• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.9
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• pp.1357-1363
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• 1997

Currently it is increasing to use th bonded dissimilar materials in the various field of advanced engineering such as the highly rigid and lighter vehicle, plastic molding LSI package and metal/ceramic bonded joint. In spite of such a wide application of the bonded dissimilar materials, the evaluation method of the bonding strength has not been established yet. Therefore in this paper we analyze the interface crack problem by introducing fracture mechanics parameters as the basic research about estimating of the strength of adhesive joints. The variation of stress intensity factor according to the elastic modulus of adherend and thickness of bonded layer are investigated. Numerical results are based on the results of boundary element analysis of four different type butt joints subjected to uniaxial tension loading.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.38
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• pp.24.1-24.7
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• 2016

Background: This study aimed to evaluate the structural changes of temporomandibular joint immediately after condylar fractures with magnetic resonance imaging (MRI). Method: We evaluated 34 subjects of condylar fractures with MRI. The position, shape, and signal intensity of the condyle, disc, and retrodiscal tissue were analyzed with MR images. Results: Immediately after trauma, the disc was displaced with the fractured segment in almost all cases. And, the changes of signal intensity at the retrodiscal tissue were found but less related to the degree of fracture displacement. And, the high signals were observed almost at all fractured joint spaces and even at some contralateral joints. Conclusions: The displaced disc as well as the increased signal intensity of the joint space, condylar head, and retrodiscal tissue demands more attention to prevent the possible sequela of joint.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.106-111
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• 2003

This study made an experiment On fatigue crack propagation da/dn, stress intensity factor range ${\Delta}K$ respectively in room temperature and in low temperature. And we got the following characteristics from fatigue crack growth test carried Out in the environment of room temperature and law temperature at $25^{\circ}C$, $-60^{\circ}C$, $-80^{\circ}C$, and $-100^{\circ}C$ in the range of stress ratio of 0.3 by means of opening made displacement. The threshold stress intensity factor range ${\Delta}Kth$ in the early stage of fatigue crack growth (Mode I) and stress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Made II) was decreased in proportion to descend temperature. It assumed that the fatigue resistance characteristics and fracture strength at law temperature and high temperature is considerable higher than that of room temperature in the early stage and stable of fatigue crack growth region.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.104-110
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• 1987

Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.1
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• pp.100-106
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• 1993

This paper aims to synthesize the research on fatigue fracture mechanisms of high strength aluminum alloys which are widely used in motorcars or airplanes to prevent accidents. To measure the data of crack opening ratio, the same materials and method are used for evaluating the fatigue crack propagation rate as an effective stress intensity factor. But, many researchers have brought different results. An exact crack opening ratio was, therefore, proposed for getting a more accurate fatigue crack propagation rate. The main conclusions obtained are as follows. (1) As a result of the fatigue test, the value of the crack opening ratio is the same regardless of the stress ratio. (2) The value of crack opening ratio is different according to the measuring point. After measuring the crack propagation rate by using an effective stress intensity factor, the crack opening ratio value measured at the crack mouth by a clip gage, or measured rear of the specimen by a strain gage is more accurate than that by any other measuring test.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.90-99
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• 2002

The prediction of stress intensity factor(SIF) is one of the most important factors to analyse the propagation behavior of cracks in hull structural members. Up to now, however, simplified prediction method of SIF has not yet been established for the cracks experienced in large complex structures. As a first step to predict crack propagation behavior in a ship structure with very large structural redundancies, simplified SIF prediction formulas for various crack shapes were derived based on the results of the stress analysis under a non-crack condition in this study. The adequacy of the proposed method was then verified in comparison with other experimental and analysis results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.313-330
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• 1993

The propagating crack problems under dynamic plane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems in orthortropic material, it is important to know the dynamic stress components and dynamic displacement components around the crack tip. Therefore the dynamic stress components of dynamic stress field and dynamic displacement components of dynamic displacement field in the crack tip of orthotropic material under the dynamic load and the steady state in crack propagation were derived. When the crack propagation speed approachs to zero, the dynamic stress component and dynamic displacement components derived in this study are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determinded by using the concept of crack closure closure energy with the dynamic stresses and represented according to physical properties of the orthotrophic material and crack speeds. The faster the crack velocity, the greater the stress value of stress components in crack tip. The stress value of the stress component of crack tip is greater when fiber direction coincides with the crack propagation than when fider direction is normal to the crack propagation.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.286-291
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• 2001

Most cracks in the structure occur under mixed mode loadings and those propagation depend on the stress ratio very much. So, it is necessary to study the fatigue behavior under mixed mode loading as stress ratio changes. In this paper, fatigue crack propagation behavior was investigated respectively at stress ratio 0.1, 0.3, 0.5, 0.7 and we change loading application angle to $0^{\circ},\;30^{\circ},\;60^{\circ}$ to apply various loading. mode. The mode I and II stress intensity factors of CTS specimen used in this study were calculated by displacement extrapolation method using FEM(ABAQUS). Using both the study through the experiment and the theoretical study through FEM analysis, we studied the relation between crack propagation rate and stress intensity factor range at each loading mode due to the variation of stress ratio. Also, when the crack propagated under given stress condition and given loading mode condition, we studied what the dominant factors of the crack propagation rate were at each case.

• Advanced Composite Materials
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• v.16 no.4
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• pp.315-334
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• 2007

In the present study, chopped henequen natural fibers without and with surface modification by electron beam (E-beam) treatment were incorporated into a polypropylene matrix. Prior to composite fabrication, a bundle of raw henequen fibers were treated at various E-beam intensities from 10 kGy to 500 kGy. The effect of E-beam intensity on the interfacial, mechanical and thermal properties of randomly oriented henequen/polypropylene composites with the fiber contents of 40 vol% was investigated focusing on the interfacial shear strength, flexural and tensile properties, dynamic mechanical properties, thermal stability, and fracture behavior. Each characteristic of the material strongly depended on the E-beam intensity irradiated, showing an increasing or decreasing effect. The present study demonstrates that henequen fiber surfaces can be modified successfully with an appropriate dosage of electron beam and use of a low E-beam intensity of 10 kGy results in the improvement of the interfacial properties, flexural properties, tensile properties, dynamic mechanical properties and thermal stability of henequen/polypropylene composites.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.3
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• pp.353-361
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• 2001

Recently the boundary element method has been developed swiftly. The boundary element method is an efficient and accurate means for analysis of two dimensional elastic crack problems. This paper is concerned with the evaluation and the prediction of the stress intensity factor(SIF) for the crack emanating from the circular hole using boundary element method-neural network. The SIF of the crack emanating from the hole was calculated by using boundary element method. Neural network is used to evaluate and to predict SIF from the results of boundary element method. The organized neural network system (structure of four processing element) was learned with the accuracy 99%. The learned neural network system could be evaluated and predicted with the accuracy of 83.3% and 71.4% (in cases of SIF and virtual SIF). Thus the proposed boundary element method-neural network is very useful to estimate the SIF.