• Journal of the Korean Society of Safety
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• v.20 no.2 s.70
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• pp.26-31
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• 2005

The strong continuous fiber reinforced metal matrix composites (MMCs) are recently used in aerospace and transportation applications as an advanced material due to its high strength and light weight. Unidirectional fiber-metal matrix composites have superior mechanical properties along the longitudinal direction. However, the applicability of continuous fiber reinforced MMCs is somewhat limited due to their relatively poor transverse properties. Therefore, the transverse properties of MMCs are significantly influenced by the properties of the fiber/matrix interface. In order to be able to utilize these MMCs effectively and with safety, it must be determined their elastic plastic behaviors at the interface. In this study, the interfacial stress states of transversely loaded unidirectional fiber reinforced metal matrix composites investigated by using elastic-plastic finite element analysis. Different fiber volume fractions $(5-60\%)$ were studied numerically. The interlace was treated as three thin layer (with different properties) with a finite thickness between the fiber and the matrix. The fiber is modeled as transversely isotropic linear-elastic, and the matrix as isotropic elastic-plastic material. Using proposed model, the effects of the interface region and fiber arrangement in MMCs on the distributions of stress and strain are evaluated. The stress distributions of a thin multi layer interface have much less changes compared with conventional perfect interface. The analyses were based on a two-dimensional generalized plane strain model of a cross-section of an unidirectional composite by the ANSYS finite element analysis code.

• International Journal of Highway Engineering
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• v.18 no.5
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• pp.39-47
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• 2016

PURPOSES : Road subsidence occurs owing to road cavities, which cause many social and environmental problems, especially in cities. Recently, road cavities were detected by various ground radars and repair works were carried out against the detected cavities. The condition assessments related to the road cavities are necessary to understand the potential risk of the cavities. Therefore, in this study, a numerical study was performed to assess the various conditions of road cavities. METHODS : The numerical method adopted in this study is the discrete element approach, and it is suitable for analyzing the condition because it can consider the movement of the soil particles in the surrounded cavity areas. In addition, the triaxial test was modeled and performed under various cavity conditions inside the specimens. RESULTS : The conditions of different cavity locations and shapes were analyzed to identify the effect of cavity state. Three general cases of particle size distributions were formulated to identify the effect of surrounding ground conditions. As a result, the degree of decrement and volumetric strain were varied depending on the locations and shapes of the cavity. Only minor changes were observed when the particle size distributions were altered. CONCLUSIONS : The strength reduction was higher when the cavity formed was larger and located in the upper zone. Similar to the cavity shape, strength reduction and volume deformation are more influenced by the width than the length of the cavities. There is an influence from ground conditions such as the particle size distribution, especially on the wide cavity.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.151-151
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• 2011

Large amounts of natural gas, mainly methane, in the form of hydrates are stored on continental margins. When gas hydrates are dissociated by any environmental trigger, generation of excess pore pressure due to released free gas may cause sediment deformation and weakening. Hence, damage on offshore structures or submarine landslide can occur by gas hydrate dissociation. Therefore, geotechnical stability of gas hydrate bearing sediments is in need to be securely assessed. However, geotechnical characteristics of gas hydrates bearing sediments including small-strain elastic moduli have been poorly identified. Synthesizing gas hydrate in natural seabed sediment specimen, which is mainly composed of silty-to-clayey soils, has been hardly attempted due to their low permeability. Moreover, it has been known that hydrate loci in pore spaces and heterogeneity of hydrate growth in specimen scale play a critical role in determining physical properties of hydrate bearing sediments. In the presented study, we synthesized gas hydrate containing sediments in an instrumented oedometric cell. Geotechnical and geophysical properties of gas hydrate bearing sediments including compressibility, small-strain elastic moduli, elastic wave, and electrical resistivity are determined by wave-based techniques during loading and unloading processes. Significant changes in volume change, elastic wave, and electrical resistivity have been observed during formation and dissociation of gas hydrate. Experimental results and analyses reveal that geotechnical properties of gas hydrates bearing sediments are highly governed by hydrate saturation, effective stress, void ratio, and soil types as well as morphological feature of hydrate formation in sediments.

• Journal of the Korea Concrete Institute
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• v.27 no.1
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• pp.45-53
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• 2015

In general, RC columns are reinforced by spiral or tied steel and a strength of confined concrete is more increased than this of unconfined concrete. And strength and ductility of column are increased by a confinement effect. A confinement effect is affected by concrete strength, spacing, volume and strength of confinement steel. Many researchers suggested various confinement models which reflected these parameters by many experimental results. In this study, a load-strain relationship is evaluated by a confinement model in EC2, and it is compared with Mander model, Saatchioglu-Razvi model and Cusson et al. model. As results, it is appeared that a confinement model in EC2 is able to apply all kinds of concrete strength and a consistency in sectional analysis can be secured using material models in EC2. In parameter studies using material models in EC2, a confinement effect is more affected by a confinement steel than a concrete strength.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Journal of Life Science
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• v.18 no.6
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• pp.871-877
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• 2008

Onions are considered to be a promising source of the alcoholic drink because they are rich in sugar, amino acids and various nutrients. To isolate strains of Saccharomyces cerevisiae producing ethanol of higher concentration, 19 strains were subjected to screening. Among them, the strain producing the highest concentration of ethanol was OJ-8 strain. Onion's oder was effectively removed by treatment for 30 min with 10% (w/v) charcoal against medium and then heat treatment of onion extract for 40 min at $100^{\circ}C$. The optimum conditions for alcoholic fermentation was investigated in medium containing the onion extract. The optimal conditions for ethanol production was obtained by standing culture for 5 days at $25^{\circ}C$ with 5% inoculum volume.

• Textile Coloration and Finishing
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• v.24 no.1
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• pp.69-78
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• 2012

This paper surveys the physical properties of the MWNT dispersion solution dispersed with the three types of solvents and of the polyurethane composite film for improvement of mechanical properties and electrical characteristics of PU/MWNT composite film. For this purpose, the MWNT dispersed solution was mixed with three types of solvent such as IPA, MEK and Toluene and then mixed with polyurethane (100part) with variation of loading content (0, 10, 20, 30, 40, 50 part) of MWNT dispersed solution in the ultrasonic wave dispersion apparatus. And eighteen PU/MWNT composite films were prepared as specimens. The various physical properties of these PU/MWNT films were measured and discussed with the loading content of three types of MWNT dispersed solutions. The highest absorbancy among the three types of dispersed solutions was shown in the IPA/MWNT solution. But the absorbancy of PU/MWNT films was not same as the solution. The low electrical surface and volume resistivity of PU/MWNT film were shown at the condition of 20 and 10 parts loading of IPA/MWNT dispersed solution, respectively. The low triboelectricity of PU/MWNT film was shown at the condition of above 30part loading of IPA/MWNT dispersed solution. The breaking strength and strain of PU/MWNT film prepared with IPA/MWNT dispersed solution were decreased with increasing loading content of IPA/MWNT from 10 to 40 parts. The maximum breaking strength and breaking strain according to the dispersion solution were shown on the IPA/MWNT dispersed solution. The uniform dispersion of PU/MWNT film according to the loading content of MWNT solution was shown by surface image analysis on the films dispersed with IPA.

• Safety and Health at Work
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• v.9 no.2
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• pp.232-235
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• 2018

Background: This study was conducted to investigate the heat stress and semen quality among male workers in a steel industry in Iran and investigate the relationship between heat stress indices and semen parameters. Methods: The study was conducted on workers exposed (n = 30) and unexposed (n = 14) to heat in a steel industry. After obtaining a brief biography of the selected employees, scrotal temperature, oral temperature, and environmental parameters were measured, and their semen samples were analyzed according to the procedure recommended by the World Health Organization. The heat stress indices, including wet-bulb globe temperature (WBGT) and predicted heat strain (PHS), in their workplace were calculated according to environmental parameters (ISO 7243:1989 and 7933:2004, respectively). Results: Time-weighted averages of WBGT and PHS ($35.76^{\circ}C$ and 491.56 $w/m^2{\frac{w}{m^2}}$, respectively) for the exposed group were higher than threshold limit values. The mean difference of environmental, physiological, and semen parameters (exception: pH of semen), and also WBGT and PHS indices were statistically significant (p < 0.05) between the two groups. Mean semen parameters were in the normozoospermic range. WBGT and PHS indices showed significantly "negative" correlation with physiological parameters (scrotal and oral temperature) and most semen parameters (semen volume, sperm morphology, sperm motility, sperm count; p < 0.05); moreover, the correlation of WBGT with these parameters was stronger than PHS. Conclusion: Semen parameters of the studied workers exposed to heat were in the borderline level of normozoospermic range, and their semen parameters were significantly lower than controls. For better assessment of occupational environment concerning physiological and semen parameters in steel industries, WBGT can be a more useful index.

• Korean Journal of Materials Research
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• v.26 no.7
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• pp.370-375
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• 2016

Tensile tests and creep tests were carried out at high temperatures on an Al-$Al_4C_3$ alloy prepared by mechanical alloying technique. The material contains about 2.0% carbon and 0.9% oxygen in mass percent, and the volume fractions of $Al_4C_3$ and $Al_2O_3$ particles are estimated at 7.4 and 1.4%, respectively, from the chemical composition. Minimum creep rate decreased steeply near two critical stresses, ${\sigma}_{cl}$ (the lower critical stress) and ${\sigma}_{cu}$ (the upper critical stress), with decreasing applied stress at temperatures below 723 K. Instantaneous plastic strain was observed in creep tests above a critical stress, ${\sigma}_{ci}$, at each test temperature. ${\sigma}_{cu}$ and ${\sigma}_{ci}$ were fairly close to the 0.2% proof stress obtained by tensile tests at each test temperature. It is thought that ${\sigma}_{cl}$ and ${\sigma}_{cu}$ correspond to the microscopic yield stress and the macroscopic yield stress, respectively. The lower critical stress corresponds to the local yield stress needed for dislocations to move in the soft region within subgrains. The creep strain in the low stress range below 723 K arises mainly from the local deformation of the soft region. The upper critical stress is equivalent to the macroscopic yield stress necessary for dislocations within subgrains or in subboundaries; this stress can extensively move beyond subboundaries under a stress above the critical point to yield a macroscopic deformation. At higher temperatures above 773 K, the influence of the diffusional creep increases and the stress exponent of the creep rate decreases.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.233-240
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• 2012

Hybrid SHCC is being researched actively for its excellent performance in controlling macro and micro cracks using macro and micro fibers, respectively. However, a significant autogenous shrinkage of SHCC is expected since it possesses high unit cement volume in its mix proportion, resulting in autogenous shrinkage cracks. Therefore, this study was performed to evaluate mechanical property of shrinkage-reducing type hybrid SHCC mixed together with steel fiber and PE fiber with excellent micro/macro crack controlling performance. In order to evaluate mechanical property of shrinkage-reducing type hybrid SHCC, replacement ratios of 0% and 10% of expansive admixture and water to binder ratios of 0.45, 0.3, and 0.2 were considered as variables. Then, shrinkage, compressive, flexural, and direct tensile tests were performed. The test results showed that mix proportion with W/B 0.3 significantly improved mechanical performance by using 10% replacement of expansive admixture.