• 한국가시화정보학회지
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• 제19권3호
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• pp.54-62
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• 2021

This study has investigated the 3-D deflection characteristics of a flexible plate levitated by non-contact grippers using SPIV method. The measuring instrument consisted of a flexible plate located under four non-contact grippers and two cameras at the bottom of a transparent acrylic plate. Measurements were made on two materials (PVC and PC) for the plate with 50×50 cm2 area and 1 mm thickness. The deflection characteristics and flatness vary depending on the plate material, the gripper position and the air flow supplied to the gripper. For the material of PVC, the overall defection is convex. As the gripper position goes outward from the plate center, the upmost bending point also moves to the outside of the plate with the flatness increasing. However, the air flow rate does not affect the deflection pattern except for the small increase of flatness. For the material of PC, the shape of deflection changes from convex to concave as the gripper position goes out. The flatness is the highest at the point of transition from convex to concave, but the air flowrate has little effect on the flatness.

• 한국안전학회지
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• 제6권3호
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• pp.21-26
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• 1991

In this study, a crack closure behavior of Al-alloy 5052-H38 was investigated. The fatigue test was performed by the four-point bending test under the contast amplitude load. Stress ratio R was changed from-1.0 to 0.5. To mcasure the fatigue crack opening point, the graph of load vs. subtracted displacement by computer program was obtained from the X - Y plotter. In order to gain the displacement data, a strain gage was attached at the back surface against the notched side. Uslng the conception of crack closure and influence of on crack growth rate a model for crack growth rate is developed for Al-alloy 5052-H38.

• Computers and Concrete
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• 제4권2호
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• pp.83-100
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• 2007

Applying a direct formulation for the enrichment of the displacement field an extended finite element (XFEM) scheme for modeling of cohesive crack growth is developed. Only elements cut by the crack is enriched and the scheme fits within the framework of standard FEM code. The scheme is implemented for the 3-node constant strain triangle (CST) and the 6-node linear strain triangle (LST). Modeling of standard concrete test cases such as fracture in the notched three point beam bending test (TPBT) and in the four point shear beam test (FPSB) illustrates the performance. The XFEM results show good agreement with results obtained by applying standard interface elements in FEM and with experimental results. In conjunction with criteria for crack growth local versus nonlocal computation of the crack growth direction is discussed.

• 산업기술연구
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• 제9권
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• pp.43-49
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• 1989

In this study, 3-point bending test for the mode I state and 4-point shear test for the mode II state were adopted to verify the crack initiation load level through comparing the test results of the acoustic emission and the ASTM testing criteria, using Jecheon granite, as the rock sample. The major result obtained in this study is that the crack initiation load levels obtained by using ASTM testing criteria and by measuring acoustic emissions showed analogous, roughly. However in case of demanding high safety, the crack initiation load level needs to be underestimated to the level that the crack begins to deform nonlinearly.

• The Journal of Advanced Prosthodontics
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• 제3권3호
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• pp.136-139
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• 2011

PURPOSE. A new light curing urethane dimethacrylate and a cold curing resin with simpler and faster laboratory procedures may have even improved flexural properties. This study investigated the 3-point flexural strengths and flexural moduli of two alternate base materials. MATERIALS AND METHODS. A cold curing resin (Weropress) and a light curing urethane dimethacrylate base material (Eclipse). Along with Eclipse and Weropress, a high impact resin (Lucitone199) and three conventional base materials (QC 20, Meliodent and Paladent 20) were tested. A 3-point bending test was used to determine the flexural strengths and flexural moduli. The mean displacement, maximum load, flexural modulus and flexural strength values and standard deviations for each group were analyzed by means of one-way analysis of variance (ANOVA) (with mean difference significant at the 0.05 level). Post hoc analyses (Scheffe test) were carried out to determine the differences between the groups at a confidence level of 95%. RESULTS. Flexural strength, displacement and force maximum load values of Eclipse were significantly different from other base materials. Displacement values of QC 20 were significantly different from Lucitone 199 and Weropress. CONCLUSION. The flexural properties and simpler processing technique of Eclipse system presents an advantageous alternative to conventional base resins and Weropress offers another simple laboratory technique.

• 한국세라믹학회지
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• 제51권5호
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• pp.459-465
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• 2014

In this study, Si-SiC composites were fabricated using a Si melt infiltration method using ${\beta}$-SiC/C composite powders synthesized by the carbothermal reduction of $SiO_2-C$ precursors made from a TEOS and a phenol resin. The purity of the synthesized SiC-C composite powders was higher than 99.9993 wt% and the average particle size varied from 4 to $6{\mu}m$ with increasing carbon contents of the $SiO_2-C$ precursors. It was found that the Si-SiC composites fabricated in this study consist of ${\beta}$-SiC and residual Si, without any trace of ${\alpha}$-SiC. The 3-point bending strengths of the fabricated Si-SiC composites were measured and found to be higher than 550 MPa, although the density of the fabricated Si-SiC composite was less than $2.9g/cm^3$. The bending strengths and the densities of the fabricated Si-SiC composites were found to decrease with increasing C/Si mole ratios in the SiC-C composite powders. The specific resistivities of the Si-SiC composites fabricated using the SiC-C composite powders were less than $0.018{\Omega}cm$. With increasing C content in the SiC-C composite powders used for the fabrication of Si-SiC composites, the specific resistivity of the Si-SiC composites was found to slightly increase from 0.0157 to $0.018{\Omega}cm$.

• 대한토목학회논문집
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• 제33권5호
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• pp.1935-1946
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• 2013

본 연구에서는 변단면 단일 현장타설말뚝의 거동 특성을 평가하고자 현장재하시험 사례를 분석하였으며, 또한 3차원 유한요소해석을 이용하여 말뚝 내부에서 발생하는 응력을 통해 심도별 휨응력을 산정하였다. 분석 결과, 단일 현장타설말뚝의 변단면 부근에서 휨응력이 집중되어 재료파괴가 발생하기 가장 쉬운 것을 알 수 있었다. 이를 토대로, 단일 현장타설말뚝의 기둥-말뚝 직경비와 수평 균열하중비 관계를 통해 최적의 기둥-말뚝 직경비를 제안하였다. 연구 결과, 최적의 기둥-말뚝 직경비는 기둥-말뚝 직경비와 수평 균열하중비 관계 곡선의 변곡점 부근에서 산정되었으며, 단일 현장타설말뚝 설계에 최적 변단면 특성을 고려한다면 개선된 설계가 이루어질 수 있을 것으로 판단되었다.

• 한국염색가공학회지
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• 제28권4호
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• pp.246-252
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• 2016

In comparison to metal alloys, braided composite features a high impact resistance and crash energy absorption potential, and also it still remained competitive stiffness and strength properties. Braiding angle is one of the most important parameters which affect the mechanical behaviors of braided composite. This paper presents transverse low velocity impact failure behavior analysis on the carbon 3D triaxial braided composite tube with the braiding angle of $20^{\circ}$, $50^{\circ}$ and $80^{\circ}$. The flexural behaviour of 3D triaxial braided composite tube under bending loads was studied by conducting quasistatic three point bending test. Also, the low velocity impact responses of the braided composite tubes were also tested to obtain load-displacement curves and energy absorption. Consequently, the increase of the braided angle, the peak load also increases owing to the bigger bending stiffness.

• 대한기계학회논문집A
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• 제39권10호
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• pp.963-970
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• 2015

다양한 분야에서 금속 재료의 우수한 기계적 특성을 위해 경량화는 필수적이다. 최근에는 보다 효율적인 차체 경량화와 함께 내충격성 강화를 위하여 금속 부품 대신에 섬유 금속 적층판을 이용하는 연구가 활발히 진행되고 있다. 경량화를 위해서 자동차 및 항공기에서 복합재료나 샌드위치 구조로 이루어진 섬유 금속 적층판이 유용하다. 하지만, 섬유 금속 적층판 형태에 따른 기계적 특성이 도출되지 않은 실정이다. 본 논문에서는 적층판 두께 조합에 따른 특성 비교를 위하여 두께를 인자로 하고, 섬유 금속 적층판의 완전 요인 배치법으로 실험을 계획한다. 또한 유한요소 해석을 사용하여 알루미늄 판과 섬유 금속 적층판을 탄성과 소성 해석을 한다. 이를 통해 적층판 두께 조합에 따른 섬유 금속 적층판 형태에 따른 기계적 특성을 분석하고, 굽힘 대변형 거동을 예측하는 유한요소 해석모델을 구축한다.

• 전자공학회논문지A
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• 제32A권8호
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• pp.153-165
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• 1995

The design procedure of a GaAs/AlGaAs semiconductor matrix optical switch is presented for a simplified tree architecture in the viewpoint of optical loss. A low loss, 0.537 dB/cm, pin type substrate is designed by considering the loss due to imputity doping at 1.3 $\mu$m wavelength. The operating voltage and the device length of a reversed ${\Delta}{\beta}$ electro-optic directional coupler(EODC) swith which is a cross-point device of the 4${\times}$4 matrix optical switch and the bending loss of rib waveguide are caculated as functions of waveguide parameters and bending parameters. There is an optimum bending radius for some waveguide parameters. It is recommened that higher optical confinement conditions such as wide waveguide width and higher rib-height should be chosen for structural parameters of a low loss and a process insensitive 4${\times}$4 matris optical switch. A 4${\times}$4 optical matrix switch which has a 3 dB loss and a 12 volt operating voltage is designed.