• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.8
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• pp.807-812
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• 2009

Most structure engineers give the casting components over-estimated factor of safety without any reasonable foundation due to the worries about the unavoidable defects such as shrinkages and porosity in castings; the engineers have little knowledge on the relation between the defect and structural behavior. And the workers in casting field also do not know how to control the defects by manufacturing; they do not know to where the defects move or until how size they reduce the defects. In this study, shrinkage defect was scanned by industrial computerized tomography instrument (CT), and subsequently was modeled to a spheroid primitive for structural analysis. Using these simplified models of shrinkage, we observed the effects of the defect on the results of the structural analysis. A commercial structural analysis code was used to do the analysis works. Considering the conclusions, it is possible to manage the shrinkages effectively in casting process and to design the products with more reliable

• Journal of the Korean Ceramic Society
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• v.31 no.3
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• pp.321-329
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• 1994

Functionally gradient materials(FGM), which have the continuous or stepwise variation in a composition and microstructure, are being noticed as the material that solves problems caused by heterogeneous interface of coating or joining. And these materials also expect new functions occured by gradient composition itself. Therefore, to examine possibility of thermal barrier materials, TZP/Mo·FGM and TZP/Ni·FGM were fabricated by sintering method. As to the sintered specimens, sintering shrinkage, relative density and Vicker's hardness in each composition were examined. The phenomena due to the difference of sintering shrinkage velocity during sintering process and the thermal stress induced through differences of thermal expansion coefficient in FGM were discussed. And the structure changes at interface and microsturcture of FGM were investigated. As a results, the difference of shrinkage between ceramic and metal was about 14% in TZP/Mo and 7% in TZP/Ni. The relative density and hardness were considerably influenced by metal content changes. Owing to unbalance of sintering shrinkage velocity between ceramic and metal, various sintering defects were occured. To control these sintering defects and thermal stress, gradient composition of FGM should be narrow. The microstructure changes of FGM depended on the ceramic or metal volume percents and were analogous to the theoretical design.

• Journal of the Korean Wood Science and Technology
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• v.22 no.2
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• pp.61-70
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• 1994

This study was executed to find the applicability of press drying of tree disk by investigating the shrinkage and drying defect and to form appropriate model by comparing the actual moisture content(MC) and internal temperature in respect of drying time with calculated values based computer simulation to which was applied finite difference method. In press drying disk, heating period, constant drying rate period maintained plateau temperature at 100$^{\circ}C$ and falling drying rate period were significantly distinguished. Actual MC and internal temperature were analogous to those calculated at comparing points. Heat transfer model formed by Fourier's law using specific heat of moist wood and conduction coefficient considering fractional volume of each element of wood cell wall, bound water, free water and air showed applicability as basic data to developing heat expansion, shrinkage and drying stress during press drying. Also mass transfer model formed by Fick's diffusion law using water vapor diffusion coefficient showed applicability. Longitudinal shrinkage was developed by pressure of hot press and tangential shrinkage was restrained by hygrothermal recovery. The heart check, surface check and ring failure were occurred differently in species, but V-shaped crack didn't develop.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.215-218
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• 2005

This paper intended to evaluate the applicability of drying shrinkage reducing superplasticizer (DSRA) by investigating physical properties of concrete using DSRA, The application of flowing concrete method exhibited a less loss of slump and air content with time than those of conventional concrete and had small bleeding. Flowing concrete had larger compressive strength than base and conventional concrete by as much as $3\~5\%$. It also had less drying shrinkage by as much as $20\%$ compared with conventional concrete. This is due to the coupled effect of reduced water content and aqueous type expansive admixture. On the other hand, neutralization depth of flowing concrete showed greater than conventional concrete.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.681-687
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• 2002

The cumulative, shrinkage plastic strains and their distributions in the weld joint after completion of the welding process determine welding-induced distortion. Although the weldment undergoes many complex physical and metallurgical changes during welding, only the material plastic temperature range and its cooling history below this temperature range influence the [mal state of the cumulative shrinkage plastic strains. In addition, for structural welds, these plastic strains are uniform, except in the arc start and stop regions, along the weld. Therefore, the plastic strain-based "inherent shrinkage model" is effective and accurate to describe welding-induced distortion. This paper presents the theoretical background and numerical verification of this root cause.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.789-792
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• 2005

Development of high-strength concrete and improved durability has brought new opportunities to the construction industry. However, some attention was given to characteristics of such concrete, in particular with respect to their cracking sensitivity. It has been argued and demonstrated experimentally that a low water/cement ratio concrete undergoes shrinkage due to self-desiccation. This so-called autogenous shrinkage cracking is a major concern for concrete durability. One possible method to reduce cracking due to autogenous shrinkage is the addition of expansive additive. Tests conducted by many researches have shown the beneficial effects of addition of expansive for reducing the risk of shrinkage-introduced cracking. This paper aimed at forecasting deformation of high strength cement paste with expansive additive for early age.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.27-30
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• 2003

This study is investigated the various properties and drying shrinkage of concrete according to water content under the condition proper fluidity is adjusted, in order to suggest the method for reduction of crack by drying shrinkage. According to the results, though water content varies, slump and air content are satisfied to the planed values, but shear slump and separation happen at water content of 120 and 140kg/$m^3$ due to the overuse of superplasticizer(SP). As water content is diminished, setting time is retarded by an increase of the using amount of SP, and compressive and tensile strength increase in the range of 160-180kg/㎥ of water content, but decrease significantly at 120 and 140kg/$m^3$. Length change by drying shrinkage decrease with a decrease of water content. Therefore, considering not only drying shrinkage but also fluidity, setting time and strength, it proves that the most appropriate water content of concrete is 160kg/$m^3$ in the condition of this experiment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.6 no.4
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• pp.65-70
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• 2007

In this study, we analyzed about that after design form manufacture master pattern in Rapid Prototyping-RP through design program, processes to manufacture prototype using Vacuum Casting. In Rapid Prototyping-RP, there is an en-or by shrinkage of resin and, in Vacuum Casting, there is an error by shrinkage of silicon. To select condition which shrinkage become the minimum of each process, manufactured prototype after using Full Factorial Design of Design of Experiments, We could confirm shrinkage using reverse engineering and that result came into effect ANOVA 2-way. We applied errors of each process to master pattern, and then presented the method to improve flood control precision of prototype of Vacuum Casting.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.457-462
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• 2003

It studies the non-structural crack factors that are produced in Steel Box Girder Bridge concrete floor plate using analytical method. It mainly studies humidity and design standard of concrete strength. It used MIDAS CIVIL Ver 5.4.0, a general structure analysis program that applies drying shrinkage rate of domestic road bridge design standard and standard value of creep coefficient, CEF-FIP standard equation and ACI standard equation from the aspect of creep, drying shrinkage and hydration heat to see the effect of the two factors on concrete crack and found the following result. The analytical results of this study showed that the initial stress, which was obtained by ACI standard, exceeds the allowable tensile stress between 5 to 18 days. This result means that even if a bridge is designed and constructed according to design standard, the bridge can have cracks due to various variables such as drying shrinkage, hydration heat and creep that produce stress in slab.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1218-1219
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• 2006

The shrinkage variation of Low Temperature Cofired Ceramics(LTCC) limits the size of the substrates that impose limitations on embedded passive components. This paper focuses on the method of minimizing or controlling planar shrinkage and reducing distortion during firing. The laminated sheets of alumina and glass were sintered at varying temperature, and depending on the amount of the glass ceramics. When the sintered of multi-layer structure with $Al_2O_3/Glass/Al_2O_3$, the glass infiltrated entirely into $Al_2O_3$ layer at the temperature of about $950^{\circ}C$ or higher.