• The Korean Journal of Ceramics
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• 제1권1호
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• pp.45-54
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• 1995

Four kinds of silicon nitride based ceramic materials have been hot pressed. Effect of the sintering additives on the phase transformation, microstructural development and mechanical properties was investigated. While sintering under the same condition a big difference among the microstructures of the specimens, they appeared alike if sintered to have a similiar $\alpha$-$\beta$ phase ratio. The specimen of the stoichiometric $\alpha$-$\beta$ sialon composition showed very limited amount of the intergranular glassy phase and a significant degree of the residual stress. It exhibited almost no strength degradation up to $1300^{\circ}C$, and the strength of the specimen degraded more as its composition deviated from the stoichiometry.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.705-710
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• 2002

Welding is used not only during the shipbuilding, but also during the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, The result within identical materials showed that the heat-affected zone was slower than that of parent metal

• 한국정밀공학회지
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• 제19권11호
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• pp.75-82
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• 2002

Welding is used not only for the shipbuilding, but also for the repairing of ships. While repairing of ships, it is inevitable to weld new materials with degraded materials. In this case, it is predicted that the strength of both the sections is not identical each other. In this study, the respective welded joints in terms of mechanical properties such as microstructure, mechanical strength and fatigue crack propagation, with the component obtained from the barge used for a long-term period, were analyzed. It was found that the material degradation had a significant effect on the welded joints. The fatigue crack propagation in welded sections showed a big difference. The rate of fatigue crack growth of degraded material for both heat affected zone and parent metal was faster than that of new material. By contrast, the result from identical materials showed that the rate of fatigue crack growth of the heat-affected zone was slower than that of parent metal.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.179-184
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• 2001

The objective of this study is to clarify the seismic capacity and the characteristics in the hysteretic behavior of RC structures with nonseismic detailing. To do this, an exterior beam-column subassemblage was selected from a 10-story RC building and 6 1/3-scale specimens were manufactured with 3 variables; ⑴ with and without slab, ⑵ upward and downward direction of anchorage for the bottom bar in beams, and ⑶ with and without hoop bars in the joint region. The test results have shown that ⑴ the existence of slab increased the strength in positive and negative moment, 25% and 62%, respectively; ⑵ the Korean practice of anchorage (downward and 25 $d_{b}$ anchorage length) caused the 8% reduction of strength and the early strength degradation when compared with the case of seismic details; and ⑶ the existence of hoop bars in the joint region does not show significant difference because the size of column is much larger than that of beam.m.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.49-52
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• 2005

The purpose of this study is to investigate the relation between color change and residual compressive strength in concrete exposed to high temperature. In order to study the color image analysis, the specimens have been tested with variables of concrete strengths (20Mpa, 40Mpa, 60Mpa) in transient heating conditions($800^{\circ}C$ heating and 4 hour preservation). The results show that the residual strength of specimens are coincident with the full development of the pink/red color and the method may be used to define the distance from a heated surface where strength degradation has occurred.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.482-485
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• 2006

The response of a reinforced concrete element under cyclic shear is characterized by the hysteretic loops of the shear stress-strain curves. These hysteretic loops can exhibit strength deterioration, stiffness degradation, and a pinched shape. Recent tests have shown that the orientation of steel grids in RC shear elements has a strong effect on the "pinching effect" in the post-yield hysteretic loops. When the steel grid was set at a 45 degree angle to the shear plane, there was no pinching effect and no strength deterioration. However, when the steel grid was set parallel to the shear plane, there was a severe pinching effect and severe strength deterioration with increasing shear strain magnitude. In this paper, two RC elements subjected to revered cyclic shear stresses are considered to study the effect of the steel grid orientation. The presence and absence of the pinching mechanism in the post-yield shear hysteretic loops is studied using the Rotating Angle Softened Truss Model (RA-STM) theory.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집
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• pp.414-419
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• 2002

The dielectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability. First of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical. The breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised and the electric field is concentrated. In the case of (idled specimens with treating silane, the breakdown strength become much higher Finally, from the analysis of weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1[%], the applied field value needed to be under 21.5 MV/cm.

• 한국해양공학회지
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• 제10권4호
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• pp.58-66
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• 1996

The purpose of this investigation is to estimate the strength with the variations of the notch shape and the adgesive condition at the fiber/matrix micro interface of E-glass/PP laminates. To promote the degradation of the adhesive condition at the fiber/matrix micro interface without matrix dissolution loss, low-, hot-wet and spiking tests were carried out. The absorpotion properties and the tensile properties were compared accrding to the fiber orientation and the content. The results show that, firstly, saturated moisture absorption was reached at 5cycles and their absorptions of RD-40, UD-42 and UD-50 are 0.68%, 0.63%, 0.60%, respectively. Secondly, all the specimens investigated were mostly degraded at 5cycle, whereas UD-50 having ellipse shaped notch the least decrement of strength.

• 한국해양공학회지
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• 제11권4호
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• pp.23-30
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• 1997

The purpose of this paper is to investigate the water environmental effect on the mechanical properties of carbon fiber/epoxy composites. Moisture concentration absorbed in CFRP under various water environment was calculated and degradation of mechanical properties for each wet composite laminates is investigated by performing the flexual and tensile test. The results show that moisture absorption is accelerated in higher temperature environment and under the same temperature sea water environment prompts more absorption than fresh water. As increasing the water temperature and moisture concentration tensile and flexual strength decreased as much as 25%-40% compared with dry condition.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 춘계학술대회 논문집 유기절연재료 전자세라믹 방전플라즈마 일렉트렛트 및 응용기술
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• pp.212-217
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• 2002

The dielectric breakdown of epoxy composites used for transformers was experimented and then its data were simulated by Weibull distribution probability. First of all, speaking of dielectric breakdown properties, the more hardener increased the stronger breakdown strength at low temperature because of cross-linked density by the virtue of ester radical. The breakdown strength of specimens with filler was lower than it of non-filler specimens because it is believed that the adding filler forms interface and charge is accumulated in it, therefore the molecular motility is raised and the electric field is concentrated. In the case of filled specimens with treating silane, the breakdown strength become much higher Finally, from the analysis of weibull distribution, it was confirmed that as the allowed breakdown probability was given by 0.1[%], the applied field value needed to be under 21.5 MV/cm.