development of a new experimental method is required to easily observe the growth behavior of fatigue cracks. To satisfy the requirement, an image processing technique was introduced to fatigue testing. The length of surface fatigue crack could be successfully measured by the image processing system. At first, the image data of cracks were stored into the computer while the cyclic loading was interrupted. After testing, crack length was determined using an image processing software which was developed by authors. Various image processing techniques like a block matching method was applied tc the detection of surface fatigue cracks. By comparing the data measured by the image processing system with those by the manual measurement with a microscope, the effectiveness of the image processing system was established. If the proposed method is used to monitor and observe the crack growth behavior automatically, the time and efforts for fatigue test could be dramatically reduced.