• Land and Housing Review
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• v.3 no.1
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• pp.83-88
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• 2012

In this study, physical characteristics of cement and/or concrete materials that are typically used for energy-foundation (EF) structures have been studied. The thermal conductivity and structural integrity of the cement-based materials were examined, which are commonly encountered in backfilling a vertical ground heat exchangers, cast-in-place concrete piles and concrete lining in tunnel. For this purpose the thermal conductivity and unconfined compression strength of cement-based materials with various curing conditions were experimentally estimated and compared. Hydration heat generated from massive concrete in the cast-in-place concrete energy pile was observed for 4 weeks to estimate its dissipation time in the underground. The hydration heat may mask the in-situ thermal response test (TRT) result performed in the cast-in-place concrete energy pile. It is concluded that at least two weeks are needed to dissipate the hydration heat in this case. In addition, a series of numerical analysis was performed to compare the effect of thermal property of the concrete material on the cast-in-place pile.

• Journal of the Korean Society of Clothing and Textiles
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• v.25 no.10
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• pp.1809-1820
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• 2001

본 연구에서는 모 직물의 접착심과의 접착 후, 프레싱 처리 후, 드라이클리닝 처리 후 프레스로 처리한 실제의 의복의 관리와 생산 면에서 접할 수 있는 직물 변화에 대하여 물성 변화를 살펴보았다. 겉감으로는 신사복 춘하용 모 100% 또는 모혼방 직물 15종류를 사용하였으며 심지로는 신사복에 많이 쓰이는 3종류 심지를 사용하였다. KES시스템을 이용하여 직물의 접착후, 프레싱 처리 후, 드라이크리닝과 프레싱 처리 후의 물성 변화를 시험하였으며 다음과 같은 결과를 얻었다. 1) 접착 후 EM은 대체로 감소하지만 강성과 이력 현상은 증가하는 것으로 나타났다. 결과로 KOSHI, SHARI, HARI는 증가하고 THV는 감소하여 태는 접착으로 저하되었다. 2) 프레싱 처리 후는 접착 후와 큰 차이를 보이지 않는다. 마찰특성에서 좀더 매끄러워지고 마찰 계수는 증가하는 것으로 나타났다. 3) 드라이크리닝과 프레싱 처리 후의 물성의 변화에서는 위사 방향의 큰 값을 갖는 경우에 감소하는 것으로 나타났다. 굽힘 강성과 전단강성은 감소하였지만 이력은 증가하는 흥미로운 결과를 보인다. 드라이클리닝 용제의 효과로 여겨진다. 무게는 증가하여 직물이 처리 후 수축한 것으로 나타났다. 프레싱 처리 후와 비교시 KOSHI, SHARI, HARI와 FURAMl는 감소하고 THV는 증가하여 태가 향상하였다.

• Design & Manufacturing
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• v.11 no.3
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• pp.25-28
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• 2017

The production of carbon fiber reinforced thermoplastics(CFRTP) parts using an injection/compression molding process that differs from the conventionally used fabrication methods was investigated Before the application of composite molding in the injection/compression molding process, a simple compression molding experiment was performed using a hydraulic press machine to determine the characteristics of resin impregnation and to obtain a basic physical property data for the CFRTP. Based on these results, injection/compression molded specimens were manufactured and an additional insert/over molding process was applied to improve the impregnation rate of the molded specimens. The results demonstrated that the tensile strength of the molded parts using the faster injection/compression process was similar to that of a hydraulic press molded product.

• Composites Research
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• v.19 no.6
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• pp.1-7
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• 2006

This is the preliminary study to develop composite window frame of commercial aircraft using VaRTM process. For two candidate carbon fabrics(triaxial overbraid, sleeving braider), specimens were fabricated using VaRTM process, and the physical & mechanical property tests were performed to obtain the material properties according to ASTM. FEM analysis for each candidate carbon fabric was performed to find the minimum number of plies and weight for composite window frame to satisfy the design requirements. In this study, Tsai-Wu strength failure criterion was used to evaluate the safety of structure.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2147-2157
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• 2023

The aggregate-forming minerals in concrete undergo volume swelling and microstructure change under neutron irradiation, leading to degradation of physical and mechanical properties of the aggregates and concrete. A comprehensive investigation of volume change and elastic property variation of major aggregate-forming minerals is still lacking, so molecular dynamics simulations have been employed in this paper to improve the understanding of the degradation mechanisms. The results demonstrated that the densities of the selected aggregate-forming minerals of similar atomic structure and chemical composition vary in a similar trend with deposited energy due to the similar amorphization mechanism. The elastic tensors of all silicate minerals are almost isotropic after saturated irradiation, while those of irradiated carbonate minerals remain anisotropic. Moreover, the elastic modulus ratio versus density ratio of irradiated minerals is roughly following the density-modulus scaling relationship. These findings could further provide basis for predicting the volume and elastic properties of irradiated concrete aggregates in nuclear facilities.

• Membrane Journal
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• v.33 no.1
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• pp.1-12
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• 2023

In this review, surface modification methods of hydrophobic poly(tetrafluoroethylene) (PTFE) membrane are introduced and their improved hydrophilicity results are discussed. Fluoropolymer based membranes, represented by PTFE membranes have been used in various membrane separation processes, including membrane distillation, oil separation and gas separation. However, despite excellent physical properties such as chemical resistance, heat resistance and high mechanical strength, the strong hydrophobicity of PTFE membrane surface has become a challenging factor in expanding its membrane separation application. To improve the separation performance of PTFE membranes, wet chemical, hydrophilic coating, plasma, irradiation and atomic layer deposition are applied, modifying the surface property of PTFE membranes while maintaining their inherent properties.

• The Journal of Engineering Geology
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• v.26 no.3
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• pp.383-392
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• 2016

This study is to evaluate the physical and mechanical properties on the Ipseok-dae columnar joints of Mt. Mudeung National Park. For these purposes, physical and mechanical properties as well as discontinuity property on the Mudeungsan tuff, measurement of vibration and local meteorology around columnar joints, and ground deformation by self-weight of columnar joints were examined. For the physical and mechanical properties, average values were respectively 0.65% for porosity, 2.69 for specific gravity, 2.68 g/cm³ for density, and 2411 m/s for primary velocity, 323 MPa for uniaxial compressive strength, 81 GPa Young's modulus, and 0.25 for Poisson's ratio. For the joint shear test, average values were respectively 3.15 GPa/m for normal stiffness, 0.38 GPa/m for shear stiffness, 0.50 MPa for cohesion, and 35° for internal friction angle. The JRC standard and JRC chart was in the range of 4~6, and 1~1.5, respectively. The rebound value Q of silver schmidt hammer was 57 (≒ 90 MPa). It corresponds 20% of the uniaxial compressive strength of intact rock. The maximum vibration value around the Ipseok=dae columnar joints was in the range of 0.57 PPV (mm/s)~2.35 PPV (mm/s). The local meteorology of surface temperature, air temperature, humidity, and wind on and around columnar joints appeared to have been greatly influenced the weather on the day of measurement. For the numerical analysis of ground deformation due to its self-weight of the Ipseok-dae columnar joints, the maximum displacement of the right ground shows when the ground distance is approximately 2 m, while drastically decreased by 2~4 m, thereafter was insignificant. The maximum displacement of the middle ground shows when the ground distance is approximately 0~2 m, while drastically decreased by 3~10 m, thereafter was insignificant. The maximum displacement of the left ground shows when the ground distance is approximately 5~6 m, while drastically decreased by 6~10 m, thereafter was insignificant.

• Journal of the Korean Geotechnical Society
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• v.22 no.6
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• pp.27-40
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• 2006

Damage of cut-and-cover tunnel lining can be attributed to physical and mechanical factors. Physical factors include material property, reinforcement corrosion, etc. while mechanical factors include underground water pressure, vehicle loads, etc. This study is limited to the modeling of rigid circular cut and cover tunnel constructed at a depth of $1.0{\sim}1.5D$ in loose sandy ground and subjected to a vibration frequency of 100 Hz. In this study, only damages due to mechanical factors in the form of additional loads were considered. Among the different types of additional, excessive earth pressure acting on the cut-and-cover tunnel lining is considered as one of the major factors that induce deformation and damage of tunnels after the construction is completed. Excessive earth pressure may be attributed to insufficient compaction, consolidation due to self-weight of backfill soil, precipitation and vibration caused by traffic. Laboratory tunnel model tests were performed in order to determine the earth pressure acting on the tunnel lining and to investigate the applicability of existing earth pressure formulas. Based on the difference in the monitored and computed earth pressure, a factor of safety was recommended. Soil deformation mechanism around the tunnel was also presented using the picture analysis method.

• Korean Journal of Materials Research
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• v.15 no.4
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• pp.217-223
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• 2005

Thermal, electrical and mechanical properties of high purity niobium and tantalum refractory rare metals were investigated tn evaluate the physical purity. Higher purity niobium and tantalum metals showed lower hardness due to smaller solution hardening effect. Temperature dependence of electrical resistivity showed a typical metallic behavior. Remarkable decrease in electrical resistivity was observed for a high purity specimen at low temperature. However, thermal conductivity increased for a high purity specimen, and abrupt increase in thermal conductivity was observed at very low temperature, indicating typical temperature dependence of thermal conductivity for high purity metals. It can be known that reduction of electron-phonon scattering leads to increase in thermal conductivity of high purity niobium and tantalum metals at low temperature.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.338-344
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• 2018

The lunar surface temperature is important as a environmental parameter for the thermal design of the lunar exploration vehicles such as orbital spacecraft, lander, and rovers. In this study, the temperature is numerically predicted through a simplified lumped system model for the energy conservation. The physical values required for the analysis of the energy equation are derived by considering the geometric shape, and the values presented in the previous research results. The areal specific heat, which is the most important thermo-physical property of the lumped system model, was extracted from the temperature measurements by the Diviner loaded on the LRO, and the value was predicted by calibration of the analytical model to the measurements. The predicted temperature distribution obtained through numerical integration has sufficient accuracy to be applied to the thermal design of the lunar exploration vehicles.