• 대한기계학회논문집A
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• 제20권8호
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• pp.2431-2435
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• 1996

In order to determine the effects of hydrostatic pressure on the mechanical behavior of graphite fiber reinforced composites, the modulus, fracture stress(maximum stress), and fracture strain of graphite/epoxy composites have been determined as a function of pressure. Composite specimens used in this study were 90-deg unidirectional and had a 60% fiber volume fraction. Compressive tests under five different pressure levels were conducted. The result showed the modulus measured from as initial slope of stress-strain curve increased bilinearly with pressure with a break at 200 MPa. It was also found that fracture stress and fracture strain increased in a linear fashion with pressure.

• 한국공작기계학회논문집
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• 제10권1호
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• pp.23-29
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• 2001

Cylindrical type of self-controlled restrictor are designed for hydrostatic bearing of grinding wheel spindle. Typical hydrostatic journal bearing with the designed restrictor is analytically model. According to the model, the affect of oper-ation parameters, such as, initial cross distance, supply pressure, diameter of two supply holes, pre-load of spring, and clearance between spindle and housing, on bearing stiffness are analyzed. From the results of the analysis, the optimum conditions of operation parameters that maximize the bearing stiffness are estimated.

• 소성∙가공
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• 제15권3호
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• pp.220-225
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• 2006

This paper investigates the characteristics of a hydro-mechanical punching process. The hydro-mechanical punching process is divided into two stages: the first stage is the mechanical half piercing in which an upper punch goes down before the initial crack is occurred; the second stage is the hydro punching in which a lower punch goes up until the final fracture is occurred. Ductile fracture criteria such as the Cockcroft, Brozzo and Oyane are adopted to predict the fracture of sheet material. The index values of ductile fracture criteria are calculated with a user material subroutine, VUMAT in the ABAQUS Explicit. The hydrostatic pressure retards the initiation of a crack in the upper region of the blank and induces another crack in the lower region of the blank during the punching process. The final fracture zone is placed at the middle surface of the blank to the thickness direction. The result demonstrates that the hydro-mechanical punching process makes a finer shearing surface than the conventional one as hydrostatic pressure increases.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.159-162
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• 2005

The milli-components for electronic and medical device etc. have been manufactured by conventional process. Forming and machining process for those milli-components need tremendous cost and time because products require higher dimensional accuracy than the conventional ones. For instance, conventional mechanical punching process has many drawbacks for applying to high accuracy products. The final radius of hole can be varied and burr which interrupting another procedure is generated. Hydro-mechanical punching process makes possible to reduce amount of burr and obtain the fine shearing surface using the operating fluid. Hydrostatic pressure retards occurrence of initial crack and induces to locate the fracture surface in the middle of sheet to thickness direction. In this paper, Hydro-mechanical punching process is analyzed using finite element method and the effect of hydrostatic pressure is evaluated during punching process. The prediction of fracture is performed adopting the various ductile fracture criteria such as Cockcroft, Brozzo and Oyane's criterion using a user subroutine in ABAQUS explicit.

• 한국식품과학회지
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• 제32권3호
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• pp.598-603
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• 2000

열처리에 의한 식품의 성분변화 손실을 줄이기 위한 비열처리 기술중 하나로 새롭게 주목받고 있는 초고압 처리를 적용하여 저염발효 새우젓의 저장성을 증진시키고자 하였다. 염농도 8%로 $20^{circ}C$에서 6주간 발효한 새우젓의 Vibrio 선택배지 검출균은 $1.6{\times}10^3\;CFU/g$, Staphylococcus 선택배지 검출균은 $9.3{\times}10^3\;CFU/g$이었고 18%의 새우젓에서의 Vibrio 선택배지 검출균은 $1.4{\times}10^4\;CFU/g$, Staphylococcus 선택배지 검출균은 $1.7{\times}10^\;CFU/g$이었다. 새우젓을 압력 $3,500{sim}6,500$기압, 시간 $5{\sim}40$분의 범위로 초고압 살균하였을 때 압력과 처리시간이 증가할수록 살균효과가 증가되었으며 사멸패턴은 1차반응으로 확인되었다. 압력을 6,500기압으로 고정하고 10분 동안 처리하였을 때 유해가능 세균은 본 연구방법의 검출한계인 $10^2\;CFU/g$수준에서는 경출되지 않았다. Vibrio선택배지 검출균의 $D_p$값은 염농도 8%보다 18%에서 더 높았으며 Staphylococcus 선택배지 검출균은 18%보다 8%에서 더 높은 값을 보였다. Vibrio 선택배지 검출균과 Staphylococcus 선택배지 검출균 모두 염농도 8%에서의 $Z_p$값이 염농도 18% 경우보다 높은 값을 보였다. 초고압 공정은 저염발효 새우젓의 살균에 응용될 수 있었으며 최적 고압살균조건은 6,500기압에서 10분간 처리하는 것이었다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1999년도 추계학술대회 논문집 - 한국공작기계학회
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• pp.425-431
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• 1999

Nowadays development of electric and optical devices needs precision more and more. This study focuses on hydrostatic journal bearing of grinding wheel spindle. It presents theoretical analysis about cylinder type self-controlled restrictor to control flux of oil flowing into pockets around the hydrostatic journal bearing. As a result of this analysis, optimal properties to maximize bearing stiffness such as initial cross distance, supply pressure, diameter of two supply holes, pre-load of spring and clearance between spindle and housing can be obtained. Therefore, by using them it is possible to estimate bearing stiffness and the performance of grinding wheel spindle can be improved.

• 한국항공우주학회지
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• 제37권2호
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• pp.147-155
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• 2009

외부 수압을 받는 필라멘트 와인딩 후판 복합재 원통의 좌굴 및 파손을 유한요소법과 시험으로 연구하였다. 자체 개발 프로그램인 ACOS와 상업용 프로그램인 MSC.NASTRAN(선형)과 MSC.MARC(비선형)를 이용한 유한요소해석을 수행하였다. 복합재 원통 시편은 T700 카본-에폭시로 필라멘르 와인딩 기법에 의해 $[\pm30/90]_{FW}$, $[\pm45/90]_{FW}$, $[\pm60]_{FW}$, $[\pm60/90]_{FW}$의 각도로 제작하여 수압시험을 수행하였다. 사용한 세 가지 프로그램 중 ACOS가 시험값과 1.7~14.3%의 차이를 보이며 좌굴 압력을 가장 잘 예측하였다. 모든 경우에 좌굴 후 지지하중이 초기 좌굴하중보다 커지지 못하고 최종파손으로 연결되었다.

• Journal of Ginseng Research
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• 제44권1호
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• pp.154-160
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• 2020

Background: Korean ginseng (Panax ginseng Meyer) powder is in rising demand because powder forms of foods are convenient to handle and are highly preservable. However, ginseng powder (GP) manufactured using the conventional process of air drying and dry milling suffers nutrient destruction and a lack of microbiological safety. The objective of this study was to prepare GP using a novel process comprised of UV-TiO₂ photocatalysis (UVTP) as a prewashing step, wet grinding, high hydrostatic pressure (HHP), and freeze-drying treatments. Methods: The effects of UVTP and HHP treatments on the microbial population, ginsenoside concentration, and physiological characteristics of GP were evaluated. Results: When UVTP for 10 min and HHP at 600 MPa for 5 min were combined, initial 4.95 log CFU/g-fw counts of total aerobes in fresh ginseng were reduced to lower than the detection limit. The levels of 7 major ginsenosides in UVTP-HHP-treated GP were significantly higher than in untreated control samples. Stronger inhibitory effects against inflammatory mediator production and antioxidant activity were observed in UVTP-HHP-treated GP than in untreated samples. There were also no significant differences in CIELAB color values of UVTP-HHP-treated GP compared with untreated control samples. Conclusion: Combined processing of UVTP and HHP increased ginsenoside levels and enhanced the microbiological safety and physiological activity of GP.

• 한국해양공학회지
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• 제26권2호
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• pp.79-84
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• 2012

This study aimed to analyze the nonlinear buckling of ring-stiffened circular cylinders under uniform external pressure, e.g. hydrostatic pressure, considering material nonlinearity and initial imperfection. In the present study, we analyzed the collapse pressure of pressure vessels using ANSYS Workbench, which is a framework of finite element methods. First, linear buckling analysis is performed to find collapse modes of the model. Second, scaling the first mode shape with small factor, geometric model is pre-deformed. And then, by analyzing the nonlinear buckling of the pre-deformed shape, the collapse pressure is estimated. To verify the validity of the analyses, we compared the results with Ross' experimental results. Finally, we applied it to ring-stiffened circular cylindrical shell of the pressure hull of a small submarine.

• 한국지반공학회논문집
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• 제23권10호
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• pp.73-84
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• 2007

원추 후면에서 간극수압이 측정되는 표준 피에조콘의 경우, 일반적인 소산곡선은 간극수압이 초기값에서부터 단조적으로 감소하는 경향을 보인다. 그러나, 간극수압이 일시적으로 증가한 후에 감소하는 지연소산 거동이 과압밀비 4 이하의 약간 과압밀된 점성토 지반에서 확인되었다. 이와 같은 비정규적인 소산 거동은 주로 매우 과압밀된 지반에서 발생하는 것으로 보고되었으며, 기존의 연구도 이러한 경우로 한정되어 진행되었다. 본 연구에서는 약간 과압밀된 점성토 지반에서 발생하는 지연소산의 메커니즘을 규명하였다. 피에조콘 시험으로부터 산정된 지반의 특성과 지연소산의 상관성을 분석하였으며, 콘 관입 이후의 소산거동에 대하여 유한차분해석을 수행하였다. 연구 결과, 약간 과압밀된 점성토에서는 원추 선단에서 발생하는 큰 과잉간극수압이 원추 후면 필터로 상향 전파되어 지연소산이 유발되고, 과압밀비(OCR) 및 정수일$(u_0)$과 관련된 원추 선단과 원추 후면의 초기 과잉간극수압비$({\Delta}u_{1i}/{\Delta}u_{2i})$가 지연소산에 영향을 미치는 것이 확인되었다.