• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.17-24
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• 2018

The pullout test, a nondestructive testing(NDT), for pre-installed inserts is perhaps the most widely used technique to estimate the in-situ compressive strength of concrete. It measures the force needed to pullout a standardized metal insert embedded into concrete members. The pullout test was certified by the American Society for Testing and Materials(ASTM) and Canadian Standards Association(CSA) as a reliable method for determining the strength of concrete in concrete structures under construction. To easily estimate the strength of ultra-high-strength concrete, a simplified pullout tester, primarily composed of a standard 12mm bolt with a groove on the shaft as a break-off bolt, an insert nut, and a hydraulic oil pump without a load cell, was proposed. Four wall and two slab specimens were tested for two levels of concrete strength, 80MPa and 100MPa, using a simplified pullout tester with a load cell to verify the advantages of the pullout test and simplified pullout test. The compressive strength of concrete, pullout load, and the rupture of the break-off bolt were measured 11 times, day 1 to 7, 14, 21, 28, and 90. The correlation of the pullout load and the compressive strength of each specimen show a higher degree of reliability. Therefore, a simplified pullout test can be used to evaluate the in-place strength of ultra-high-strength concrete in structures. The prediction equation for the groove diameter of the break-off bolt(y) with the concrete strength(x) was proposed as y=0.0184x+5.4. The results described in this research confirm the simplified pullout's utility and potential for low cost, simplicity, and convenience.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.688-695
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• 2011

This study was carried out for some survey about soil compaction in the multi-cropping system of paddy field. Investigated sites were 90 farmer's fields in south-eastern part of Korea. The tillage practices season was different according to cropping system of paddy; in spring for mono rice cultivation and in autumn for the multi-cropping field. The average tillage depth in investigated sites was about 25 cm, however, it is different between the farmer's tillage practices and soil characteristics. It is high correlation to tillage deep and minimum resistance of penetration. The reaching soil deep to maximum resistance of penetration was about 27 cm, and average penetration resistance of the deep is 1.8~2.0 MPa for moderately fine-textured soils and more than 3.0 MPa for moderately coarse-textured soils. The difference of penetration resistance between cultivating and compacted layer was in order to sandy loam > clayey loam > clayey, and the difference was lesser in poorly drained soils than somewhat poorly ones. In the rice mono cropping field, the maximum resistance in no-tillage for 15 years was 1.18~1.25 Mpa at 20~25 cm in soil deep, however, the resistance of field with every year tillage practices was 2.03~2.21 Mpa. In the extremely compacted sandy loam textured soils, the penetration resistance at 30 cm in soil depth was drastically reduced by the subsoil from 5.2 Mpa to 3.2 Mpa, and the watermelon root in plastic film house was deep elongated.

• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.99-104
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• 2016

High purity Si-C (99.999%) powder prepared by mechanical alloying was added to a commercial SiC powder as a sintering additive. Reaction bonded silicon carbide balls and jars with high purity (99.98%) were used for the mechanical alloying. As a result, the purity of the sintered Si-C was higher than 99.99%. When sintered at $2200^{\circ}C$ under 50 MPa pressure for 1 h, SiC containing 10 wt% of high purity Si-C showed a relative density of 95.3%, similar to the relative density of commercial SiC (95%). However, the relative density of SiC decreased to 90.6% without the additive when the applied pressure decreased to 40 MPa. In contrast, the relative density was nearly unaffected by the decrease of the pressure when using the Si-C additive. Therefore, the addition of Si-C powder promoted the densification of SiC above $2000^{\circ}C$ under 40 MPa pressure.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.04a
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• pp.79-80
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• 2006

새로운 급속소결방법인 고주파유도가열 소결법과 펄스전류활성 소결법을 이용하여 습식 볼밀링으로 혼합한 WC-8wt.%Co분말에 60MPa의 압력과 90%의 고주파출력 또는 2800A의 필스전류를 가하여 상대밀도가 98.6% 이상인 초경재료를 2분이내의 짧은 시간에 제조하였다. 초기의 WC분말의 입도가 미세해짐에 따라 고주파유도가열 소결법과 펄스전류활성 소결법 모두 소결시간이 단축되는 경향을 보였으며 그 소결체의 결정립 크기도 감소하였다. 고주파유도가열 소결법으로 제조된 초경합금의 WC 결정립 크기는 초기입도가 증가함에 따라 가각 410, 540, 600, 700 및 850nm으로 측정되었으며. 그 결과를 Fig. 1.에 나타내었다. WC의 초기입도가 $0.5{\mu}m$일 경우 고주파유도가열 소결법과 펄스전류활성 소결법으로 제조된 WC-8wt.%Co 소결체의 경도와 파괴인성은 각각 $1923kg/mm^2$과 $10.5MPa{\cdot}m^{1/2}$ 및 $1947kg/mm^2$과 $10.8MPa{\cdot}m^{1/2}$ 이었다.

• Journal of ILASS-Korea
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• v.18 no.2
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• pp.73-80
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• 2013

The purpose of this study was compared the spray, combustion and emissions (NOx, CO, HC, smoke) characteristics of a typical fuel (100% Diesel, DME) and Diesel-DME blended fuel in a Constant Volume Chamber (CVC) and a single-cylinder DI diesel engine. Spray characteristics were investigated under various ambient and fuel injection pressures when the Diesel-DME blended ratio is varied. The parameters of spray sturdy were spray shape, penetration length, and spray angle. Common types of injectors having seven holes and made by Bosch were used. As of use, the typical fuel (100% Diesel, DME) and the blended fuel by mixture ratio 95:5, 90:10 (Diesel:DME) were used. The Injection pressure was fixed by 70.1MPa, when the ambient Pressure was varied 0.1, 2.6 and 5.1 MPa. The combustion experiments was conducted with single cylinder engine equipped with common rail injection system. injection pressure is 70 MPa. The amount of injected fuels is adjusted to obtain the fixed input calorie value as 972.2 J/cycle in order to compare with the fuel conditions.

• Geomechanics and Engineering
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• v.13 no.3
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• pp.431-446
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• 2017

Rock bridges in rock masses would increase the bearing capacity of Non-persistent discontinuities. In this paper the effect of ratio of rock bridge surface to joint surface, rock bridge shape and normal load on failure behaviour of intermittent rock joint were investigated. A total of 42 various models with dimensions of $15cm{\times}15cm{\times}15cm$ of plaster specimens were fabricated simulating the open joints possessing rock bridge. The introduced rock bridges have various continuities in shear surface. The area of the rock bridge was $45cm^2$ and $90cm^2$ out of the total fixed area of $225cm^2$ respectively. The fabricated specimens were subjected to shear tests under normal loads of 0.5 MPa, 2 MPa and 4 MPa in order to investigate the shear mechanism of rock bridge. The results indicated that the failure pattern and the failure mechanism were affected by two parameters; i.e., the ratio of joint surface to rock bridge surface and normal load. So that increasing in joint area in front of the rock bridge changes the shear failure mode to tensile failure mode. Also the tensile failure change to shear failure by increasing the normal load.

• Journal of Practical Agriculture & Fisheries Research
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• v.21 no.1
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• pp.41-48
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• 2019

This study was carried out to establish a proper cultivation site and to diagnose the drought tolerance of Oplopanax elatus leaves by using pressure-volume curves. As a result of analysing data measured, the leaf of Oplopanax elatus showed the osmotic pressure at full turgor(Ψosat) was -0.77 MPa, and the osmotic pressure at incipient plasmolysis(Ψotlp) was -0.90 MPa. Then, the value of maximum bulk modulus of elasticity Emax was 3.7 MPa, showing that slightly lower drought tolerance of Oplopanax elatus. Furthermore, the values of relative water contents RWCtlp and RWC^* were above 80%, showing that the function of osmoregulation is somewhat better. Thus, responses to water relations such as Ψosat, Ψotlp, Emax, RWCtlp and RWC^* of Oplopanax elatus showed relatively lower drought-tolerance property indicating that those growth are appropriate in high moisture soil sites.

• Journal of Technologic Dentistry
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• v.37 no.3
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• pp.121-127
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• 2015

Purpose: This study was intended to investigate the effect of applying liner for chemical bonding and physical surface roughness created on zirconia by using a sandpaper before sintering on the bond strength between the two materials. Methods: Zirconia blocks were cut using a low-speed cutter. Plate-shaped specimen($6mm{\times}6mm{\times}3mm$) was fabricated by sintering after giving surface roughness according to four kinds of sandpapers. Depending on whether or not to use liner, 60 specimens were divided into two groups ZN(non-liner), ZL(liner), and the two groups were subdivided into four groups respectively in accordance with sandpaper used, totaling eight groups (n=10). The surface roughness (Ra) values and shapes before sintering were observed, and shear bond strength after pressing ceramic plasticity was measured with a universal testing machine. For a test of the significance, a one-way ANOVA was performed, and Tukey's multiple comparison test was conducted. Results: The observation of the surface roughness was SB04($2.22{\pm}1.16{\mu}m$), SB08($2.98{\pm}0.33{\mu}m$), SB12($2.44{\pm}1.32{\mu}m$), SB20($2.34{\pm}0.59{\mu}m$) and SA04($2.34{\pm}0.67{\mu}m$), SA08($1.28{\pm}0.90{\mu}m$), SA12($2.03{\pm}1.60{\mu}m$), SA20($2.19{\pm}1.73{\mu}m$). In the case of ZN Group, the shear bond strength was ZN04($23.26{\pm}3.83MPa$), ZN08($21.76{\pm}2.33MPa$), ZN12($20.49{\pm}3.01MPa$), ZN20($24.98{\pm}4.22MPa$)(p<0.05). As for ZL Group, the shear bond strength was ZL04($25.09{\pm}5.67MPa$), ZL08($22.98{\pm}2.26MPa$), ZL12($21.54{\pm}5.70MPa$), ZL20($23.98{\pm}3.23MPa$)(p<0.05). Conclusion: The research results showed that the bond strength of Zirconia core and Pressing ceramic was further improved by physical surface treatment before sintering, rather than by chemical bonding through liner surface treatment.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.577-585
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• 1992

TiB2 and TiC were prepared from the mixture of metal titanium, boron and graphite powders in Argon atmosphere by Self-propagating High-temperature Synthesis method. The sintered properties of TiB2-TiC composite as a function of TiC content and sintering temperature were investigated in TiB2 matrix. The sintered properties were the most excellent at 10 wt% TiC content in TiB2-TiC composite. The relative density, M.O.R strength, hardness and fracture toughness of TiB2-10 wt% TiC composite sintered at 190$0^{\circ}C$ for 90 min by hot-pressing under the pressure of 30 MPa were 98.6%, 634 MPa, 2128.1 kg/$\textrm{mm}^2$ and 4.09 MN/m3/2, respectively.

• Tunnel and Underground Space
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• v.7 no.4
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• pp.293-298
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• 1997

Permeability was not represented as a simple function of the difference between confining pressure($P_c$) and pore pressure($P_p$). The effective pressure($P_e$) for measurements of the permeability is shown to be $P_c-{\alpha}P_p$, where $\alpha$ is a coefficient of effective pressure. Local values of $\alpha$ were determined at intervals along the pressure path which range 25MPa to 55MPa. The values of $\alpha$ ranged 0.65 to 1.09 for Pocheon granite and 1.20 to 1.43 for Wonju granite. Also, the value of $\alpha$ calculated by the cross-plotting method was 0.90 for Pocheon granite, 1.59 for Wonju granite and 4.35 for jointed Pocheon granite. $\alpha$ was found to be stress-history dependent.