• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.503-506
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• 2008

본 연구에서는 하이드로포밍 공정을 적용한 엔진크레들 제품에 대해 최종 제품의 강도를 평가하고자 하였다. 먼저 적용 판재인 370과 440 소재에 대해 인장시험을 수행하여 소재의 경도와 강도의 상관관계를 분석하여 경도와 강도의 변환식을 도출하였다. 그런 다음 예비굽힘, 예비성형, 최종성형된 제품의 각 공정에 따른 유효변형률을 측정하고 같은 위치에서의 경도를 측정하였다. 측정된 경도는 앞서 도출한 경도와 강도의 변환식에 대입하여 각 공정을 마친 제품의 강도를 예측하고 결국 하이드로포밍된 엔진 크레들 제품의 유효변형률에 따른 강도를 예측식을 실험으로 도출하였다. 그 결과 예비굽힘, 예비성형, 최종성형을 마친 엔진 크레들 제품에 대해 유효변형률이 $24{\sim}72%$로 변하였고 이때 HF370의 경우에는 유동응력값이 $375{\sim}500MPa$로 증가하여 원소재에 비해 성형 후 $25{\sim}66%$의 강도증가량을 보였고, HF440의 경우에는 $470{\sim}565MPa$로 증가하여, 원소재에 비해 $17{\sim}41%$로 강도가 증가하는 것으로 나타났다. 그리고 이와 같은 변화값을 이용하여 유효변형률과 강도의 상관관계를 도출하였다.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.5
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• pp.566-573
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• 2015

The most important factor for the penetration performance of shaped charge is the liner design. By designing the liner to have properties of both high jet tip velocity and long jet break-up time, the better penetration performance could be acquired. Usually it is very difficult to satisfy above two conditions simultaneously. In this study, the liner with the shape of ogive was developed to have relatively larger jet mass compared to the conventional trumpet liner. The designed shaped charge showed jet properties with high jet tip velocity and long jet break-up time by using ogive liner and wave shaper. A commercially available hydro-dynamic code AUTODYN-2D was used for numerical analysis of jet formation. The flash X-ray test and the static penetration test were conducted to verify the results of numerical analysis.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.230-233
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• 2006

In this study, the effects of residual stress induced by plastic injection molding process on the tensile behavior of plastic tensile test specimen were investigated. To manufacture plastic tensile test specimens, an injection mold based on the international standard system was designed and made. Cavity pressure and temperature sensors were installed inside of the presented mold to monitor pressure and temperature values during the cycle of injection molding. Injection molding simulation was performed with the same condition of experiment and linear structural tensile analysis was also performed with the initial condition of the residual stress. It was shown that the residual stress induced by injection molding has an effect on the experiment of tensile test and linear structural tensile simulation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.224-230
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• 1998

Non-heat-treated type material has been investigated for formability compared to heat-treated material. It is very important in automation of metal forming, since it has difficulties of controlling heat treating system by the computer and has bottle neck problem related with heat treatment. In this paper, we have concerned about mechanical properties of non-heat-treated material after the forging. To compare the characteristics between heat-treated material and non-heat-treated material, tensile, compression and fatigue test has been performed. Considering results of mechanical properites of non-heat-treated material, it can replace heat-treated material. Therefore non-heat-treated material may be applied to cold forging.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.251-252
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• 2006

Tensile and anisotropy test were performed to evaluate the mechanical properties of coated and uncoated steel. These results were used to predict the deference of formability between two sheets. Cup-drawing test was performed to verify formability of two sheets. Also, Cup-drawing test could predict the coefficient of friction and the forming limit. Finite Element Method of cup-drawing was performed to assess the deference between two sheets considering frictional characteristics. This result was compared with the former results.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1993.10a
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• pp.27-33
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• 1993

천마 연소관 및 Bracket는 고강도 특수강의 일종인 Maraging steel C-250 Grade로서 유동성형공정 (flow forming process: F/F) 및 용접공정을 거쳐 시효경화후의 경도(HRC 48-52)가 높아 절삭가공 및 Tapping에 어려움이 있다고 판단되어 브라켓 밀링가공(Tapping포함)을 시효경화공정 이전에 완성하는 것으로 공정 FLOW를 설정하였으나, 시효경화 시 유동성형공정 잔류응력 및 재질특성에 의한 수축, 변형 등으로 도면상 요구된 품질(형상 및 위치공차) 만족이 미흡하였을 뿐만 아니라 오히려 전체 공정 수만 증가하였음. 따라서 연소관 및 Bracket 완성가공을 시효경화 후에 실시하는 것으로 공정 개선 하고자 시험 작업한 결과, 선삭, 밀링작업등 다른 기계가공 공정의 문제점은 대부분 해결할 수 있었으나, Tapping공정만은 해결할 수 없어서 진정한 공정개선을 기할 수 없었음. 그러나, 제품의 품질 및 생산성을 고려 시효경화 후 Tapping 공정실시 필요성이 강력히 대두되어 Maraging steel 재질특성에 적합한 공구 및 작업조건을 검토, 설정 시험작업 함으로써 공정개선을 이룰 수 있었음.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.7
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• pp.163-170
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• 2003

The back beam for a automotive bumper was roll formed to improve performance, reduce weight and save cost. For the back beams produced by conventional stamping and roll forming, the crashworthiness analyses were carried out by numerical simulation and real impact test. The characteristic properties and applicability of the roll formed back beam are discussed from the results of the analyses.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.249-257
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• 2001

본 논문에서는 경남 양산지역의 퇴적층에서 채취한 불교란 시료를 이용하여 표준압밀시험($IL_{CON}$)과 일정변형률(CRS, Constant Rates of Strain) 압밀시험을 수행한 후 각각의 시험결과를 분석하여 양산점토의 투수특성을 고찰하였다. 이를 위하여 투수계수와 간극비의 관계를 Kozeny(1927)와 Carman(1956) 이후 제안된 많은 연구결과와 비교, 검토하였으며, 시료를 연직방향으로 성형하여 CRS 시험을 수행한 후 횡방향투수계수를 산정하여 양산점토의 투수계수의 이방성을 살펴보았다. CRS시험 결과, 직접적으로 정상류를 발생시켜 누수계수를 측정하는 Rowe cell 시험에 비하여 상대적으로 투수계수의 이방성이 과소평가되는 경향을 보였다. 또한 현장 투수계수에 영향을 미치는 요소들을 살펴보고, 깊이에 따른 투수계수를 고찰하였다.다.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.259-267
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• 2001

실내시험으로 구한 점토의 공학적 성질은 샘플링, 운반, 저장, 그리고 성형과정 동안에 발생하는 시료의 교란으로 인해 원지반의 성질과 다르게 측정된다. 본 연구에서는 양산점토에 대한 삼축압축시험($CK_{o}$ UC) 결과를 이용하여 샘플링 방법에 따른 교란의 정도를 평가하였다. 실험에 사용된 시료는 76mm 튜브샘플러, 76mm 피스톤샘플러, 블록샘플러로 채취되었으며, 시료의 교란정도를 평가하기 위해 각 시료에서 측정된 체적변형률, 비배수 전단강도, Secant Youngs modulus, 그리고 파괴시 간극수압계수를 비교하였다. 시료의 교란정도를 평가하는 것 이외에도 SHANSEP 방법을 이용하여 수행한 $CK_{o}$ U 삼축압축시험 결과를 이용하여 양산점토에 대한 정규화 전단강도($C_{u}$ /$\sigma$$_{vc}$ )와 OCR 관계를 규명하였다. 또, 피에조콘 관입시험, 딜라토메타 시험, 그리고 현장 베인시험결과를 이용하여 구한 양산점토의 비배수 전단강도를 삼축압축시험 결과와 비교하였다.

• Journal of the Korean GEO-environmental Society
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• v.15 no.5
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• pp.67-74
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• 2014

In this study, a constant rate of strain test (CRS) and oedometer test was performed in order to study the consolidation characteristics to the liquid limit using a re-shaped clay which was preconsolidated at a constant pressure. Consolidation samples were made of kaolinite which was mixed with bentonite of 6 %, 9 %, 12 % and 15 % of it by weight and the test value of liquid limit of samples were appeared in 77 %, 84 %, 88 % and 91 % respectively. And then consolidation samples which were agitated sufficiently adding distilled water 2 times of liquid limit were preconsolidated in the condition of a constant pressure of 0.2 MPa. The oedometer test which is commonly used recently and the consolidation test of constant rate of strain which were applied in 0.001 %/min, 0.004 %/min, 0.01 %/min rate of strain according to ASTM, D4186-82 were performed and the preconsolidation pressures were compared and analyzed at 0.2 MPa preconsolidated pressure. As a result, in the case of low value of liquid limit, preconsolidation pressure was appeared same as 0.2 MPa preconsolidated pressure at the high speed strain rate, and in the case of high value of liquid limit, preconsolidation pressure was appeared same as 0.2 MPa preconsolidated pressure at the low speed strain rate.