• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.581-590
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• 2011

Since ultra-high performance cementitious composites (UHPCC) not only represents high early age shrinkage strain due to its low water-to-binder ratio (W/B) and high fineness admixture usage but also reduces the cross section of structure from the higher mechanical properties, it generally has more shrinkage cracks from the restraints of formwork and reinforcing bars. In this study, free and restrained shrinkage experiments were conducted to evaluate the suitability of incorporating both expansive admixture (EA) and shrinkage reducing agent (SRA). The test results indi-cated that approximately 40~44% of free shrinkage strain was decreased. Also, the results showed that 35% and 47% of residual tensile stresses were relieved by synergetic effect of SRA and EA, respectively. Residual tensile stresses from ringtest were relaxed by approximately 61% and 64% of elastic shrinkage stresses due to SRA and EA, respectively, because of the tensile creep effect. Therefore, the creep effect should be considered to precisely estimate the restrained shrinkage behavior of concrete structures. The degree of restraint of UHPCC was approximately in the range of 0.78~0.85. The addition of combined EA and SRA showed minute influence on the degree of restraint. However, the effect decreased when thicker concrete ring was used. Tensile creep strains were measured and compared to the predicted values from 4-parametric prediction model considering time dependent restrained forces.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.641-650
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• 2010

The concrete cracking from the restrained stress caused by the shrinkage may play significant cause of deterioration of concrete structures by allowing the permeation of sulphate and chloride ions which in turn triggers corrosion of steel reinforcement. In particular, the cracking becomes more critical as water binder ratio (W/B) is reduced and concrete strength increases. Therefore, it needs to evaluate correctly the comprehensive shrinkage behavior of concrete with high strength: high-strength concrete (HSC), ultra-highstrength concrete (UHSC). The unrestrained shrinkage tests, however, cannot estimate the net shrinkage effectively which affects cracking after full development of strength and stiffness because it does not consider the degree of restraint, strength development, stress relaxation, and so on. Therefore, in this study, both free and restrained shrinkage tests with variables of W/B (W/B of 30, 25 and 16%) and admixtures (fly ash (FA) and granulated blast-furnace slag (BFS)) for HSC, very-high-strength concrete (VHSC) and UHSC were performed. The test results indicated that the autogenous shrinkage and total shrinkage at drying condition were reduced as W/B increased and FA, BFS were added, and the cracking behavior was suppressed as W/B increased and FA was added.

• 한국기계연구소 소보
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• s.17
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• pp.111-123
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• 1987

Two dimensional computer simulation of solidification behavior using FDM as simulation tool was applied to AI-bronze casting. By the comparison of computer simulation with the experimental results, it was showed that the final shrinkage position and solidification time are good accordance with results of computer simulation. It is expected that this software will be widely applied to casting design or rise ring for directional solidification.

• Journal of Power System Engineering
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• v.13 no.6
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• pp.95-101
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• 2009

The generator for gas turbine power generation consists of the rotor which generates magnetic field, the winding coil which is the path for the field current and the wedge and retaining ring which prevents the radial movement of the coil. Relatively severe deformation was observed at the coil end section during the inspection of the generator for peaking-load operation, and the thermal-electricity and the centrifugal force were evaluated by the simple modeling of the windings to find the cause. But the simulation stress was not sufficient to induce the coil plastic deformation. The analysis result seems to be applicable to the base-load generators which runs continuously without shut down up to a year, but there had been more deformation than simulated for the generator which is started up and shut down frequently. The cause of the coil deformation was the restriction of the expansion and shrinkage. The restriction occurs when the winding coil shrinks, and the stress overwhelms the yield stress and cause the plastic deformation. The deformation is accumulated during the start-ups and shut-downs and the thermal growth occurs. The factors which induce the coil restriction during the expansion and shrinkage should be reduced to prevent the unallowable deformation. The resolutions are cutting off the field current earlier during the generator shut-down, modifying the coil end section to remove the stress concentration and making the insulation plate inserted between the coil end section and the retaining ring have the constant thickness.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.483-488
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• 2016

The present study proposes an economical embedded ring-sensor that can measure a strain behavior of cement paste and mortar in early age. Using the proposed ring-sensor, the experimental method is proposed that can measure the setting time of the cement paste and mortar conveniently. The experimental study has been conducted using the mixtures of which W/C are 0.30, 0.35, 0.40, and 0.45. From the test result, the setting times measured by convectional test methods such as vicat method and penetration resistance method are compared with the setting time proposed by this study. The result reveals that the proposed ring-sensor can effectively measure the early age behavior so that can evaluate the time when the contraction starts. In addition, the contraction starting time can be regarded as a rational setting time, which is similar to the initial setting of convectional test methods.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.2 s.95
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• pp.87-94
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• 1999

The automated die design program is developed for cold forging of axisymmetric parts which are mainly produced by forward extrusion, backward extrusion, composite extrusion and upsetting. For this study, firstly classification of forged parts and investigation of die construction type usually employed in forging industry are carried out and the most proper type from several kinds of die construction is proposed as a standardized one. Based on the die design rules summarized in the references such as handbooks, technical papers, monthly journals, etc. the automated die design program was made using AutoLISP language available in AutoCAD software of personal computer. This program interactively runs for only input data, for example, forging process, shape of forged parts, type of punch, split of die insert and design of shrinkage rings and then displays details of drawings necessary to make a forging die. When a variety of forging processes and forged parts are tested to examine the validity of this program, it was confirmed to give good results applicable to the forging die design in press shop.

• Journal of the Korean Wood Science and Technology
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• v.43 no.1
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• pp.1-8
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• 2015

Relationship between annual ring width and physical properties of 24-year old alder woods (Alnus glutinosa L.) that had different seed origins from four provenances such as Bulgary, Italy, United Kindom, and Yugoslavia was investigated. No difference among different origins of seeds was found for the moisture content, density, and shrinkage or tangential radial (T/R) ratio. These properties had also no relationship with the growth rate. As important parameters among wood quality indices, no difference in the density or shrinkage on wood that has different growth rates was detected among alder woods from four different origins of seeds. Therefore, it is considered that higher growth rate might be a key factor for selecting the seed origin of the alder tree.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.5
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• pp.91-97
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• 2020

A split-die design for the cold forging of symmetric parts such as those having a hexagonal cross-section is presented in this paper. Parts with a hexagonal cross-section, such as bolt heads and nuts, should be forged with a die that has a hexagonal-shaped hole. A split type die is required to mitigate the buildup of stress concentrations located at the corners of the hexagonal hole. Generally, the insert of a hexagonal die is made by cutting each corner of a cylinder using a hexagonal hole and then combined with the die and shrink-fitted. However, split dies face problems when extruding material at the corners of the hexagonal split die. To address this problem, two types of split dies were evaluated: rounded hexagonal dies and angular hexagonal dies. The effects of the pre-stress ring on the dies were compared and analyzed and results show that using the angular split hexagonal die can extend the lifetime of forging dies.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.937-940
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• 2008

Recently, the recycling and reusing of construction and demolition waste concrete is urgently required because generation quantity of construction and demolition waste concrete is greatly increased according to the rapid increasing of urban redevelopment project. On the other hand, the problem solution for demand and supply unbalance of fine aggregate is urgently required because of the restriction of collecting sea fine aggregate by intensification of environment influence evaluation and the shortage of river fine aggregate. but a quality of aggregate as building structure is not demonstrated. Therefore it is the objective of this study to estimate plastic and early dry shrink crack of fiber reinforced concrete using a recycled aggregate by plat-ring test and mock-up test of exposure to the air. as a result, in case of plat- ring test, developing crack is wider using recycled aggregate concrete than natural aggregate concrete, is wider using fiber reinforced concrete than non fiber. in case of mock-up test of exposure to the air, it is similar to plat-ring test.

• Journal of the Korean Wood Science and Technology
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• v.10 no.3
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• pp.46-47
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• 1982

1. The physical and anatomical properties investigated in this study are the ones, which may give more effect on absorption of preservatives, such as variation of annual ring, specific gravity, shrinkage, E.M.C. of desorption and adsorption at 70 percent relative humidity condition, general and minute properties of wood. 2. On this study, the positive effects of wood structure, in particular, the appearances of tyloses in vessel element upon the absorption of creosote were observed. 3. Thirteen percent sodium chloride solution treatment and boiling hot water treatment have shown poor results to improve the preservative absorption characteristics of tested species however, some slight difference between treated and control could be seen. (see Tables 6 and 7).