• Journal of Korea Foundry Society
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• v.27 no.6
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• pp.258-262
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• 2007

단섬유강화 고분자 복합재료의 고온압축 프레스 성형 시 유리섬유의 유동을 지배하는 인자인 유리섬유와 모재의 유동성에 관하여 연구하기 위하여 ?h트 스트랜드의 교차각도를 $30^{\circ},\;45^{\circ},\;60^{\circ}$로 배향하여 모재와 적층시킨 다음 열압축프레스를 사용하여 1차로 시트를 제작하고, 이 제작된 시트를 가열로로 가열하여 열압축프레스로 2차 고온압축 프레스 성형한다. 여기서, 압축속도와 압축비를 변화시켰을 때 발생되는 유리섬유의 배향에 관한 실험결과를 고찰한다.

• Journal of dental hygiene science
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• v.6 no.4
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• pp.231-235
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• 2006

This study evaluated the properties of polyvinylsiloxane impression materials: Strain-in-compression, Elastic recovery, Consistency, and Wettability. Four polyvinylsiloxane impression materials(Examixfine, GC, Japan; Aquasilultra, Dentsply, USA; Extrude, Kerr, USA; Perfect-F, Handae, Korea) were used in this study. The measured data were analyzed with SPSSWIN 12.0 program. The results were as follows : 1. The strain-in-compression values showed that Extrude had the lowest value, 4.86% and Examixfine had the highest value, 6.78%. Significant difference between Examixfine and Perfect-F was not found but the other groups had significant differences(p = 0.000). 2. In the elastic recovery test, Extrude had the highest, 99.83% and Perfect-F had the lowest, 96.54%. There is no significant difference between Examixfine and Aquasilultra. The other impression material groups showed significant differences(p = 0.000). 3. The measurement of consistency results that the diameter of Examixfine was the largest, 45.12mm and one of Perfect-F was the smallest, 40.28 mm. No differences were shown between Examixfine and Aquasilultra and between Extrude and Perfect-F(p = 0.001). 4. Aquasilultra had a better hydrophilicity($47.85^{\circ}$) than other materials. Perfect-F had a larger contact angle($94.89^{\circ}$) and was hydrophobic. There were significant differences between groups(p = 0.000). 5. As for correlation among the test types, contact angle correlated with strain-in-compression, elstic recovery and consistency. The strain-in-compression had correlation to contact angle and elastic recovery. The elastic recovery correlated with contact angle and strain-in-compression. And the consistency had correlation to contact angle.

• Steel and Composite Structures
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• v.27 no.6
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• pp.747-759
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• 2018

This study proposed a new type of concrete column that was confined with both steel angles and spiral hoops, named angle-steel and spiral confined concrete (ASCC) column. A total of 22 ASCC stub columns were tested under axial compression to investigate their behavior. For a comparison, three angle-steel reinforced concrete (ARC) stub columns were also tested. The test results indicated that ASCC column had a superior mechanical performance. The strength, ductility and energy absorption were considerably increased due to the improvement of confinement from spiral hoops. The confinement behavior and failure mechanism of ASCC column were investigated by the analysis of failure mode, load-deformation curve and section-strain distribution. Parametric studies were carried out to examine the influences of different parameters on the axial compression behavior of ASCC columns. A calculation approach was developed to predict the ultimate load carrying capacity of ASCC columns under axial compression. It was validated that the predicted results were in well agreement with the experimental results.

• Geomechanics and Engineering
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• v.12 no.3
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• pp.541-560
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• 2017

In this research, experimental and numerical simulations were adopted to investigate the effects of ligament angle on compressive strength and failure mode of rock-like material specimens containing two non-coplanar filled fissures under uniaxial compression. The experimental results show that with the increase of ligament angle, the compressive strength decreases to a nadir at the ligament angle of $60^{\circ}$, before increasing to the maximum at the ligament angle of $120^{\circ}$, while the elastic modulus is not obviously related to the ligament angle. The shear coalescence type easily occurred when ${\alpha}$ < ${\beta}$, although having the same degree difference between the angle of ligament and fissure. Numerical simulations using $PFC^{2D}$ were performed for flawed specimens under uniaxial compression, and the results are in good consistency with the experimental results. By analyzing the crack evolution process and parallel bond force field of rock-like material specimen containing two non-coplanar filled fissures, we can conclude that the coalescence and propagation of crack are mainly derived from parallel bond force, and the crack initiation and propagation also affect the distribution of parallel bond force. Finally, the displacement vectors in ligament region were used to identify the type of coalescence, and the results coincided with that obtained by analyzing parallel bond force field. These experimental and numerical results are expected to improve the understanding of the mechanism of flawed rock engineering structures.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.111-118
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• 2004

The work presented in this paper concerns the aerodynamic characteristics and compression wave generated in a tunnel when a high speed train enters it. A large number of solutions have been proposed to reduce the amplitude of the pressure gradient in tunnels and some of the most efficient solutions consist of (a) addition ofa blind hood, (b) addition of inclined part at the entrance, and (c) holes in the ceiling of the tunnel. These are numerically studied by using the three-dimensional unsteady compressible Euler equation solver with ALE, CFD code, based on FEM method. Computational results showed that the smaller inclined angle leads to the lower pressure gradient of compression wave front. This study indicated that the most efficient slant angle is in the range from $30^{\circ}$ to $50^{\circ}$. The maximum pressure gradient is reduced by $26.81\%$ for the inclined angle of $30^{\circ}$ as compared to vertical entry. Results also showed that maximum pressure gradient can be reduced by $15.94\%$ in blind hood entry as compared to $30^{\circ}$ inclined tunnel entry. Furthermore, the present analysis showed that inclined slant angle has little effect on aerodynamic drag. Comparison of the pressure gradient between the inclined tunnel hood and the vertical entry with air vent holes indicated that the optimum inclined tunnel hood is much more effective way in reducing pressure gradient and increasing the pressure rise time.

• Journal of the Korean Society of Clothing and Textiles
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• v.45 no.1
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• pp.106-122
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• 2021

This study confirmed the mechanical properties of an auxetic re-entrant pattern prepared using 3D printing technology and its composite fabric with neoprene for the production of functional auxetic patterns/textiles for safety shoes. Samples were prepared by the tilt angle of a re-entrant pattern of 0°, 30°, 45°, 60° and 90°, and then analyzed using Poisson's ratio, bending, compression, and tensile properties. A 3D printed auxetic re-entrant pattern (3DP-RE) and its composite fabric (3DP-RE/NP) showed a negative Poisson's ratio in all tilting angles that indicated auxetic properties. The results of the bending property shown that strength of 3DP-RE/NP was 1.5 times lower than NP, but the strain improved 2.0 times. It was confirmed that the deformation of 3DP-RE/NP is possible with a low load. Each sample type of compression behavior indicated similar regardless of the tilting angles; in addition, the compression toughness of 3DP-RE/NP increased 1.2 times compared with NP. In the case of tensile properties, 3DP-RE and 3DP-RE/NP were affected by the tilting angle, samples with 90° (the opposite of load direction) showed best tensile property and toughness. 3DP-RE/NP indicated improved bending, compression, and tensile properties.

• Structural Engineering and Mechanics
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• v.83 no.1
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• pp.19-29
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• 2022

The angle steel frame confined concrete columns (ASFCs) are an emerging form of hybrid columns, which comprise an inner angle steel frame and a concrete column. The inner angle steel frame can provide axial bearing capacity and well confining effect for composite columns. This paper presents the experimental and theoretical studies on the seismic behaviour of ASFCs. The experimental study of the 6 test specimens is presented, based on the previous study of the authors. The theoretical study includes two parts. One part establishes the section analysis model, and it uses to analyze section axial force-moment-curvature. Another part establishes the section moment-curvature hysteresis model. The test and analysis results show that the axial compression ratio and the assembling of steel slabs influence the local buckling of the angle steel. The three factors (axial compression ratio, content of angle steel and confining effect) have important effects on the seismic behaviour of ASFCs. And the theoretical model can provide reasonably accurate predictions and apply in section analysis of ASFCs.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.3
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• pp.947-954
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• 2014

In general, Fracture of the material is not occurring of the maximum normal stress or the maximum shear stress failure in the state. Maximum normal stress and maximum shear stress in the state of Critical coupling from being destroyed based on the Mohr-Coulomb theory. Couple of different mixtures, including permeable asphalt pavement, SMA and dense-graded asphalt mixture, were used for compression triaxial test at $45^{\circ}C$ and $60^{\circ}C$. Mohr-Coulomb theory to the analysis of compression triaxial test result of the internal friction angle $38.9^{\circ}{\sim}46.9^{\circ}$ measured somewhat irregularly, but in the case of cohesion, depending on whether the temperature and immersion of the specimen appeared differently. In addition, Indirect tensile test and compression triaxial test of the asphalt mixture to determine the correlation between compression triaxial test results assessed as cohesion and internal friction angle calculated using the theoretical Indirect tensile strength and measured indirectly tensile strength were analyzed. The Measured & Predicted IDT St values tended to be proportional.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.2
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• pp.50-59
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• 1997

When a front head of train enters a tunnel at a high speed, compression wave is generated at tunnel entrance due to the confinement effect and propagated along the tunnel with sound of speed. The propagated compression wave is reflected at tunnel exit due to abrupt pressure change at passage. The reflected wave is expansion pressure wave. And when the rear head of train goes through the tunnel entrance, another expansion pressure wave is generated and propagated along the tunnel. The pressure drop occurs seriously around train when the two expansion pressure waves come cross on train in the tunnel. In order to reduce the pressure drop, the compression wave front must be controlled because the intensity and magnitude of pressure drop is nearly proportional to that of compression wave at tunnel entrance. This study relates to reduction of the pressure wave gradient with respect to tunnel entrance shape change with various kind of angle and rounding. The results show characteristics of wave propagation in tunnel, usefulness of characteristic curve to estimate proper time domain size in numerical study and measuring time in actual experiment. Also rounding is contributed to improve pressure wave front even if its radius is very small at tunnel entrance. In order to improve of pressure wave front at tunnel entrance, proper angle is prefered to rounding with big radius and an angle of around 14$^{\circ}$ is recommended according to this simulations, And it is expected to reduce additional pressure drop in tunnel when the location and the size of the internal space for attendant equipment are considered in advance.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.872-877
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• 2003

The fixed-angle based modified compression field theory (MCFT) was developed to include the slip deformation across the crack, thereby allowing for the non-coincident directions of the principal strain and stress. To investigate the significance of crack modelling on the analysis, a series of tests on beams without transverse reinforcement was predicted by both rotating- and fixed-angle crack models within the frame of the MCFT. The results predicted by the fixed-angle MCFT were comparable to those by the rotating-angle MCFT when the initial crack angle of 45deg. and the related friction law are used.