• Journal of Information Display
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• v.4 no.1
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• pp.1-8
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• 2003

Recent progress in both low pretilt and high pretilt defect free C1 surface stabilized ferroelectric liquid crystal (SSFLC) devices is reviewed. First, by numerical calculation to investigate the balance between surface azimuthal anchoring energy and bulk elastic energy within the confined chevron layer geometry of C1 and C2, it is possible to achieve a zigzag free C1 state by low azimuthal anchoring alignment with a low pretilt angle. The critical azimuthal anchoring coefficient for defect free C1 state is calculated. Its relationship with elastic constant, chevron angle as well as surface topography effect are also discussed. Second, using $5^{\circ}$ oblique SiO deposition alignment method a defect free, large memory angle, high contrast ratio and bistable C1 SSFLC display, which has potential for electronic paper applications has also been developed. The electrooptical properties and bistability of this device have been investigated. Various aspects of defect control are also discussed.

• Transactions of Materials Processing
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• v.33 no.1
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• pp.43-49
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• 2024

A high strength steel sheet (HSSS) has widely used to improve the specific rigidity of parts and the safety of the passenger in automotive industries. However, the HSSS is difficult to manufacture precise parts through a forming process due to the reduced elongation and the increased elastic recovery. The goal of the paper is to investigate the improved design of bending dies for DP590 HSSS. The over forming type bending dies with cam systems added to the side of the formed part is proposed to improve the quality of the part. The effects of the die design and the forming parameter on formability and elastic recovery characteristics is examined using finite element analyses (FEAs). From the results of FEAs, proper die design and forming parameters are predicted.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.23-29
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• 2023

The goal of this study is to evaluate the bursting characteristics and fire resistance performance of mixed cement concrete containing fibers at very high temperatures. For this purpose, FA-based, Slag-based, and each mix according to the amount of fiber mixed were heated to room temperature, 150℃, 300℃, 600℃, and 900℃, and then the burst shape, compressive strength, and elastic modulus were measured and evaluated. As a result of the experiment, it was found that relatively more surface damage occurred in FA-based specimens when heated at ultra-high temperatures than in slag-based specimens, and there was a difference between the mix without fibers and the mix with fibers when heated at ultra-high temperatures, that is, at 900℃. In the mix without fibers, a decrease in strength of more than 5% occurred. In addition, the elastic modulus also showed the same phenomenon as the compressive strength, and in particular, the decrease in elastic modulus was found to be greater than the amount of decrease in compressive strength. Meanwhile, estimation equations for compressive strength and elastic modulus according to heating temperature were statistically proposed.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.613-620
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• 2013

Concrete has been recognized as a material which is resistant to high temperatures, but chemicophysical property of concrete is changed by the high temperature. So, mechanical properties of concrete may be reduced. Because of this, standards and researches on the degradation of the mechanical properties of concrete at high temperatures have been presented. However, research data about the state that considering the loading condition and high-strength concrete is not much. Therefore, this study evaluated the high-temperature properties of high-strength concrete by loading condition and elevated temperature. The stress-strain, strain at peak stress, compressive strength, elastic modulus, thermal strain and the transient creep are evaluated under the non-loading and $0.25f_{cu}$ loading conditions on high strength concrete of W/B 12.5%, 14.5% and 20%. Result of the experiment, decrease in compressive strength due to high temperature becomes larger as the compressive strength increases, and residual rate of elastic modulus and compressive strength is high by the shrinkage caused by loading and thermal expansion due to high temperature are offset from each other, at a temperature above $500^{\circ}C$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.6
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• pp.589-593
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• 2015

The demand of high cycle fatigue behavior on plate material is increasing because of its various applications. However, the high-cycle fatigue life data of the plate material is very rare compared to the rod material. Thus, in this study, a plate specimen is designed for the ultrasonic fatigue test because it is time efficient as compared to the conventional fatigue test. To apply the ultrasonic fatigue test, the specimen design is required to resonate at 20 kHz. Therefore, the dynamic elastic modulus was determined by measuring the resonance frequency with a piezoelectric element and laser doppler vibrometer (LDV). As a result, the plate specimen is designed and demonstrated using the ultrasonic fatigue testing machine. The ultrasonic fatigue test results were compared with the hydraulic fatigue test results.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.127-128
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• 2014

The aim of this research is selecting an economical aggregate type for ultra-high strength concrete with 80 to 120 MPa of compressive strength. As the tests, the effect of water-to-binder ratios and types of aggregate on autogenous shrinkage of ultra-high strength concrete were evaluated. as the results of a series of tests performed, the slump flow was satisfied the target range of 600 ± 100 mm, and the concrete mixture with RLA showed higher elastic modulus than the other cases. For the autogenous shrinkage preventing performance, in the case of water-to-binder ratio of 15, and 20 %, the mixture with BA showed slightly improved autogenous shrinkage reducing effect than the mixture with RLA while the mixture with RLA showed better performance at 25 % of water-to-binder ratio. Therefore, based on the tests results of slump flow, elastic modulus, and autogenous shrinkage, the RLA is considered as a better aggregate type for this purpose.

• Fashion & Textile Research Journal
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• v.2 no.3
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• pp.227-233
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• 2000

The purpose of this study was to develop the High Functional Covering machine and the Compound Twister to produce the high value added textile goods and to meet the consumer's needs. For the study, 8 yarns and 12 fabrics were made with two developed machines and the tensile characteristics of the samples were tested and analysed. The result indicated that the sample fabrics kept their elongation regardless of buffering process. Elongation of the sample yarns was higher than those of yarns made with a traditional covering method. Elastic recovery of the sample fabrics was more effected by the recovery rate than by the number of extension and the characteristics of the sample yarns and fabrics were comparable to the yarns and fabrics made with a traditional covering method in terms of the position of Spandex yarns in their yarn structure and buffering effect.

• Structural Engineering and Mechanics
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• v.40 no.6
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• pp.847-866
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• 2011

The objective of this study was to experimentally investigate the bond-related tension stiffening behavior of flexural reinforced concrete (RC) beams made with lightweight aggregate concrete (LWAC) under various high-cycle fatigue loading conditions. Based on strain measurements of tensile steel in the RC beams, fatigue-induced degradation of tension stiffening effects was evaluated and was, compared to reinforced normal weight concrete (NWC) beams with equal concrete compressive strengths (40 MPa). According to applied load-mean steel strain relationships, the mean steel strain that developed under loading cycles was divided into elastic and plastic strain components. The experimental results showed that, in the high-cycle fatigue regime, the tension stiffening behavior of LWAC beams was different from that of NWC beams; LWAC beams had a lesser reduction in tension stiffening due to a better bond between steel and concrete. This was reflected in the stability of the elastic mean steel strains and in the higher degree of local plasticity that developed at the primary flexural cracks.

• Journal of the Society of Disaster Information
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• v.16 no.4
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• pp.806-812
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• 2020

Purpose: This is aimed to evaluate the seismic fragility of curved bridge structure with I-shape girder subjected to 12 high frequency ground motions based on Gyeongju earthquake. Method: The linear elastic finite element model of curved bridge with I-Shape cross section was constructed and them linear elastic time history analyses were performed using the 12 artificial ground motions. Result: It was found that displacement response(LS1, LS2) was failed after PGA 0.1g and the stress response also showed failure after PGA 0.2g. Conclusion: The curved bridge with I-shape girder was sensitive to high frequency earthquakes.

• Tribology and Lubricants
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• v.39 no.1
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• pp.13-20
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• 2023

Large drill bits may face high hardness ore and high working pressure when working. To optimize the use effect of large drill bits and prolong the use time, it is necessary to add a layer of pressure-resistant, wear-resistant, and low-friction coating on the surface of the drill bit. In this study, CoCrNiAlTi high-entropy alloy coatings and CoCrNiAlTi (70 wt%)-TiC (30 wt%) composite coatings are successfully prepared on Q235 steel by plasma spraying. The CoCrNiAlTi (70 wt%)-TiC (30 wt%) coating consists of FCC solid solution and a small amount of TiC phase. The effect of TiC on the composition phase, microhardness, and elastic modulus of HEA coating is studied by X-ray diffractometer (XRD) and microhardness tester. The effect of TiC on the friction and wear properties of HEA coatings is investigated using a wear tester. By improving the process parameters, the metallurgical bonding between the coating and the substrate is well combined, and a coating without pores and cracks is obtained. The experimental results confirm that the microhardness, elastic modulus, and wear resistance of CoCrNiAlTi-TiC composite coating are better, and the friction coefficient is lower.