• Journal of Korean Society of Steel Construction
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• v.15 no.5 s.66
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• pp.475-487
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• 2003

This study developed an analysis model of estimating fatigue damage using the linear elastic fracture mechanics method. Stress history occurring to an element when a truck passed over a bridge was defined as block loading and crack closure theory explaining load interaction effect was applied. Stress range frequency analysis considering dead load stress and crack opening was done. Probability of stress range frequency distribution was applied and the probability distribution parameters were estimated. The Monte Carlo simulation of generating the probability various of distribution was performed. The probability distribution of failure block numbers was obtained. With this the fatigue reliability of an element not occurring in failure could be calculated. The failure block number divided by average daily truck traffic remains the life of a day. Fatigue reliability analysis model was carried out for the welding member of cross beam flange and vertical stiffener of steel box bridge using the proposed model. Consequently, a 3.8% difference was observed between the remaining life in the peak analysis method and in the proposed analysis model. The proposed analysis model considered crack closure phase and crack retard.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.83-84
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• 2007

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.4
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• pp.438-452
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• 2005

Statement of problem: The use of Ceromer is increasing in dentistry. But, the research of Ceromer has not been conducted much. Purpose : This study was to evaluate the marginal fidelity and internal adaptation according to marginal position. Materials and Methods: In this study 60 resin crowns were fabricated. The measurements of the marginal fidelity were carried out using stereomicroscope $SZ-40^{(R)}$ (Olympus, Japan) and the measurements of fracture strength were done using Instron $8871^{(R)}$ (Instron Co., U.S.A.) at a cross head speed of 1mm/min. All of the measurements were statistically analyzed by ANOVA test, multiple range test and Weibull analysis. Statistical significance was set in advance at the probability level of less than 0.05. All of the measurements were analyzed with Window $SPSS^{(R)}$ Version 10.0 soft ware for the personal computer. Results : 1. There were no statistical differences of the marginal fidelity between $Targis^{(R)}$ and $Tescera^{(R)}$, but difference between these two and $BelleGlass^{(R)}$ according to materials. 2. There were no statistical differences of the marginal fidelity between no fiber group and fiber group. There were no interactions between each maerial and with/without fiber group in the marginal fidelity 3. There were statistical differences of the fracture strength between $Tescera^{(R)}$ and $BelleGlass^{(R)}$ but no statistical differences of the fracture strength between $Targis^{(R)}$ and $Tescera^{(R)}$, $Targis^{(R)}$ and $BelleGlass^{(R)}$ according to materials. 4 There were statistical differences of the fracture strength between no fiber group and fiber group. There were no interactions between each material and with/without fiber group in the fracture strength. 5. When comparing the fracture surface, no fiber group showed the resin which were fractured at the labial surface and separated from the adhesion surface. In fiber group, the fractures took a place in resin compartments. Conclusion. The marginal fidelity and the fracture strength were clinically acceptable. From these results, $Targis^{(R)}$ and $Tescera^{(R)}$ were superior than $BelleGlass^{(R)}$ in the marginal fidelity But, when applying these resin crowns in clinic, more careful consideration is needed and further study is recommended.

• Tunnel and Underground Space
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• v.14 no.3
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• pp.167-174
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• 2004

This paper is to introduce an article published in Rock Mechanics and Rock Engineering, 2003. In this research, a fracture mechanics model is developed to illustrate the importance of time-dependence far brittle fractured rock. In particular a model is developed fer the time-dependent degradation of rock joint cohesion. Degradation of joint cohesion is modeled as the time-dependent breaking of intact patches or rock bridges along the joint surface. A fracture mechanics model is developed utilizing subcritical crack growth, which results in a closed-form solution for joint cohesion as a function of time. As an example, a rock block containing rock bridges subjected to plane sliding is analyzed. The cohesion is found to continually decrease, at first slowly and then more rapidly. At a particular value of time the cohesion reduces to value that results in slope instability. A second example is given where variations in some of the material parameters are assumed. A probabilistic slope analysis is conducted, and the probability of failure as a function of time is predicted. The probability of failure is found to increase with time, from an initial value of 5% to a value at 100 years of over 40%. These examples show the importance of being able to predict the time-dependent behavior of a rock mass containing discontinuities, even for relatively short-term rock structures.

• Journal of the Korean Society for Railway
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• v.13 no.2
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• pp.201-207
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• 2010

The replacement criterion of rail by accumulated passing tonnage was estimated by the bending fatigue life of rail. In order to estimate the bending fatigue life, it is basically needed to analyze bending fatigue behavior on the rail. In this study, the bending fatigue test were performed for 50kg/m and 60kg/m rails, and test specimens were distinguished by new and used rails and by the types of welded rail such as base material, thermite weld, and gas pressure weld. Also, this study analyzed the fractured surface, the position of initial crack and the bending fatigue behavior (S-N curve). Therefore, it evaluated S-N curve for welded rails according to the fracture probability. The result from this study might be used essential data in order to estimate the bending fatigue life of rail by the accumulated passing tonnage.

• Journal of Welding and Joining
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• v.17 no.1
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• pp.124-132
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• 1999

Thermal fatigue strength of the solder joints is the most critical issue for TSOP(Thin Small Outline Package) because the leads of this package are extremely short and thermal deformation cannot be absorbed by the deflection of the lead. And the TSOP body can be subject to early fatigue failures in thermal cycle environments. This paper was discussed distribution of thermal stresses at near the joint between silicon chip and die pad and investigated their reliability of solder joints of TSOP with 42 alloy clad lead frame on printed circuit board through FEM and 3 different thermal cycling tests. It has been found that the stress concentration around the encapsulated edge structure for internal crack between the silicon chip and Cu alloy die pad. And using 42 alloy clad, The reliability of TSOP body was improved. In case of using 42 alloy clad die pad(t=0.03mm). $$\sigma$_{VMmax}$ is 69Mpa. It is showed that 15% improvement of the strength in the TSOP body in comparison with using Cu alloy die pad $($\sigma$_{VMmax}$=81MPa). In solder joint of TSOP, the maximum equivalent plastic strain and Von Mises stress concentrate on the heel of solder fillet and crack was initiated in it's region and propagated through the interface between lead and solder. Finally, the modified Manson-Coffin equation and relationship of the ratio of $N_{f}$ to nest(η) and cumulative fracture probability(f) with respect to the deviations of the 50% fracture probability life $(N_{f 50%})$ were achieved.

• Journal of the Microelectronics and Packaging Society
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• v.18 no.1
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• pp.15-21
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• 2011

In this study, flexural strength and fracture behavior of silicon die from single crystalline silicon wafer were investigated as a function of thickness. Silicon wafers with various thickness of 300, 200, 180, 160, 150, and 100 ${\mu}m$ were prepared by mechanical grinding and polishing of as-saw wafers. Flexural strength of 40 silicon dies (size: 62.5 mm${\times}$4 mm) from each wafer was measured by four point bending test, respectively. For statistical analysis of flexural strength, shape factor(i.e., Weibull modulus) and scale factor were determined from Weibull plot. Flexural strength reflecting both statistical fracture probability and size (thickness) effect of brittle silicon die was obtained as a linear function of die thickness. Fracture appearance was discussed in relation with measured fracture strength.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.4 no.1
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• pp.9-15
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• 2006

For the accurate safety assessment of potential radioactive waste disposal site which is located in the crystalline rock it is important to simulate the mass transportation through engineered and natural barrier system precisely, characterized by porous and fractured media respectively. In this work the methods to construct discrete fracture network for the analysis of flow and mass transport through fractured-porous medium are described. The probability density function is adopted in generating fracture properties for the realistic representation of real fractured rock. In order to investigate the intersection between a porous and a fractured medium described by a 2 dimensional rectangular and a cuboid grid respectively, an additional imaginary fracture is adopted at the face of a porous medium intersected by a fracture. In order to construct large scale flow paths an effective method to find interconnected fractures and algorithms of swift detecting connectivities between fractures or porous medium and fractures are proposed. These methods are expected to contribute to the development of numerical program for the simulation of radioactive nuclide transport through fractured-porous medium from radioactive waste disposal site.

• Composites Research
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• v.22 no.2
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• pp.43-48
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• 2009

For the practical use of improved interlaminar fracture toughness by interleaving carbon non-woven tissue (CNWT), intelaminar fracture toughnesses of CFRP laminates with CNWT having different weights were experimentally investigated. A suitable weight of interleaved CNWT in CFRP laminates was discussed with Mode I and Mode II tests. Mode I and Mode II interlaminar fracture toughnesses (GIC and GIIC) were obtained by DCB and ENF tests. Six kinds of specimens with CNWT were prepared. The weights of CNWT per square meter for six types of specimens are $8g/m^2,\;10g/m^2,\;12g/m^2,\;16g/m^2,\;20g/m^2$, and $24g/m^2$, respectively. The mean GIC and GIIC values of six kinds of specimens were not substantially different from one another. Compared with the CFRP specimen, the mean GIC values of six kinds of specimens were slightly decreased. But the mean GIIC values increased tremendously at least twice by interleaving CNWT. It seems that there is no interrelationship between the interlaminar fracture toughnesses (GIC and GIIC) and the interleaving CNWT weights. Consequently, it would be desirable to use the CNWT of $8g/m^2$ among the six kinds of CNWTs to take advantage of the interlaminar fracture toughness improved by interleaving CNWT, because the CNWT of $8g/m^2$ is a lightweight and low-priced material.

• Journal of Ocean Engineering and Technology
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• v.31 no.3
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• pp.233-240
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• 2017

Subsea structures are always vulnerable to accidental risks induced by fishing gear, dropped objects, etc. This paper presents the design of a subsea manifold protective structure that protects against dropped object impacts. Probable dropped object scenarios were established considering the shapes and masses of the dropped objects. A design layout for the manifold protective structure was proposed, with detailed scantlings and material specifications. A method applicable to the pipelines specified in DNV-RP-F107(DNV, 2010) was applied to calculate the annual probabilities of dropped objects hitting the subsea manifold. Nonlinear finite element analyses provided the structural consequences due to the dropped object impacts such as the maximum deflections of the protective structure and the local fracture occurrences. A user-subroutine to implement the three-dimensional fracture strain surface was used to determine whether local fractures occur. The proposed protective structure was shown to withstand the dropped object impact loads in terms of the maximum deflections, even though local fractures could induce accelerated corrosion.