• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1997년도 Proceedings of the 12th KACG Technical Meeting and the 4th Korea-Japan EMGS (Electronic Materials Growth Symposium)
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• pp.13-17
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• 1997

The densification of $Al_2$O$_3$/15v/o ZrO$_2$ (Zirconia Toughened Alumina: ZTA) to the 99% of theoretical density was attempted by controlling the processing parameters affecting the each processing step i.e., milling, spray-drying, forming and pressureless sintering. The ZTA processed under the identical conditions showed a large variation in the green and sintered densities, and the mechanical properties. The deviation of 4-point bending strength was more than 100MPa for the ZTA with ~99% of theoretical density. Moreover, the relative green and sintered densities were deviated greatly from the average value. This low reproducibility could be caused by the variation of spray-dried granule properties. Thus, the effect of yield strength and morphology of spray-dried ZTA granule on the green and sintered densities and the mechanical properties needs to be studied in detail. The objective of this work is to fine out the optimum condition of compaction pressure and compaction method depending on the properties of spray-dried granules.

• Computers and Concrete
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• 제19권6호
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• pp.631-639
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• 2017

This study experimentally investigated the flexural capacity of a concrete beam reinforced with a newly developed GFRP bar that overcomes the lower modulus of elasticity and bond strength compared to a steel bar. The GFRP bar was fabricated by thermosetting a braided pultrusion process to form the outer fiber ribs. The mechanical properties of the modulus of elasticity and bond strength were enhanced compared with those of commercial GFRP bars. In the four-point bending test results, all specimens failed according to the intended failure mode due to flexural design in compliance with ACI 440.1R-15. The effects of the reinforcement ratio and concrete compressive strength were investigated. Equations from the code were used to predict the deflection, and they overestimated the deflection compared with the experimental results. A modified model using two coefficients was developed to provide much better predictive ability, even when the effective moment of inertia was less than the theoretical $I_{cr}$. The deformability of the test beams satisfied the specified value of 4.0 in compliance with CSA S6-10. A modified effective moment of inertia with two correction factors was proposed and it could provide much better predictability in prediction even at the effective moment of inertia less than that of theoretical cracked moment of inertia.

• 한국세라믹학회지
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• 제55권6호
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• pp.597-607
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• 2018

In this study, a wet chemical method was used to synthesize nanostructured hydroxyapatite for biomedical applications. Diammonium hydrogen phosphate and calcium nitrate 4-hydrate were used as starting materials with a sodium hydroxide solution as an agent for pH adjustment. Scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, differential thermal analysis, thermal gravimetric analysis, atomic absorption spectroscopy, and ethylenediaminetetraacetic acid (EDTA) titration analysis were used to characterize the synthesized powders. Having been uniaxially pressed, the powders formed a disk-like shape. The sinterability and electrical properties of the samples were examined, and the three-point bending test allowed for the measurement of their mechanical properties. Sedimentation analysis was used to analyze the slurry ability of hydroxyapatite. As in-vitro biological properties of the samples, biocompatibility and cytotoxicity were assessed using osteoblast-like cells and the L929 cell line, respectively. Solubility was assessed by employing a simulated body fluid.

• Journal of Advanced Marine Engineering and Technology
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• 제33권2호
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• pp.330-335
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• 2009

A fiber-optic liquid level sensor based on bending cantilever beam has been proposed. A fiber Bragg grating(FBG) embedded in the cantilever beam is used to sensing elements. The basic concept is elongation and constriction of the FBG corresponding to the liquid level variation. The best FBG position on the cantilever for obtaining the high sensitivity was 4 cm from the fixing point. When the liquid level moves up and down vertically, the Bragg wavelength is linearly shifted. But, the wavelength sensitivity of the FBG installed on the upper side of cantilever was four times better than that of the FBG equipped in the lateral side due to the difference of unit strain applied to the FBG. Intensity demodulation using the low-cost edge filter is used to interrogate the Bragg wavelength through converting the wavelength signals into the optical intensity ones. Experiment results show that the electrical output is exponentially proportional to the liquid level. But, it should be overcome for applying to the ships.

• 수산해양기술연구
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• 제26권2호
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• pp.204-212
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• 1990

The SMC composite, now being considered in certain structural applications, is anticipated to experience repeated loading during service. Thus, understanding of the fatigue behavior is essential in proper use of the composite material. In this paper, using the SMC composite composed of E-glass chopped strand and unsaturated polyester resin three point bending fatigue tests are carried out to investigate the fatigue crack propagating behavior under various cyclic stresses and fatigue damage of various microcrack forms. The following results are obtained from this study; 1) Most of the total fatigue life of the SMC composite is consumed at the initial extension or the growth of the macroscopic crack. 2) A Paris' type power-law relationship between the crack propagation rate and stress intensity factor range is obtained, and the value of material constant m is much higher (m=9~11)than that of other metals. 3) In case of high cyclic stress the fatigue damage show high microcrack density and short crack length, but in case of low cyclic stress does it vice versa. 4) Fatigue damage is characterized by microcrack density, crack length and distribution of crack orientation.

• Composites Research
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• 제16권4호
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• pp.59-65
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• 2003

샌드위치 구조물의 응용된 형태인 스마트 스킨 구조물을 ABAQUS로 유탄요소 해석하였다. 심재로 쓰이는 하니컴은 일반적으로 두께 방향 강성 및 전단 강성만 제작회사에 의하여 제공된다. 이를 바탕으로 하니컴 재료의 물성을 추정하여 다른 방향의 제공되지 않는 물성을 계산하였고, 이를 유탄요소 해석시 물성 자료로 적용하였다. 또한, 스마트 스킨 구조물의 좌굴 및 3점 굽힘 거동을 유한요소 해석하였으며, 기존의 실험결과 및 이론값과 비교 분석하였다. 비교적 결과가 잘 일치하였다. 본 연구를 통하여서 하니컴의 물성을 상용 패키지에 적용하는 방법 및 타당한 근거를 제시하였고, 이 결과를 바탕으로 스마트 스킨 구조물을 상용패키지로 유한요소 해석시 지침을 제시할 수 있다

• 동력기계공학회지
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• 제13권4호
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• pp.43-48
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• 2009

The purpose of this study is to show how to eliminate the noises and to obtain the data related with the relationship between AE signal characteristics and mechanical behaviors for the pressure vessel steel. Various kinds of noises are introduced into the AE data in the course of experiments. Accordingly, real AE data have to be obtained after tests. AE test was carried out under four point bending load. Among AE signals, counts and signal strength are used to find out the differences of AE characteristics between the basemetal and weldment. After tests, this paper shows the procedures of filtering the noises against basemetal of the pressure vessel steel to obtain the real data around crack tip. Relationships between plastic zone size and cumulative AE counts are shown also. AE signals were absent within an elastic region, regardless of the specimens. Most of AE signals are produced in the process of plastic deformation. The deformation and fracture modes of basemetal and weldment are quiet different.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.742-745
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• 2004

The FRP-concrete composite deck system has advantages of corrosion free and easy construction. The system is, however, comprised of two brittle materials, so that it suffers from inherent disadvantage of lack of ductility. In this study, some conceptual design is presented for preventing the brittle failure of FRP-concrete composite deck at ultimate load level. 4-point bending tests are performed for FRP-concrete composite beams using FRC(Fiber Reinforced Concrete). The specimens use the box-shape FRP member in the lower portion. Four types of concrete with different compressive strengths and ductilities including normal mortar and 3 FRCs are placed in the upper portion. Typical failure mode in the test is identified; Concrete compressive failure occurs first at the maximum moment region, and the interfacial debonding between FRP and concrete member proceeds. Finally, the tensile rupture of FRP member occurs. The specimen using FRC with the high compressive ductility of concrete fails with less brittle manner than other specimens. The reason is that the ductility from the concrete in compression prevents the sudden loss of load-carrying capacity after compressive concrete failure.

• 한국안전학회지
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• 제25권3호
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• pp.71-77
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• 2010

This paper presents the results of a study on flexural capacity of large size RC slabs strengthened with carbon fiber reinforced polymer(CFRP) plates. A total of 5 specimens of 6.0m length were tested in four point bending after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with two prestress levels, 0.4% and 0.6% of CFRP plate strain. Test variables included the type of strengthening, prestressing level, and the effects according to each test variables are analysed. The experimental results show that proposed methods can increase significantly the flexural capacity such as strength, stiffness of the beam and the increase ranged between 36.2% and 63.2% of the load-carrying capacity of the control beams. The non-prestressed specimen failed by separation of the plate from the beam due to premature debonding while most of the prestressed specimens failed by CFRP plate fracture. And the cracking loads and maximum loads were increased proportionally to the prestress level.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.54-58
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• 2008

The structural intensities have been applied to understand a source point and the path of vibrational energy flows in interested structures by many researchers. In this paper, a feasibility study was carried out to investigate the characteristics of a damaged beam with a inflicted open crack using the structural intensities. The damaged beam was taken as a continuous system with equivalent bending stiffness and the flexural vibrations were only considered in numerical simulation and experiments. A four(4)-transducer array was used to measure the flexural vibrations of the beam and the structural intensities were estimated by means of cross spectral density method. As a result, the magnitude changes of the structural intensities could be observed in the vicinity of the damage location and a damage index was newly proposed to identify the damage zone. It has been confirmed that the measurement of the structural intensities was simple and effective method to find out the damage zone.