• Title/Summary/Keyword: shrinkage method

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Cavity Design for Injection Molded Gears by the Compensation Method of Design Parameters (설계인자 보정방법에 의한 사출성형기어의 캐비티 설계)

  • Lee, Sung-Chul;Kim, Choong-Hyun;Kwon, Oh-Kwan;Huh, Yong-Jeong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.10
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    • pp.3142-3151
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    • 1996
  • As plastics shrink when changing from a molten to a solid state, mold cavities must by made larger than the product specification, In making molded gears, the teeth in the cavity must be carefully compensated for shrinkage so that the teeth of gears will have the correct profile. Two compensation methods are widely used in the cavity design. One is the compensation of a module and the other is the modification of a pressure angle and profile shifting coefficient. These methods, however, do not provide a gear cavity with all disign parameters for gears and several parameters are determined by experience. In this paper, the new design technique, namely the compensation method of design parameters, was proposed , which is based on the three kinds of shrinkage rates obtained from the measuring data of the prototype of molded gears. Using the shrinkage rates in the tip circle, tooth heigth and tooth thickness, we calculate the whole design parameters of a gear cavity. Thus, the gear cavity is considered as a complete gear with the compensated module, pressure angle, profile shifting coefficient, clearance coefficient and back lash amount so that the formula of gears can be applied to the cavity design effectively. Experimental results show that more precision molded gears can be made by using the proposed design method.

Drying Shrinkage of Concretes according to Different Volume-Surface Ratios and Aggregate Types (형상비 및 골재의 종류에 따른 콘크리트 시편의 건조수축특성 연구)

  • Yang, Sung-Chul;Ahn, Nam-Shik;Choi, Dong-Uk;Kang, Seoung-Min
    • International Journal of Highway Engineering
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    • v.6 no.4 s.22
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    • pp.109-121
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    • 2004
  • This study was performed to investigate the characteristics of drying shrinkage for concrete slabs as a project for Korean pavement design procedure. According to the volume-surface ratios and aggregate types, the experiments have been executed for 252 days. In order to simulate the volume-surface ratio of a real concrete pavement slab, three-layer epoxy coating and wrapping were used to prevent the evaporation at the part of specimen surfaces. As a result of preliminary test, coating and wrapping method was identified as reliable for three months. According to the volume-surface ratio, the drying shrinkage of the concrete specimen using sandstone was measured 1.32 to 1.8 times higher than that of the limestone specimen. Comparing to the measured drying shrinkage strains and established ACI and CEB-FIP model equations, it turned out that those model equations were underestimated. Finally, considering the age and volume-surface ratios, the prediction equations of the drying shrinkage of concrete specimen were proposed through a multiple nonlinear regression analysis.

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Strength Development and Drying Shrinkage in Recycled Coal-Ash Building Material (석탄회를 재활용한 건설소재의 강도발현 및 건조수축)

  • Jo, Byung-Wan;Kim, Young-Jin;Park, Jong-Bin
    • Journal of the Korea Concrete Institute
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    • v.15 no.5
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    • pp.670-678
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    • 2003
  • Recently, since industrial waste and life waste leaped into a pollution source, the building material used now a days is striking the limit. The purpose of this paper is to investigate an application of recycled coal ash using non-sintering method in the construction field. Accordingly, compressive strength, elastic modulus and drying shrinkage were experimentally studied for hardened coal ash using the non-sintering method. Also, Lineweaver and Burk method were applied to the regression analysis of drying shrinkage for the proposal equation. Elastic modulus, compressive strength of material become the basis properties of structural design. And these properties by age for hardened coal ash are important because of change by pozzolan reaction. This hardened coal ash is weak for tensile stress like that of concrete. And drying shrinkage is very important factor to make huge tensile force in early age. In the results, although some differences were shown when comparing coal ash with mortar or concrete, the application as a building material turned out to be possible if further researches were carried out. And the shrinkage characteristic of hardened coal-ash reveals to be similar to that of moderate heat cement.

A STUDY ON THE EVALUATION OF POLYMERIZATION SHRINKAGE OF COMPOSITE AND COMPOMER USING STRAIN GAUGE METHOD (스트레인 게이지법을 이용한 복합레진과 컴포머의 중합수축 평가에 관한 연구)

  • Kim, Yeun-Chul;Kim, Jong-Soo;Kwon, Soon-Won;Kim, Yong-Kee
    • Journal of the korean academy of Pediatric Dentistry
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    • v.29 no.1
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    • pp.19-29
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    • 2002
  • The purpose of this study was to compare the polymerization shrinkage and the compressive strength of composite and compomer cured with two different light sources ; conventional halogen-light curing unit and recently-developed plasma arc curing unit. The 'strain gauge method' was used for determination of polymerization shrinkage and the compressive strength was measured by universal testing machine. The results of the present study can be summarized as follows: 1. Filling materials in polyethylene molds showed the initial expansion in the early phase of polymerization. This was followed by the rapid contraction in volume during the first 60 seconds and gradually diminished as curing process continued. 2. The polymerization shrinkage in tooth samples was generally lower than in the mold samples. 3. The generally lower amount of linear polymerization shrinkage was observed in compomer and plasma arc curing unit group when compared to composite and conventional curing unit. 4. The higher compressive strength values was found in composite groups regardless curing methods. The results of this study strongly support the application of plasma arc system and fluoride-containing compomer in the field of clinical pediatric dentistry claiming its effectiveness in curing the esthetic dental materials and the anticariogenic capacity.

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POLYMERIZATION SHRINKAGE OF COMPOSITE RESINS CURED BY VARIABLE LIGHT INTENSITIES (가변 광도 중합에 따른 복합레진의 중합수축에 관한 연구)

  • Lim, Mi-Young;Cho, Kyung-Mo;Hong, Chan-Ui
    • Restorative Dentistry and Endodontics
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    • v.32 no.1
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    • pp.28-36
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    • 2007
  • The purpose of this study was to compare the effect of exponential curing method with conventional curing and soft start curing method on polymerization shrinkage of composite resins. Three brands of composite resins (Synergy Duo Shade, Z250, Filtek Supreme) and three brands of light curing units (Spectrum 800, Elipar Highlight, Elipar Trilight) were used. 40 seconds curing time was given. The shrinkage was measured using linometer for 90 seconds. The effect of time on polymerization shrinkage was analysed by one-way ANOVA and the effect of curing modes and materials on polymerization shrinkage at the time of 90s were analysed by two-way ANOVA. The shrinkage ratios at the time of 20s to 90s were taken and analysed the same way. The results were as follows : 1. All the groups except Supreme shrank almost within 20s Supreme cured by soft start and exponential curing had no further shrinkage after 30s (p < 0.05). 2. Statistical analysis revealed that polymerization shrinkage varied among materials (p = 0.000) and curing modes (p = 0.003). There was no significant interaction between material and curing mode. 3. The groups cured by exponential curing showed the statistically lower polymerization shrinkage at 90s than the groups cured by conventional curing and soft start curing (p < 0.05). 4. The initial shrinkage ratios of soft start and exponential curing were statistically lower than conventional curing (p < 0.05). From this study, the use of low initial light intensities may reduce the polymerization rate and, as a result, reduce the stress of polymerization shrinkage.

Cracking Behavior of Concrete Box Culvert for Power Transmission Due to Drying Shrinkage (전력구 콘크리트 구조물의 건조수축 균열특성에 관한 연구)

  • Woo, Sang-Kyun;Chu, In-Yeop;Kim, Ki-Jung;Lee, Yun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.1
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    • pp.1-8
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    • 2016
  • The purpose of this study is to predict the cracking behavior and suggest the method of controlling the cracking in concrete box culvert for power transmission due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis cor responding to drying shrinkage on concrete box culvert are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of box culvert shows the different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

Polymerization Shrinkage Behavior Measured by Digital Image Correlation for Methacrylate-based and Silorane-based Composites During Dental Restoration (디지털 이미지 상관법을 이용한 Methacrylate기질과 Silorane기질 복합레진의 치아 수복 시 중합수축거동)

  • Park, Jung-Hoon;Choi, Nak-Sam
    • Composites Research
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    • v.33 no.3
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    • pp.125-132
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    • 2020
  • The polymerization shrinkage behavior of dimethacrylate-based composite (Clearfil AP-X, Kuraray) and silorane-based composite (Filtek P90, 3M ESPE) used for dental composite restorations was measured using digital image correlation method. The stress distribution on the surface of specimen was calculated by finite element analysis with equivalent elastic modulus and was compared with the measured shrinkage distribution. Camera images were monitored by a CCD camera during and after the irradiation of light. As a result of the DIC analysis, a non-uniform shrinkage distribution was observed in both composite resins, and the resin core inside the ring specimen had free flowability, leading to in greater shrinkage strain than the resin/ring interfacial region. It was observed that as the distance from the center of the resin increased, the radial average shrinkage strain decreased. The radial average shrinkage strain during light irradiation occurred to be 33% for P90 and 57% for AP-X of the entire strain at the end of the test. The shrinkage behavior of P90 and AP-X was measured to be significantly different from each other during light irradiation. In the resin near the resin/ring interface, it was confirmed that the tensile strain rapidly formed to increase after light irradiation, causing a tensile stressed, interface weak.

Cracking Behavior of Concrete Bridge Deck Due to Differential Drying Shrinkage (교량 바닥판 콘크리트의 부등건조수축 균열특성에 관한 연구)

  • Yang, Joo Kyoung;Lee, Yun;Yang, Eun Ik;Park, Hae Geun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.4A
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    • pp.329-335
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    • 2009
  • The purpose of this study is to provide the efficient method and guideline of controlling the cracking in bridge deck concrete due to differential drying shrinkage. Drying shrinkage cracking is mainly influenced by the moisture diffusion coefficient that determines moisture diffusion rate inside concrete structures. In addition to the diffusion coefficient, surface coefficient of concrete surface and relative humidity of ambient air simultaneously affect the moisture evaporation from concrete inside to external air outside. Within the framework of cracking shrinkage cracking mechanism, it is necessary to conceive the numerical analysis, which involves these three influencing factors to predict and control the shrinkage cracking of concrete. In this study, moisture diffusion and stress analysis corresponding to drying shrinkage on bridge deck are performed with consideration of diffusion coefficient, surface coefficient, and relative humidity of ambient air. From the numerical results, it is found that cracking behavior due to differential drying shrinkage of bridge deck concrete shows different feature according to three influencing factors and the methodology of controlling of drying shrinkage cracks can be suggested from this study.

A Study on Construction Method for Joints between Old and New Concrete Deck Slabs (콘크리트 교량 바닥판 신구접합부의 시공방안에 관한 연구)

  • Paek Nak Seung;Choi Young Chul;Cha Soo Won;Oh Byung Hwan
    • 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.

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