• Clean Technology
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• v.17 no.3
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• pp.191-200
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• 2011

Natural polymers, biopolymers, and synthetic polymers based on renewable resources are the basis for the 21th portfolio of sustainable and eco-friendly plastics but high-volume consumable plastics continue to be dominated by nondegradable petroleum-based materials. Three factors have recently made biodegradable polymers economically attractive: (i) rising costs of petroleum production resulting from the depletion of the most easily accessible reserves, (ii) environmental and economic concerns associated with waste plastics, and (iii) emissions of carbon dioxide from preparation of petroleum-based materials. These pressures have driven commercial applications based on biodegradable polymers which are related to reduction of carbon dioxide in processing, such poly(hydroxy alkanoate) and poly (lactide). Since initial degradation of these polymers leads to catastrophic mechanical failure, it is necessary to control the rate of initial degradation for commercial applications. In this article, we have a critic review on the recent progress of polymer modification for the control of degradation.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.4
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• pp.213-220
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• 2020

In the present paper, implosion responses of two adjacent cylindrical tubes under external hydrostatic pressure were experimentally investigated. The cylinder models were fabricated of aluminium alloy 6061-T6 commercial tubes. In the experiment, a pair of two-cylinders were placed inside of a support frame in a medium-size pressure chamber, whose design pressure was 6.0MPa. The distance between the two-cylinders was 30 millimeter measured from outer shell at the mid-length. The implosion tests were performed with water and compressed nitrogen gas as the pressurizing media. The ambient static pressure of the chamber and local dynamic pressure near the two-imploded models were measured simultaneously. It was found that the energy released during an implosion from the first, weaker cylinder triggered the instability of the second, stronger cylinders. In other words, the resulting shock wave of the first implosive impact from the weaker cylinder could cause the premature failure of the neighboring stronger cylinders. The non-contact implosion phenomena from the two-cylindrical tube were clearly observed.

• Journal of the Korean Wood Science and Technology
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• v.24 no.1
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• pp.81-86
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• 1996

This study was performed to evaluate the reduction in bending properties of radiata pine sapwood associated with incipient brown-rot decay. Decayed bending specimens by Tyromyces palustris and Gloeophyllum trabeum for varoious periods were tested destructively. Brown-rot decay by T. palustris and G. trabeum caused serious reduction in bending properties at very early stages of decay, with about 30 percent decrease in bending strength observed for only 1~2 percent weight loss. In general, the reduction in bending properties caused by T. palustris was somewhat greater than that by G. trabeum. Work to maximum load was reduced most severely and rapidly from the onset of decay, while modulus of elasticity showed a much more moderate rate of reduction. Modulus of rupture was affected by decay to a greater extent than was modulus of elasticity. Since a relatively strong correlation between weight loss and bending strength was observed, the residual strength of decayed wood can be predicted by weight loss due to decay. The results of this study indicate that very early stages of brown-rot decay reduce the bending strength significantly. Thus, it is recommended that all load-bearing members in wooden structures, especially those that are periodically wetted, should be inspected regularly to prevent a sudden failure even though there are no definite signs of decay.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.1
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• pp.85-94
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• 2016

In this study, a non-linear FEM model is presented to predict the static flexural performance of precast bridge decks with ribbed joint and is verified with previous experiment results through comparison. The several theory of material properties were applied to each mechanical properties in FEM model and FEM model's input variables were determined through experiment result and parametric study. The FEM results showed good accuracy in predicting the structural performance of the specimens and FEM model's average error rate was 5%. Also, each specimen's cracking aspect and failure mode can be predicted through FEM's plastic strain distribution. Thus, this FEM model can be used effectively for predicting the ultimate behavior and parametric study to development of design formula for joint.

• Journal of Powder Materials
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• v.5 no.1
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• pp.42-49
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• 1998

A study on the improvement of the impact energy in 93W heavy alloy with a Ni/Fe ratio of 9/1 has been carried out as a function of heat treatment temperature. The obtained results were compared to that of the traditional alloy system in which the Ni/Fe ratio is 7/3 or 8/2. With increasing heat treatment temperature from 1150 to 125$0^{\circ}C$, the impact energy of the alloy with the Ni/Fe ratio of 9/1 is remarkably increased from 42 to 72 J, which is higher than that of traditional alloy, up to 118$0^{\circ}C$ and then saturated. Fracture mode was also changed from brittle W/W boundary failure to W cleavage. The temperature showing the dramatic shrinkage by dilatometric anaysis of the heavy alloy with Ni/Fe ratio of 9/1 was found to be 1483 $^{\circ}C$, which is higher than that (146$0^{\circ}C$) of the heavy alloy with Ni/Fe ratio of 7/3. Auger Electron Spectroscopy showed that the segregation of impurities, such as S, P, and C in W/W grain boundary was considerably decreased with increasing heat treatment temperature from 1150 to l18$0^{\circ}C$. From the above results, it was found that the impurity segregation in W/W grain boundary played an important role on the decrease of impact properties, and the heat treatment temperature should be appropriately chosen, as considering the Ni/Fe ratio of the alloy, in order to get good impact properties.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.500-509
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• 2000

In general, the three major oral functions of edentulous patients-mastication, phonation, esthetics-can be rehabilitated by the complete dentures, and both the resin based complete denture and the metal based complete denture are commonly used by many clinicians today. For the sake of many advantages such as the excellent thermal conductivity, low volumetric change, high strength, low risk of fracture and the better patient's adaptation, the metal based complete dentures are indicated to the several cases. But, there are common failures of these type of dentures mainly by the fracture or the debonding between the resin structures and the metal frameworks which is caused by the discrepancies of the flexural strength and the coefficient of thermal expansion. This is aggravated by the water contamination of the interface when exposed to the oral environment and results in the failure of complete denture treatment. So, the purpose of this study is to compare the bond strength and the fracture patterns of the gold alloy based and the Co-Cr alloy based complete dentures using the PMMA resins and the 4-META adhesive resins. The results of this study were as follows. 1. Both to the PMMA resin and the 4-META resin, the flexural bond strength of gold alloy is lower than that of Co-Cr alloy(P<0.05) 2. To the Co-Cr alloy, the bond strength of the 4-META resin is significantly higher than that of PMMA resin(P<0.05). 3. The flexural strength of the group with the mechanical retention form is significantly higher than that of the group without retention form(P<0.05). 4. Comparing with the other groups, the fracture patterns of the group 3 are quite different from the group 1,2,5.

• Journal of the Korean Ceramic Society
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• v.55 no.5
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• pp.492-497
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• 2018

This paper reports the efficacy of tape casting using an Ag-10 wt% CuO filler for the successful joining of a sintered $Ce_{0.9}Gd_{0.1}O_{2-{\delta}}-La_{0.7}Sr_{0.3}MnO_{3{\pm}{\delta}}$ (GDC-LSM) ceramic with a SUS 460 FC metal alloy by reactive air brazing. The as-prepared green tape was highly flexible without drying cracks, and the handling was easy when used as a filler material for reactive air brazing. Heat treatment for the GDC-LSM/SUS 460 FC joint was performed at $1050^{\circ}C$ for 30 min in air. Microstructural observations indicated a reliable and compact joining. The room temperature mechanical shear strength of the as-brazed joints was $60{\pm}8MPa$ with a cohesive failure. The flexural strength of joints was measured from room temperature up to $850^{\circ}C$, where the strength retention revealed to be almost 100% at $500^{\circ}C$. However, the joints showed a degradation in strengths at 800 and $850^{\circ}C$, exhibiting strength retentions of 57% and 37%, respectively.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.65-75
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• 2004

In this paper, a mechanism of the soil structure reinforced by geosynthetics is discussed. The reinforcing mechanism is interpreted as an effect arising from the reinforcement works preventing the dilative deformation (negative dilatancy) of soil under shearing. A full-scale in-situ model test was carried out in Kanazawa of Japan (1994), and in the laboratory test the strength and the characteristics of deformation conducting a constant volume shear test are examined. The parameters needed in the FEM are also applied by using the experimental data. The elasto-plastic finite element simulation is carried out, and the results are quantitatively compared with that of experiment. As a results, it is known that the theoretical predictions could explain effectively the experimental results which are obtained by a full-scale in-situ model test.

• Journal of the Korean Geotechnical Society
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• v.15 no.2
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• pp.181-194
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• 1999

Both the chemical components and the physical and mechanical properties of the compacted and undisturbed weathered granite soils were estimated to investigate the influences of the degree of weathering and saturation on the shear strength. The weathered granite soils used in this study were taken from six different sites in Korea. The results showed that the shear strength of weathered granite soil decreased with increasing the degree of weathering and saturation. Under the normal stresses less that 40kPa, the shape of Mohr-Coulomb failure envelope followed curved or hyperbolic relationship and a half of cohesion value obtained by the common shear test was observed. Using the Sueoka's method, the values of CWI were ranged from 21.5 to 31.26 which can be characterized as a completely weathered granite soil. Large decrease in shear strength and remarkable variation in dilatancy were observed in saturated granite soil compared to unsaturated soil. It was also found that the shear strength of undisturbed weathered granite soil of Pungam site can be expressed approximately by the equation of ${(\tau)_{sat}= 1.0(\tau)_{unsat}-12.48}$ and this equation can be extended to the other sites considered in this study.

• Journal of the Korean Institute of Gas
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• v.18 no.4
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• pp.68-75
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• 2014

It is necessary to control and evaluate human factors to reduce economic loss by major accident in toxic gas facilities. Conventional works to evaluate hazards have been focused on mechanical and systematic failure, while only a little works have been studied on managing human errors. In this work, a classification system of performance shaping factor (PSF) was suggested to consist human error in managing accident in the toxic gas facilities. Four types of PSFs (human, system, task characteristics, and task environment) were collected, reviewed, and analyzed to be categorized selected according their characteristics of situational, task, and environmental parameters. The PSFs were further modified to set up PSF systems adequate to evaluate human error, and the proposed system to consist PSFs to evaluate human error was further studied through accident analysis in toxic gas facilities.