• Proceedings of the KAIS Fall Conference
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• 2008.11a
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• pp.371-374
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• 2008

본 연구에서는 무도장 Weldless 평가금형을 이용하여 사출성형 공정조건에 따라 다양한 형태의 변형이 생기는 성형품을 CAE를 통하여 ABS와 PC의 사출조건 냉각시간, 보압의 유/무 등에 따라서 발생되는 문제점과 변형량을 예측하고, 실제 사출성형 되어진 성형품과의 비교 분석을 통하여 사출성형 CAE 해석을 실제 사출성형 공정에서의 활용방안에 대하여 검토하였다.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.7-12
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• 1998

The waste sludge is by-produced about 20-30% of total production and arised to the severe problems of this mine's surrounding environmnet. This study was invested the composition of component, particle of size of the waste sludge by Chemical Analysis, X, R, D, Particle Size Analyzer and the physical properties (air content, slump, strength, etc) of concrete when the waste sludge is added into concrete. so, It's recomended the proper content of the waste sludge to be added into concrete. and then, is verified to be applied at batch plant in field. Above the results, the recomeded content of the waste sludge is about 2-4% (about 4-8% in cement) in aggregates and when it's added the recomended content, they are detected to be more or less changed the physical properties of concrete, ( equally strength and durability, little less air con tent, little increased shinkage, etc). but the application of the recomended content don't arise the problem of the basic quality control of concrete and physical properties.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.363-366
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• 2005

When widening or repairing concrete deck slab, there is a joint inevitably. However, joining-construction method have following problem, that is the additional stress in existing part of bridge resulting from the specific process of joining-construction and the difference of amount of shrinkage between new and existing bridge. On this study, compared shrinkage stress of the direct joining construction method with the indirect joining construction method, and concluded the proper substitution rate of expansion cement. The rate of replacement was proper at $10\%$. but more than $15\%$, concrete had excessive expansion and weeker compressive strength. The time of placing closure concrete, considering the shinkage stresses and creep, was suitable in $45\~60$ days after placing the new concrete deck slab.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.84-88
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• 1995

The results of an experimental study on manufacture and mechanical properties of concrete utilizing crushed sand and fly ash for construction materials are presented in theis paper. As the results show, the workability, compressive strength and freezing-thaw resistance were improved by proper contents of fly ash, replaced crushed sand, and air entraining agent. And the drying shinkage was decreased by proper contents of those. Also, the suitable weight contents of replacing ratio of crushed sand and weight ratio fly ash in concrete using crushed sand were in range of 30% and 15% respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.04a
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• pp.7-11
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• 1996

The results of an experimental study on the mechanical properties of concrete utilizing crushed sand for construction materials are persented in this paper. As the results show, the workability, compressive strength and drying shrinkage were improved by propeer contents of replaced crushed sand. And the workability, compressive strength and drying shinkage were decreased by increasing very fine sand. Also, the suitable weight contents of replacing ratio of crushed sand in concrete using crushed sand were in range of about 30%. And the use of crushed sand containing very fine sand under the permitted limit by regulated KS F 2558 has not very much problems in concrete.

• Design & Manufacturing
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• v.2 no.4
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• pp.54-61
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• 2008

Warpage, which is one of the molding trouble, acts as possible factor which results in defect in assembly. In this study, a mold was designed to produce specimens with rib parallel to flow direction, specimens with rib perpendicular to flow direction and specimens without rib. This work researched change of warpage according to injection molding condition such as injection pressure, packing pressure, packing time, resin temperature, mold temperature in non-crystalline resins(PC, ABS), crystalline resins(PP, PA66), and 30% glass fiber reinforced-resins(PC, ABS, PP, PA66).Specimens with rib and Crystalline resins show more warpage than specimens without rib and non-crystalline resins, respectively. Glass fiber reinforced-resins and specimens with rib parallel to flow direction show smaller warpage than conventional resins and specimens with rib perpendicular to flow, respectively. Specimens with rib and specimens without rib show reduced warpage as packing time increases. In addition, warpage increase as resin temperature increases. It is found that CAE shows similar tendency with experiment as packing time, resin temperature. when the rib is caused, warpage will reduce and prevent the transformation. product of a irregular form occurs warpage. In the study It'll be basic data that product occurs warpage, preferablity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.6
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• pp.884-895
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• 1997

The finite element analysis for the tubular alumina liner which was shrink-fitted into a heat treated high speed steel (HSS) sleeve and subjected to high inner pressure and high temperature was performed. The parameters for the analysis were the interference between the alumina and the HSS, the temperature, the inner pressure, the coefficient of friction between the alumina and the HSS, and the taper at the sleeve ends. From the analysis, it was found that the tensile hoop stresses were decreased when the end parts of the HSS sleeve were tapered and the tensile stresses were decreased as the coefficient of friction between the alumina and the HSS was decreased. Also it was found that the alumina might be used as the structural liner for high pressure and high temperature when it was shrink-fitted into a heat treated HSS sleeve.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.152-157
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• 2014

The objective of this study is to examine the drying shinkage and autogenuous shrinkage strains of heavyweight magnetite concrete. As a main parameters, cement was partially replaced by fly ash (FA) from 5% to 35%. The measured shrinkage strains were compared with predictions obtained from CEB-FIP equations and Yang et al.'s model. Test results showed that the magnitite of the autogenous and total shrinkage strains of heavyweight concrete slightly increased as the amount of fly ash increases up to 15%, beyond which the strains tended to decrease. The CEB-FIP equations considerably underestimated the shrinkage behavior of heavyweight concrete, indicating that this trend was more notable with the age. On the other hand, Yang et al.'s model predicted accurately the shrinkage of heavyweight concrete.

• Journal of the korean academy of Pediatric Dentistry
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• v.25 no.2
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• pp.368-382
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• 1998

The purpose of this study is to evaluate and compare the results of argon laser for 5 seconds, argon laser for 10 seconds, and visible light for 40 seconds photo-polymerization in compressive strength, microhardness, curing depth, temperature rising during polymerization, and polymerization shrinkage. Hybrid type composite resin(Z-100) and compomer(Dyract) were used to be compared. The compressive strength was measured by an Instron(1mm/min cross head speed) in 60 specimens and the microhardness of the surface was expressed by Vickers Hardness Number(VHN) in 30 specimens. The curing depth was evaluated comparing the different values of upper and lower VHN according to irradiation time and thickness for the light source polymerization in 60 specimens. The temperature rising during photopolymerization was observed by the temperature change with thermocouple sensitizer beneath 40 specimens at the argon laser for 10 seconds and visible light 40 seconds irradiation. The polymerization shinkage was evaluated by calculating the decrease of % volume by using a dilatometer in 30 specimens. The results were as follows ; 1. In the case of compressive strength, the argon laser polymerization groups were higher than visible light group in Z-100 (p<0.05). In Dyract, the argon laser 5 seconds group did not show a significant difference with the visible light 40 seconds group. The argon laser 10 seconds group showed the markedly low value when compared with other groups (p<0.05) 2. In microhardness, Z-100 was better than Dyract when comparing by VHNs (p<0.05); however, there was not a significant difference between two materials in the visible light 40 seconds group and the argon laser 10 seconds group. 3. In the study of curing depth, Z-100 showed the consistent polymerization in argon laser irradiation because there was no difference in the VHN decrease according to the thickness change. Over the thickness control, the results did not show a significant difference between visible light and argon laser group in Z-100; however, in the case of Dyract, the visible light 40 seconds group was better than the argon laser groups(p<0.05). 4. There was a significant difference between the two materials in temperature rising during polymerization (p<0.05), but not a significant difference between irradiation times, 5. There was not a significant difference between the two materials in polymerization shrink age. The argon laser 5 seconds group was smaller than the other groups (p<0.05). It could be concluded that Z-100 polymerization was recommended to use the argon laser for reduction of the irradiation time while Dyract was recommended to use the visible light polymerization.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.295-301
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• 2011

Recently, the use of UHPC made of superplasticizers, silica fume, and steel fibers has been increasing worldwide. Although UHPC has a very high strength as well as an excellent durability performance due to its dense microstructures, earlyage cracks may occur due to the high heat of hydration and autogenous shrinkage caused by low W/B and high unit cement content. The early-age shrinkage cracking of UHPC can be controlled by using the shrinkage reducers and expansive admixtures having autogenous shrinkage compensation effect. In this paper, ultrasonic pulse velocity of UHPC containing shrinkage reducers and expansive agents was measured to predict its stiffness change. Also, the effect of shrinkage reducers and expansive agents on the autogenous shinkage of UHPC was investigated through the shrinkage test of UHPC specimens. Furthermore, the material coefficients of autogenous shrinkage prediction model were determined using the autogenous shrinkage values of UHPC with age. Consequently, the test results showed that, by adding shrinkage reducers and expansive agents, the stiffness of UHPC was rapidly developed at early-ages and the autogenous shrinkage was considerably reduced.