• Nuclear Engineering and Technology
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• v.18 no.3
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• pp.218-227
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• 1986

Studies were conducted to determine the extent of oxidation and same of the mechanical property changes of Zircaloy-4 fuel cladding after it was exposed to hot steam environment. The purpose of these tests was to provide some informations on the embrittlement behavior of CANDU type fuel cladding, which could be experienced under the loss-of-coolant accident conditions. The Zircaloy fuel cladding tubes were exposed in a steam environment at the temperature of 90$0^{\circ}C$, 1,00$0^{\circ}C$. The growth of the ZrO$_2$ layer combined with an oxygen rich $\alpha$-phase layer into the Zircaloy tube material was found as a function of time t and temperature of steam exposure, E=1.1√Dt+0.002 where D is a temperature dependent diffusion coefficient. The tensile strength of the specimens exposed for a short period increased but decreased continuously with further exposure. The circumferential elongation was drastically changed with the exposure time while the hoop strength did't decrease greatly. The X-ray measurement of preferred orientation of the Zircaloy tube material indicated that grains in the as received tube were oriented such that the poles of the basal (0001) planes were predominantly radial, while the poles of the basal plane in the tube materials heattreated at 1,00$0^{\circ}C$ were oriented tangentially. It appears that this reoriented texture may contribute to lessening the decrease of the hoop strength of the heat treated Zircaloy tube material.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.369-379
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• 2012

The collapse of concrete structures by extreme loads such as impact, explosion, and blast from terrorist attacks causes severe property damage and human casualties. Concrete has excellent impact resistance to such extreme loads in comparison with other construction materials. Nevertheless, existing concrete structures designed without consideration of the impact or blast load with high strain rate are endangered by those unexpected extreme loads. In this study, to improve the impact resistance, the static and impact behaviors of concrete beams caste with steel fiber reinforced concrete (SFRC) with 0~1.5% (by volume) of 30 mm long hooked steel fibers were assessed. Test results indicated that the static and impact resistances, flexural strength, ductility, etc., were significantly increased when higher steel fiber volume fraction was applied. In the case of the layered concrete (LC) beams including greater steel fiber volume fraction in the tensile zone, the higher static and impact resistances were achieved than those of the normal steel fiber reinforced concrete beam with an equivalent steel fiber volume fraction. The impact test results were also compared with the analysis results obtained from the single degree of freedom (SDOF) system anaysis considering non-linear material behaviors of steel fiber reinforced concrete. The analysis results from SDOF system showed good agreement with the experimental maximum deflections.

• Polymer(Korea)
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• v.39 no.1
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• pp.64-70
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• 2015

Thermally expandable microcapsules (TEMs) can be expanded upon heating since the activation energy of liquid hydrocarbon at the core of the TEMs increased at high temperature. Due to this property, TEMs are widely used in the industry as blowing agents or light-weight fillers. In this article, chemical blowing agent and TEM were used for making polypropylene (PP) foams, and their mechanical properties were compared. Physical properties (tensile strength, impact strength etc.) of PP foams decreased with increasing the amount of blowing agents while weight of specimen decreased. However, PP foam produced with TEMs showed higher impact strength than the one with a chemical blowing agent. In order to figure out the difference of impact strength, the morphology of PP foamed was investigated. Expanding properties of TEM can be controlled by changing core back distance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.18-25
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• 2019

The cracks occurred during service life of concrete structure should be considered in durability design, because of the concrete's material property which is weak in tensile strength. In this study, the fly ash concrete mixtures considering 2 levels of strength is designed and outdoor exposure tests are conducted for those concrete specimens. The exposure environment is set to a splash zone, and in order to evaluate the effect of crack width on the behavior of chloride diffusion, the crack width of up to 1.0 mm is generated at intervals of 0.1 mm at each concrete mixture. After that, apparent chloride diffusion coefficient and surface chloride contents are deducted considering 3 levels of exposure periods(180 days, 365 days, 730 days). The diffusion coefficients of two types of mixture increase with the increase of crack width, and the diffusion coefficients decrease with the increase of exposure periods. In addition, the effect of the crack width on the diffusion coefficient is reduced as the exposure periods increase, which is attributed to the extra hydrate by chloride ion reducing the diffusivity of concrete. The behavior of the surface chloride contents does not significantly change by the increase in crack width, compared to the behavior of apparent chloride diffusion coefficient. Also, In the high strength FA concrete mixture, the surface chloride contents are 78.9 % ~ 90.7 % than the normal FA strength concrete mixture. Thus, Surface chloride contents have correlation with the strength of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.4
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• pp.335-344
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• 2014

The Quality of municipal solid waste incineration ash (incineration ash) was analyzed for the purpose of the reusing for concrete material. The folwability and strength properties of concrete mixed with incinerator ash were investigated. CaO component was included more than 50% in chemical component of incinerator ash, mean size of 50% accumulated particle distribution of incinerator ash was about $25{\mu}m$. Particle shape of incinerator ash ($IA_1$) was massed the round shape with fine particle, particle shape of incinerator ash ($IA_2$) was piled up the sheet shape according to manufacture procedure. The Quality of concrete was effected by use of incinerator ash. When the incinerator Ash ($IA_2$) was used, slum of concrete was increased and dosage of high range water reducing agent was reduced. However, strength development of concrete was decreased. Dosage of high range water reducing agent was increased by combined use of incinerator ash ($IA_2$) and diatomite powder, but strength development of concrete was improved. Ratio of compressive strength and tensile strength was in the range 85%~105% of CEB-FIP model code.

• Journal of the Korea Institute of Building Construction
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• v.15 no.1
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• pp.25-33
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• 2015

In this study, initial crack index was evaluated by FEM analysis to find the crack propagation from hydration heat in precast concrete. As results, as the usage of hardening accelerator increased, initial compressive strength increased and setting time was shortened. Additionally, as amounts of hardening accelerators increased, the central temperature of concrete increased and the time to reach the highest temperature was shortened. It was demonstrated that the hardening accelerators accelerated the hydration reaction of cement, and caused the increase of hydration heat within the short period of time. Furthermore, the crack index for evaluating the heat level was performed by FEM. As results, there was no problem about the cracks, despite of the growth of initial high hydration heat. This is because of the increased tensile strength that is large enough to sustain the thermally induced-stress.

• Korean Journal of Materials Research
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• v.2 no.1
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• pp.65-75
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• 1992

0.4wt%C steel added with V and/or Nb were forged and followed by air cooling. The structure-property relationships were examined and multiple regression analysis was conducted to quantify the magnitudes of effects of microalloying elements on the properties of the steels. All material's tensile strength are greater than $70kg/\textrm{mm}^2$, so they are equal to or superior to Q/T material's(S45C). Their impact energies are less than 40J, so they are 50% of Q/T material's. Increasing the content of V from 0.10 to 0.15 wt% had brought improvement in UTS about 20% but with some sacrifice of impact energy. These were the results from the precipitation strengthening by fine dispersion of VC in ferrite, increment of pearlite volume fraction and decrement of pearlite interlamellar spacings. However, increasing the content of Nb from 0.05 to 0.l0wt % slightly improved UTS and impact energy. NbC precipitates were more effective in suppression of austenite grain coarsening than VC precipitates. Combined additions of V+Nb were more effective to bring impact toughness than sole addition. Optimum combination of strength and toughness was accomplished wish 0.4C-1. 19Mn-0.05S-0.12V-0.07Nb steel.

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.218-222
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• 2000

W-Ti film properties for X-ray absorber applications have been investigated with Ti composition have been investigated with Ti composition variation. W-Ti films were deposited by DC magnetron sputtering system. As the working pressure increases, film density decreases and film stress changes from compressive to tensile. The transition pressure (where the film stress in zero) and the stress gradient decrease by adding Ti into W-Ti(6.5 at.%) film shows the smallest stress gradient and transition pressure. It also shows high density ($17.7g/\textrm{cm}^3$) similar to that of pure-W ($17.8g/\textrm{cm}^3$) at the transition pressure. All the films show columnar structure, and its size decreases with increasing Ti composition. Surface roughness and thermal stability are improved by Ti-addition, resulting in a better property for X-ray absorber applications.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.69-76
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• 2005

In this study, the high qualify recycled fine aggregate manufacturing system by the drying specific gravity separation method was evaluated. For the evaluation of the performance of the recycled aggregate, the engineering properties and durability of recycled aggregate has been tested. From the test results, the quality of recycled fing aggregates was improved by high quality recycled fine aggregate manufacturing system and satisfied with the quality standards of KS and JASS 5. Also, compressive and tensile strengths of recycled concrete show no critical difference caused by recycled fine aggregate replacement ratio. However, durability such as carbonation depth chloride ion penetration depth and drying shrinkage shows more deterioration than the concrete without recycled fine aggregate

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.709-716
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• 2005

The objective of this study is to develop a high ductile fiber reinforced mortar, ECC(Engineered Cementitious Composite) with using raw material commercially available in Korea. A single fiber pullout test and a wedge splitting test were employed to measure the bond properties in a matrix and the fracture toughness of mortar matrix respectively, which are used for designing mix proportion suitable for achieving strain-hardening behavior at a composite level. Test results showed that the properties tended to increase with decreasing water-cement ratio. A high ductile fiber reinforced mortar has been developed by employing micromechanics-based design procedure. Micromechanical analysis was initially peformed to properly select water-cement ratio, and then basic mixture proportion range was determined based on workability considerations, including desirable fiber dispersion without segregation. Subsequent direct tensile tests were performed on the composites with W/C's of 47.5% and 60% at 28 days that the fiber reinforced mortar exhibited high ductile uniaxial tension property, represented by a maximum strain capacity of 2.2%, which is around 100 times the strain capacity of normal concrete. Also, compressive tests were performed to examine high ductile fiber reinforced mortar under the compression. The test results showed that the measured value of compressive strength was from 26MPa to 34 MPa which comes under the strength of normal concrete at 28 days.