• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.6
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• pp.193-198
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• 2021

In this study, the rheological characteristics and of 3D printing composite materials and the compressive strength characteristics according to the lamination patterns were evaluated. As a result of rheology test, rapid material change was observed after 60 minutes of extrusion, yielding stress 1.4 times higher than immediately after mixing, and plastic viscosity was 14.94-25.62% lower. The compressive strength of the specimens manufactured in the mold and the laminated specimens were compared, and the lamination pattern of the laminated specimens were 0°, 45°, and 90° as variables. The compressive strength of the mold casting specimen and the laminated specimen from 1 to 28 days of age showed similar performance regardless of the lamination pattern. In particular, at the age of 28 days, the modulus of elasticity, maximum compressive strength, and strain at maximum stress of all specimens were almost the same. In order to analyze the interface of the laminated specimens, X-ray CT analysis of the specimen whose compressive strength were measured was performed. Through CT analysis, it was confirmed that cracks did not occur at the lamination interface, which can be judged that the interface in the laminated specimen behaved in an integrated manner.

• Clean Technology
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• v.16 no.2
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• pp.124-131
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• 2010

Effects of $Ca(OH)_2$ concentration (0.16~0.64 wt%), surfactant concentration (2~16 wt%), total volumetric flow rate (3~6 L/min) and $CO_2$ volume fraction $(0.3{\sim}0.6)$ on morphology, crystal structure, mean particle diameter, aggregation and specific surface area of the precipitated $CaCO_3$ were investigated in the slurry bubble column reactor. Experiments were carried out in acrylic reactor ($0.11\;m-ID{\times}1.0\;m-high$) with a internal tube ($0.04\;m-ID{\times}1.0\;m-high$h). The reaction time of $CaCO_3$ synthesis decreased with adding Dispex N40 of the anionic surfactant. The reaction rate of $Ca(OH)_2$ increased with increasing the volumetric flow rate of $CO_2$. From SEM images, the single crystal of $CaCO_3$ increased with increasing the reaction rate in the saturated concentration of $Ca(OH)_2$ (0.16 wt %) and the concentration of Dispex N40 (2 wt%). The mean particle size of $CaCO_3$ varied with adding Dispex N40. In addition, the specific surface area of $CaCO_3$ increased with adding of surfactant (2 wt%) from $35m^2/g$ to $44m^2/g$ at the volumetric flow rate of $CO_2$ (0.9 L/min) and the concentration of $Ca(OH)_2$(0.64 wt %).

• Applied Chemistry for Engineering
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• v.34 no.2
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• pp.137-143
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• 2023

In this study, natural surfactants were extracted from Medicago sativa L. The O/W emulsification processes with the extracted natural surfactants were optimized using central composite design model-response surface methodology (CCD-RSM) and a 95% confidence interval was used to confirm the reasonableness of the optimization. Herein, independent parameters were the ratio of saponins to total surfactant (P), amount of surfactant (W), and emulsification speed (R), whereas the reaction parameters were the emulsion stability index (ESI), mean droplet size (MDS), and viscosity (V). Using the multiple reaction, the optimal conditions for the ratio of saponins to total surfactant, amount of surfactant, and emulsification speed for O/W emulsification were 49.5%, 9.1 wt%, and 6559.5 rpm, respectively. Under these optimal conditions, the expected values of ESI, MDS, and V as the reaction parameters were 89.9%, 1058.4 nm, and 1522.5 cP, respectively. The values of ESI, MDS, and V from these expected values were 88.7%, 1026.4 nm, and 1486.5 cP, respectively, and the average experimental error for validating the accuracy was about 2.3 (± 0.4)%. Therefore, it was possible to design an optimization process for evaluating the O/W emulsion process with Medicago sativa L. using CCD-RSM.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.2
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• pp.71-78
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• 2018

This paper presents the assembling of multiple patches based on the single patch isogeometric formulation for the shear deformable shell element given in the previous study. The geometrically exact shell formulation has been accomplished with the shell theory based formulation and the generalized curvilinear coordinate system directly derived from the given NURBS geometry. For the knot elements matching across adjacent surfaces, the zero-th and first parametric continuity conditions are considered and the corresponding coupling constraints are implemented by a master-slave formulation between adjacent patches. The constraints are then enforced by a substitution method for condensation of the slave variables, thereby reducing the model size. Through numerical investigations, the important features of the first parametric continuity condition are confirmed. The performance of the multi-patch shell models is also examined comparing the rate of convergence of response coefficients for the zero and first order continuity conditions and continuity in coupling boundary between two patches is confirmed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.5
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• pp.603-608
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• 2010

In this study, one type of circular shaped composite tube was used, combined with reinforcing foam and without foam. Furthermore, CFRP(Carbon Fiber Reinforced Plastic) circular member manufactured from CFRP prepreg sheet for lightweight design. CFRP is an anisotropic material which is the most widely adapted lightweight structural member. The crashworthy behavior of circular composite material tubes subjected to static axial compression under same conditions is reported in this paper. Test was executed in order to compare the results to the energy absorption and collapse shape. The collapse mode during the failure process were observed and analyzed. The behavior of polymeric foams to the tubes crashworthiness were also investigated. According to the experimental results, specimens filled with foam are higher total energy absorption than the other specimens not filled with the foam.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.241.2-241.2
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• 2011

다공 소재는 큰 비표면적과 규칙적으로 정렬된 구조의 특성으로 인해 자성메모리 소자용 재료, 나노 와이어 제작용 템플릿, 마이크로 반응기, 메타물질용 소재 등으로 각광을 받고 있다. 자기조립 수직배열 다공구조 재료를 제작하는 방법으로 흔히 알루미늄의 양극산화 방법과 이원공정계의 상분리 방법이 등이 있다. 본 연구에서는 상변태를 비롯한 패턴형성과 계면 운동을 가장 정확하게 다루는 이론적 모델로 알려진 상장모델(Phase Field model)을 이용하여 이원공정계의 박막성장과정 동안의 자발적 상분리에 의한 수직배열 자기조립 다공구조 형성을 시뮬레이션 한다. 상장모델을 기초로 하여 상분리 메커니즘에 의해 발현된 미세조직을 해석하고 다양한 공정변수가 미세조직 발현에 미치는 영향에 대해 연구한다. 또한 상장모델을 통해 얻은 결과는 기존에 발표된 연구들의 결과와 비교를 통해 유효성을 입증한다.

• Korean Journal of Materials Research
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• v.6 no.9
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• pp.963-971
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• 1996

세라믹 강화 복합 재료의 모재로서 사용되는 무정형 PEEK가 보여주는 self-bonding 현상의 주 기구인 PEEK체인들의 확산(interdiffusion)과 뒤엉킴(entanglement)이 일어나기 위하여 PEEK의 접합 면에서 반드시 선행되어 일어나야 하는 젖음성의 정도에 미치는 접합 공정 변수의 영향을 C-mode acoustic microscopy를 이용하여 고찰하였다. 또한 self-bonding 된 PEEK시편들의 전단 변형시 전단 하중의 증가에 따라 일어나는 접합 면에서의 debonding 정도를 측정함으로써 접합 면에서 일어나는 파괴 거동을 관찰하였다. 각각의 접합 조건에서의 젖음성의 정도는 시간과 압력의 증가에 따라 다소 증가함을 보여 주었으나, 접합 온도와는 거의 무관함을 보여 주었다. 또한 전단 파괴 시험시 각각의 접합 조건 하에서 개발된 self-bonding강도의 80%-90%이상의 전단 하중이 가해진 후부터 debonding이 시작되어, 이 후 하중이 증가함에 따라 급속도로 진행되어 파괴가 일어남을 알 수 있었다.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.83-91
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• 1998

Cracking problems which high temperature plant components suffer during long-term service, occur very often at welded locations. The crack occurs due to accumulated creep damage near fusion line or at heat affected zone (HAZ). However, most of the studies on creep crack growth behavior have been performed with matrix metal not wit welded metal due to the difficulty of interpreting the test results. In this study, creep crack growth rates were measured with C(T) specimens whose cracks were formed along the fusion line or HAZ. The measured crack growth rates were characterized by {TEX}$C_{t}${/TEX}-parameter derived for elastic-primary-secondary creeping material. Since contribution of primary creep was significant for the tested 1Cr-0.5Mo steel, its effect was carefully studied. Effects of crack tip plasticity and material aging were also discussed.

• Korean Journal of Materials Research
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• v.8 no.5
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• pp.429-435
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• 1998

무정형 PEEK 필름의 self-bonding 공정 시에 일어나는 결정화 현상이 접합 면에서 개발되어지는 self-bonding 강도에 미치는 영향을 주사전자현미경(SEM)을 이용하여 고찰하였다. 무정형 PEEK 필름의 결정화 현상은 접합 시의 공정변수에 따라 변화하며, self-bonding 공정 동안 접합 면을 가로질러 PEEK의 결정들이 성장함에 따라 접합이 일어남을 알 수 있었다. 접합온도가 높을수록 접합 면을 가로지르는 결정들의 성장 정도가 낮은 온도에서 접합시켰을 때의 경우보다 훨씬 커서 결과적으로 높은 self-bonding 강도를 보였다. 각각의 시편들을 전단 파괴시킨 후 행한 파단면 관찰에서는 self-bonding 강도가 점차 높아짐에 따라 더욱 조밀한 물결무늬 파면과 dimple 형태와 유사한 파면 형상들이 관찰되는 것으로 보아 접합공정 시 접합 면을 가로지르는 PEEK 결정들의 성장 정도가 self-bonding 강도에 커다란 영향을 미친다고 판단되었다.

• Journal of the Korea Society for Simulation
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• v.14 no.2
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• pp.45-55
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• 2005

There are electric double layer capacitance, polarization resistance and solution resistance in the interface between electrode and solution. Electrode process could be evaluated by the electrical impedance analysis. The necessities of the electrochemical cell analysis with high speed impedance analyzer are followings: minimization of the effects of electric stimulation on electrochemical cell and the concentration of reactive materials, and optimization of impedance signal resolution. This paper represents the design criteria for the selection and stimulation to develop fast impedance analyzer prototype for a electrochemical cell. It was suggested that the design of 470k sample/s sampling rate, 13 bit ABC resolution, and 140ms recording time is required for high speed impedance analysis system in frequency range between dc and 10kHz.