• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.7
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• pp.1713-1721
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• 1994

Intermetallic-matrix composites(IMCs) have the potential of combing matrix properties of oxidation resistance and high temperature stability with reinforcement properties of high specific strength and modulus. One of the major limiting factors for successful applications of these composite at high temperatures is the formation of interfacial reactions between matrix and ceramic reinforcement during composite process and during service. The purpose of the present investigation is to develop a better understanding of the nature of creep fracture mechanisms in a $Ni_{3}Al$ composite reinforced with both $TiB_{2}$ and SiC particulates. Emphasis is placed in the roles of the products of the reactions in determining the creep lifetime of the composite. In the present study, creep rupture specimens were tested under constant ranging from 180 to 350 MPa in vacuum at $760^{\cric}C$. The experimental data reveal that the stress exponent for power law creep for the composite is 3.5, a value close to that for unreinforced $Ni_{3}Al$. The microstructural observations reveal that most of the cavities lie on the grain boundaries of the $Ni_{3}Al$ matrix as opposed to the large $TiB_{2}/Ni_{3}Al$ interfaces, suggesting that cavities nucleate at fine carbides that lie in the $Ni_{3}Al$ grain boundaries as a result of the decomposition of the $SiC_{p}$. This observation accounts for the longer rupture times for the monolicthic $Ni_{3}Al$ as compared to those for the $Ni_{3}Al/SiC_{p}/TiB_{2} IMC$. Finally, it is suggested that creep deformation in matrix appears to dominate the rupture process for monolithic $Ni_{3}Al$, whereas growth and coalescence of cavities appears to dominate the rupture process for the composite.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.435-443
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• 2015

Offshore structure may be considerably vulnerable to fatigue failure while initial flaw propagates under cyclic loading, so crack propagation analysis/fracture/yield assessments about initial flaw detected by NDT are necessarily required. In this paper, case studies have been conducted by flaw assessment program using engineering criticality analysis (ECA) approach. Variables such as flaw geometry, flaw size, structure geometry, dynamic stress, static stress, toughness, crack growth rate, stress concentration factor (SCF) affected by weld are considered as analysis conditions. As a result, the safety of structure was examined during fatigue loading life. Also, critical initial flaw size was calculated by sensitivity module in the developed program. The flaw assessments analysis using ECA approach can be very useful in offshore industries owing to the increasing demand on the engineering criticality analysis of potential initial flaws.

• Journal of the Korean Wood Science and Technology
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• v.39 no.5
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• pp.451-458
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• 2011

Adhesives derived from renewable resources allow wood panel producers to make lower cost alternatives to formaldehyde-based adhesive resins. Among them, adhesive components extracted from industrial by-products or wastes are the most important research fields in the efficient utilization of waste and cost reduction. In our study, the rapeseed flour, which is a by product from the production of biodiesel extracted from rapeseed, was introduced to develop alternative adhesives for the production of wood flooring. The rapeseed flour was hydrolyzed with 1% sodium hydroxide solution and PF prepolymers were prepared with 3-molar ratios, 1.8, 2.1 and 2.4. The linear fracture mechanics was introduced to evaluate the glue bond quality in wood flooring composed of fancy-veneered and plywood, and the formaldehyde emission and adhesive penetration were also investigated. The formaldehyde emissions of wood flooring met the requirement of the standard of $SE_0$ specified in the KS standard. The rapeseed flour adhesive penetrated sufficiently into the vessel elements and lumens in fancy veneer and plywood and gave strong bond quality to the wood flooring. The fracture mechanics was introduced to evaluate the adhesive joint between fancy veneer and plywood. The critical stress intensity factor ($K_{IC}$) of boliva overlayed wood flooring was increased with increasing molar ratio and this was the same tendency in oak overlayed wood flooring. From the results, the formulated adhesives were efficiently used to bond fancy veneer onto the plywood to make wood flooring and showed a potential to be used as a component of environmentally friendly adhesive resin systems for production of flooring.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.3 no.4
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• pp.341-348
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• 2005

Bentonite has been considered as a candidate buffer material in the underground repository for the disposal of high-level radioactive waste because of its low permeability, high sorption capacity, self sealing characteristics, and durability in nature. In this study, the potential for separation of bentonite particles caused by the groundwater erosion was studied experimentally for a Korean Ca-bentonite under the relevant repository conditions. Results showed that bentonite particles can be generated at the bentonite/granite interface and mobilized by the water flow although the intrusion of bentonite into fracture by swelling pressure was observed to be small. Different processes of mobilization of theses colloids from the compacted bentonite block have been identified in this study. The concentration of particles eluted in water was increased as the flow rate increased. Thus the result reveals that the erosion of the bentonite surface due to the groundwater flow together with intrusion processes is the main mechanism that can mobilize bentonite colloids in the fracture of the granite.

• Structural Engineering and Mechanics
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• v.22 no.2
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• pp.169-184
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• 2006

A close form solution of the maximum deflection for cracked columns with rectangular cross-sections was developed and thus the elastic buckling behavior and ultimate bearing capacity were studied analytically. First, taking into account the effect of the crack in the potential energy of elastic systems, a trigonometric series solution for the elastic deflection equation of an arbitrary crack position was derived by use of the Rayleigh-Ritz energy method and an analytical expression of the maximum deflection was obtained. By comparison with the rotational spring model (Okamura et al. 1969) and the equivalent stiffness method (Sinha et al. 2002), the advantages of the present solution are that there are few assumed conditions and the effect of axial compression on crack closure was considered. Second, based on the above solutions, the equilibrium paths of the elastic buckling were analytically described for cracked columns subjected to both axial and eccentric compressive load. Finally, as examples, the influence of crack depth, load eccentricity and column slenderness on the elastic buckling behavior was investigated in the case of a rectangular column with a single-edge crack. The relationship of the load capacity of the column with respect to crack depth and eccentricity or slenderness was also illustrated. The analytical and numerical results from the examples show that there are three kinds of collapse mechanisms for the various states of cracking, eccentricity and slenderness. These are the bifurcation for axial compression, the limit point instability for the condition of the deeper crack and lighter eccentricity and the fracture for higher eccentricity. As a result, the conception of critical transition eccentricity $(e/h)_c$, from limit-point buckling to fracture failure, was proposed and the critical values of $(e/h)_c$ were numerically determined for various eccentricities, crack depths and slenderness.

• Journal of Preventive Medicine and Public Health
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• v.35 no.4
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• pp.305-312
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• 2002

Objectives : The reproductive history of women has been suggested to have a possible influence on the risk of osteoporotic fractures. The purpose of this study was to assess the association between reproductive history and hip fractures in the elderly women. Methods : The study subjects were drawn from women members of the Korean Elderly Pharmacoepidemiologic Cohort (KEPEC), aged 65 years or over, whose reproductive histories were available, and who were beneficiaries of the Korea Medical Insurance Corporation (KMIC) in 1993 and lived in Busan city, Korea. The information on reproductive histories, and possible confounders, were collected from mailed questionnaires. Potential hip fracture cases were collected from the claims data obtained between 1993 and 1998, with a hospital survey conducted to confirm the final diagnoses. Rate ratios and their 95% confidence intervals, were calculated using a Cox's proportional hazard model. Results : Following up 5,215 women for 6 years, 51 cases were confirmed with hip fractures. When adjusted for age, weight and physical activity, the rate ratio of hip fractures in women who had given birth three or more times was 0.56 (95% CI: 0.25-1.25), compared with those who had given birth two or less times. When adjusted for age, number of births, weight and physical activity, the rate ratio in women who first gave birth when younger than 22 years was 0.60 (95% CI: 0.34-1.08) compared with those who had giving birth at 22 years or older. Conclusions : According to these findings, an early age when first giving birth might decrease the risk of hip fractures in elderly Korean women.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.19 no.1
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• pp.79-84
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• 1983

The test specimen, designated the double cantilever beam, was employed for a fracture mechanics study of stress corrosion cracking (SCC) of type 5083 Al-alloy in seawater. Stress intensities for this DCB specimen were calculated by using compliance, strain energy release rate and relation between stress intensity and strain energy release rate. Analytical expression for compliance as a function of crack length was obtained by applying beam theory. It was investigated that the polarization potentials affected the growth rate and surface of stress corrosion cracking. The results are as follows, The critical stress intensity was 134.81-148.38kg/mm super(3/2) and K sub(Ii) under polarization potentials was 75.92-145.78kg/mm super(3/2). The minimum stress corrosion crack growth rate was occurred at-987mV SCE. Insoluble compound on $\beta$ phase was looked into through SCC. The greater anodic potential is, the larger insoluble compound on $\beta$ phase becomes.

• Textile Coloration and Finishing
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• v.30 no.4
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• pp.313-320
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• 2018

As carbon fiber reinforced composites(CFRP) are widely used in aerospace, automobile, marine, and sports goods applications, they have been studied extensively by various researchers. However, CFRP have been pointed out because of machining problems such as delamination and burr phenomenons. Especially, hole machining process, drilling, has non-smooth features on inlet and outlet surfaces of drilled hole. This kind of machining problem can be controlled to some extent by using high modulus pitch-CF, which has considerable effects on fracture behavior of composite compared with only PAN CF composite. Therefore, PAN and pitch hybridized CF composites were prepared having high strength and modulus. The results demonstrate that the hybrid CFRP specimens with pitch CF offer the good potential to enhance modulus as well as strength properties. Dynamic mechanical, flexural, and impact properties were measured and analyzed. Morphological surface of the composites were also observed by IFS-28, canon after hole machining.

• Geomechanics and Engineering
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• v.33 no.5
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• pp.477-486
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• 2023

In the studies on fault dislocation of tunnel, existing literatures are mainly focused on the problems caused by normal and reverse faults, but few on strike-slip faults. The paper aims to research the deformation and failure mechanism of a tunnel under strike-slip faulting based on a model test and test-calibrated numerical simulation. A potential faulting hazard condition is considered for a real water tunnel in central Yunnan, China. Based on the faulting hazard to tunnel, laboratory model tests were conducted with a test apparatus that specially designed for strike-slip faults. Then, to verify the results obtained from the model test, a finite element model was built. By comparison, the numerical results agree with tested ones well. The results indicated that most of the shear deformation and damage would appear within fault fracture zone. The tunnel exhibited a horizontal S-shaped deformation profile under strike-slip faulting. The side walls of the tunnel mainly experience tension and compression strain state, while the roof and floor of the tunnel would be in a shear state. Circular cracks on tunnel near fault fracture zone were more significant owing to shear effects of strike-slip faulting, while the longitudinal cracks occurred at the hanging wall.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.529-536
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• 2008

The failure behavior of structures is changed under different loading rates, which might arise from the rate dependency of materials. This phenomenon has been focused in the engineering fields. However, the failure mechanism is not fully understood yet, so that it is hard to be implemented in numerical simulations. In this study, the numerical experiments to a brittle material are simulated by the Molecular Dynamics (MD) for understanding the rate dependent failure behavior. The material specimen with a notch is modeled for the compact tension test simulation. Lennard-Jones potential is used to describe the properties of a brittle material. Several dynamic failure features under 6 different loading rates are achieved from the numerical experiments, where remarkable characteristics such as crack roughness, crack recession/arrest, and crack branching are observed during the crack propagation. These observations are interpreted by the energy inflow-consumption rates. This study will provides insight about the dynamic failure mechanism under different loading rates. In addition, the applicability of the MD to the macroscopic mechanics is estimated by simulating the previous experimental research.