• Computers and Concrete
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• v.15 no.4
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• pp.485-501
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• 2015

Cooling by the flow of water through an embedded cooling pipe has become a common and effective artificial thermal control measure for massive concrete structures. However, an extreme thermal gradient induces significant thermal stress, resulting in thermal cracking. Using a mesoscopic finite-element (FE) mesh, three-phase composites of concrete namely aggregate, mortar matrix and interfacial transition zone (ITZ) are modeled. An equivalent probabilistic model is presented for failure study of concrete by assuming that the material properties conform to the Weibull distribution law. Meanwhile, the correlation coefficient introduced by the statistical method is incorporated into the Weibull distribution formula. Subsequently, a series of numerical analyses are used for investigating the influence of the correlation coefficient on tensile strength and the failure process of concrete based on the equivalent probabilistic model. Finally, as an engineering application, damage and failure behavior of concrete cracks induced by a water-cooling pipe are analyzed in-depth by the presented model. Results show that the random distribution of concrete mechanical parameters and the temperature gradient near water-cooling pipe have a significant influence on the pattern and failure progress of temperature-induced micro-cracking in concrete.

• Progress in Superconductivity and Cryogenics
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• v.11 no.4
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• pp.12-15
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• 2009

The $I_c$ degradation behavior of critical current in differently processed YBCO and SmBCO CC tapes with IBAD template has been investigated. It has been known that the residual strain in the CC tape will influence the shape of the $I_c$-strain window; $I_c$ may show a peak value if there exist a residual strain induced in the tape during manufacturing. The difference of residual strain may be resulted from the adopted different deposition techniques. In this study, bending test of CC tapes has been done using the Goldacker bending test rig which can produce both compressive and tensile bending strain continuously or alternately to the sample. For SmBCO CC tapes, in continuous compressive bending test, $I_c$ showed a minimal increase and did not degrade up to the largest strain that can be applied using the bending rig equivalent to 1.15% based on the sample thickness. However, in the case of alternate application of compressive and tensile bending strain, $I_c$ showed a larger degradation and a lower reversible limit when compared with the case of continuous application of the bending strain. When $I_c$ started to degrade significantly at the tension side, the reversibility ended, also at the compression side which is resulted from the permanent deformation like delamination or cracks that was induced due to tensile bending strain.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.2
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• pp.25-30
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• 2015

This study involved the fabrication of precision machine tools using a polycrystalline diamond tip [sintered PCD and cemented carbide (WC-Co) tip] and WC-Co shanks via diffusion bonding with a paste-type nickel alloy filler metal. Diffusion bonding is a process whereby two materials are pressed together at high temperature and high pressure for a sufficient period of time to allow significant atomic diffusion to occur. For smooth progress, a filler metal of nickel alloy was used at the interface. Optical microscopy images were used to observe the copula of the bonded layer. It was confirmed that cracks occurred near the junction in all cases. The tensile strength of the bond was measured using a universal testing machine (UTM) with WC-Co proportional test specimens.

• Progress in Superconductivity and Cryogenics
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• v.7 no.2
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• pp.11-15
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• 2005

The I$_{c}$ degradation behavior of Bi-2223 tapes bent at RT and 77K were investigated using the bending device invented by Goldacker. Test results on fixing the tape at RT and 17K showed no difference. At 17K and RT bending, the critical strain was 0.67 and 0.50$\%$, respectively, for the VAM-l tape. For the AMSC tape, it was 0.94 and 0.88$\%$, respectively. These results show that there is additional residual stress in the superconducting filaments to be bent at 17K which shifts the formation of cracks into smaller bending radii. This was proved by computational analysis based on the mixture rule of composites. For the VAM-l tape, the Ie degradation behavior using the Goldacker type device shifted to higher strain levels at about 0.5$\%$, as compared with the FRP sample holders which have a critical bending strain of about 0.24$\%$. Also, for the externally reinforced AMSC tape, Ie degradation using the Goldacker type device begins at a higher strain level, at 0.88$\%$ as compared with using FRP sample holders, at 0.74$\%$. The difference between both cases can be explained by the tensile' and thermal stresses that the tapes were subjected to during fixing (soldering) when the FRP sample holders were used.

• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.24-28
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• 2013

In this study, the homogeneity of critical current, $I_c$, along the lengthwise direction in the coated conductor (CC) tape under uniaxial tension was investigated using a multiple voltage tap configuration. Initially, a gradual and homogeneous $I_c$ degradation occurred in all subsections of the tape up to a certain strain value. This was followed by an abrupt $I_c$ degradation in some subsections, which caused scattering in $I_c$ values along the length with increasing tension strain. The $I_c$ degradation behaviour was also explained through n-value as well as microstructure analyses. Subsections showed $I_c$ scattering corresponding to damaged areas of the CC tape revealed that transverse cracks were distributed throughout the gauge length. This homogeneous $I_c$ degradation behaviour under tension is similar with the case under torsion strain but different with the case under hard bending which were previously reported. This behaviour is also different with the case using Bi-2223 HTS tapes under tension strain.

• Journal of Korean Society for Geospatial Information Science
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• v.17 no.1
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• pp.105-111
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• 2009

A construction can be more convenient and safer with adequate informations. Consequently, studies on collecting various informations using newest surveying technology and applying these informations to a construction have been making progress recently. Digital images are easy to obtain and contain various informations. Therefore, with the recent development of image processing technology, the application field of digital images is getting wider. In this study, we proposed to use a fisheye lens camera in underground construction sites, especially tunnels, to overcome inconvenience in photographing with general lens cameras. A program for mapping the surface of a tunnel and making a mosaic image is also developed. This mosaic image can be applied to observe and analyze abnormal phenomenons on tunnel surface like cracks, water leakage, exfoliates, and so on.

• Magazine of the Korean Society of Agricultural Engineers
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• v.22 no.4
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• pp.82-95
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• 1980

This paper complies the results of the studies so far made on the subsoil improvement of subsurface drainage systems for wet paddy fields (those were located in the Gum-Ho area in Kyung Buk province) which had poor permeability and a high water table. In general, a drainage problem is an excess of water on the ground surface which can effect the productivity and bearing capacity of the soil. With drain pipe systems, (According to their depths and spacing) it may be possible to correct that problem. The experimentation consisted of three test plots, two of which included drain pipe systems with varing depths and width spacing of the pipes. The third plot (C) was an ordinary plot being exempt of a drain pipe system. In detail, the depth of plot A was 80 cm, and the width spacings began at 2. Om and increased by 2. Om up to 10. 0m. The depth of plot B was 60cm and the width spacing was the same as plot A. These tests were performed to research specific details; such as crop yeild, bearing capacity of the soil, the amount of underdrainage, surface cracks, root distribution, the water table level, the consumptive water depth and the soil moisture content. The test period lasted three years, from 1977 thru 1979. The results obtained were as follows: 1. During the test period, the weather conditions for the area tested were in accordance with the annual average for that area. Furthermore the precipitation factor during the spring cultivation season, the intermediate drainage period and the harvest drainage period was of optimum conditions for controling surface cracks, because of less precipitation than evaporation. 2. The difference in the level of the ground water table in plots A and B was hardly noticable, but the difference in the test plots and the ord. plot was greatly noticable. The test plots (A, B) were 30 to 40cm lower than the ordinary plot. On the whole, the ground water table of the ord. plot always stayed at a level of 15-20cm beneath the surface of the soil, the ground water table of the test plot A showed The difference in the depth of the pipe lower than the test plot B, while the test plots showed a remarkable descending effect. 3. The soil temperature in plot A was slightly core than in plot B with a difference of 0. 47$^{\circ}$C, but plot A was 1. 6$^{\circ}$C higher than the ord. plot during the flooding period, but after drainage the temperature difference climed to 2. 0$^{\circ}$C. 4. During the 3rd test year, the values of the cracks were recorded with the values of 59cm in plot A, 42cm in plot B and 15cm in the ordinary plot. Plots A and B had increased 2.5 times the value of the first year while the ordinary plot had remained the same. 5. The root weight of the rice was measured at a value of 77.2 gr. for plot A, 73.5 gr. for plot B and 65.3 gr. for the ord. plot. Therefore, the root growths in plots A and B were much more energetic than in the ord. plot. 6. The consumptive water depth measured during the 3rd year resulted in the values of 26. 0mm per day for plot A, and 24.9 mm per day for plot B, respectively. Therefore, both plot A and plot B maintained the optimum consumptive water depths, but the ordinary plot only obtained the value of 12.3 mm per day, which clearly showed less than the optimum consumptive water depth which is 20 to 30 mm/day. 7. The soil moisture content is in direct relationship to the ground water level. During drainage, test plot A decreased in its ground water level much more rapidly than the other two plots. Therefore, plot A had a much less soil moisture content. But this decreased water level could be directly effected by the weather conditions. 8. The relationship between the bearing capacity and the soil moisture content were directly inversely proportional. It can be assumed that the occurence of soil creaks is limited by the soil moisture content. Therefore, the greater the progress of the surface creaks resulted in a greater bearing capacity. So, tast plot A with a greater amount of surface cracks than the other test plots resulted in a greater bearing capacity. But, the bearing capacity at the harvest season could be effected by the drainage during the intermediate drainage period and by the weather conditions. 9. Comparing the production of the test plots to the ord. plot; there was an increased value of 840kg for plot A, 755kg for plot B and 695kg for the ord. plot in the rough rice. Therefore, plot A had an increase of 20% over the ordinary plot. The possibility of producing double crops was investigated. The effects on barley production in the test plots showed a value of 367kg per 10 acres, which substantiated the possibility of double crops because that value showed an increased value over the average yearly yield for those uplands. 10. So as a result, it can be recommended that by including a drain pipe system with the optimum conditions of an (80cm centimeter) depth and a (l0m) spacing will have a definite positive effect on the over all production capacity and quality of wetpaddy fields.

• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.125-132
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• 2018

In this study, a direct tensile test was planned to identify the tensile performance of UHPC, and the irregularity of cracks, which is a problem of the direct tensile test, was complemented through the introduction of notches at the center of a specimen. In this regard, a number of specimens divided by batch to reduce the deviation of direct tensile test values were fabricated to present reference data with respect to highly reliable direct tensile strength values. In addition, the mechanical properties and reliability of the specimens were examined under the curing conditions of the specified design strength of 120MPa for the steel fiber reinforced concrete with 1.5% fiber volume fraction, which is most suitable for the field application. As a result, the deviation of averages by batch between compressive strength and direct tensile strength did not show a large difference, and all cracks occurred within 20mm in the direct tensile test. At the 95% confidence interval of the direct tensile strength, the range was considerably small in the mean and the standard deviation, and there was no significant difference depending on the curing conditions. The results confirmed that a stable direct tensile test was performed, and highly reliable results were obtained through the fabrication of specimens by batch and test progress.

• Progress in Superconductivity
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• v.9 no.1
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• pp.68-73
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• 2007

We fabricated the in-situ $MgB_2$ wires using the powder-in-tube method and investigated the effects of sintering temperature and SiC contents on the microstructure and superconducting properties. Pure $MgB_2$ wires and 5, 10, 20 wt.% SiC doped $MgB_2$ wires were sintered at $600-1000^{\circ}C$ for 30 minutes in Ar atmosphere. We found that $MgB_2$ phase was mostly formed at the sintering temperature of $700^{\circ}C$ and above, and the critical temperature ($T_c$) increased with increasing sintering temperature. For the $MgB_2$ sintered at $850^{\circ}C$, the highest critical current density ($J_c$) was obtained to be $3.7{\times}10^5\;A/cm^2$ at 5 K and 1.6 T by a magnetic properties measurement system (MPMS). The addition of SiC to the $MgB_2$ wires changed microstructure and critical properties. SEM observation showed that the $MgB_2$ core had considerable micro-cracks in undoped wire and the density of micro-cracks decreased with increasing SiC contents. The critical temperature decreased as the SiC contents increased, on the other hand, the critical current density of SiC doped $MgB_2$ wires in high magnetic field was enhanced compared to that of undoped $MgB_2$ wires.

• Computers and Concrete
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• v.26 no.4
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• pp.367-375
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• 2020

Today, the use of special technologies in the admixture of concrete has made tremendous progress, but the problem that has always existed in the construction of concrete members is the brittleness and lack of loading bearing after cracking, which leads to reduced strength and energy absorption. One of the best ways to fix this is to reinforce the concrete with steel fibers. Steel fibers also control cracks due to dry shrinkage, reduce structural crack width, and improve impact resistance. In this study, recycled steel fibers from worn tires have been used in the manufacture of concrete samples, the secondary benefits of which are the reduction of environmental pollution. One of the disadvantages of steel fiber reinforced concrete is the corrosion of steel fibers and their deterioration in harsh environments such as coastal areas. Corrosion caused by chlorine ions in metal fibers causes deterioration and early decommissioning of structures in corrosive environments. In this study, the effect of the dosage of steel fibers (dosages of 15, 30, and 45 kg of fibers per cubic meter of concrete) and aspect ratio of fibers (aspect ratio of 25 and 50) on compressive and flexural strength of concrete samples are investigated. In the following, the effect of fiber corrosion on the results of the mechanical properties of concrete samples is examined. The results show that the increase in fiber causes a relative increase in compressive strength, and a significant increase in flexural strength, and corrosion of steel fibers without reducing workability reduces compressive strength and flexural strength by up to 6 to 11%, respectively.