• 대한기계학회논문집A
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• 제38권6호
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• pp.649-653
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• 2014

대부분의 신뢰성 기반 최적설계는 최적설계 과정에서 설계점이 이동함에도 불구하고 설계변수의 불확실성은 변하지 않는다. 하지만 실제 문제에서 설계변수의 값에 따라 불확실성이 변하는 경우가 있다. 예를 들어 철판의 두께가 설계변수이고, 철판의 제작공차가 불확실성인 경우, 철판의 두께에 따라 철판의 제작공차가 달라지기 때문에 설계변수의 값에 따라 그 값의 불확실성이 변한다. 본 연구에서는 설계변수의 값에 따라 불확실성이 변하는 것을 변동 불확실성으로 정의하고, 이를 신뢰성 기반 최적설계에 적용하는 변동 불확실성을 고려한 신뢰성 기반 최적설계 기법을 제안한다. 수학예제에서 변동 불확실성을 고려하지 않은 신뢰성 기반 최적설계와 변동 불확실성을 고려한 신뢰성 기반 최적설계의 비교를 통해 제안한 방법의 필요성을 확인한다. 또한 엔진 크래들의 변동 불확실성을 고려한 신뢰성 기반 최적설계를 통해 제안한 방법의 유용성을 확인한다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.325-328
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• 2008

In recent years, developments of light weight vehicle are one of the most important issues in automotive industry. It is important to know the variations of the mechanical properties in the hydro forming process for the safe and durable design purposes. Generally, tube hydroforming process consists of three main processes such as bending, preforming, and hydroforming. It means that the strain hardening histories of final products are nonlinear. In this study, strain hardening behavior during hydroforming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and strength were used as an index of strain hardening during respective processes. The correlationship between strength and hardness obtained from tensile test has been equivalently converted into correlation between hardness and measured strain.

• 열처리공학회지
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• 제18권4호
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• pp.223-228
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• 2005

Tube hydroforming provides a number of advantages over conventional stamping process, including fewer secondary operation, weight reduction, assembly simplification, adaptability to forming of complex structural components and improved structural strength and stiffness. It can produce wide range of products such as subframe, engine cradle, and exhaust manifold. In this study, the effect of the heat treatment conditions such as post seam annealing (PSA) and bright annealing (BA) on the ovality and hydro-formability of steel tubes has been investigated. Hydroformabilities have been estimated by the bulging heights obtained at various processing parameters such as internal pressure, axial feeding and heat treatment conditions. The ovality and forming height are strongly influenced by material properties after heat treatments.

• 대한기계학회논문집A
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• 제31권8호
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• pp.833-838
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• 2007

In tube hydroforming process, several defective products could be obtained such as bursting, wrinkling, folding, buckling. Because, especially, bursting is most frequently occurred failure among the well known failures, it is mostly important to predict the onset of bursting failure on tube hydroforming process. For most sheet metal forming processes, strain based forming limit diagram(FLD) is used often as a criteria to estimate the possibility of onset of the failures proposed above. However, FLD has a shortcoming that it is dependent on strain path while stress based diagram is independent on strain history. Generally, tube hydroforming consists of three main processes such as pre-bending, pre-forming, and hydroforming and it means that the strain histories of final products are nonlinear. Therefore, forming limit stress diagram(FLSD) is more suitable to predict forming limit for hydroforming parts. In this study, FLSD is applied to estimate bursting failure for an engine cradle of an automobile part. Consequently, it is proved that application of FLSD to predict forming limit is available for tube hydroforming parts.

• 소성∙가공
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• 제17권1호
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• pp.52-58
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• 2008

Tube hydroforming process is generally consisted with pre-bending, preforming and hydroforming processes. Among forming defects which may occur in tube hydroforming such as buckling, wrinkling and bursting, the wrinkling and bursting by local instability under excessive tensile stress mode were mainly caused by thinning phenomenon in the manufacturing process. Thus the accurate prediction and suitable evaluation of the thinning phenomenon play an important role in designing and producing the successfully hydroformed parts without any failures. In this work, the formability on hydroformed part for automobile, i.e. engine cradle, was evaluated using finite element analysis. The initial tube radius, loading path with axial feeding force and internal pressure, and preformed configuration after preforming process were considered as the dominant process parameters in total tube hydroforming process. The effects on these process parameters could be confirmed through the numerical experiments with respect to several kinds of finite element simulation conditions. The degree of enhancement on formability with each process parameters such as initial tube radius, loading path and preform configuration were also compared. Therefore, it is noted that the evaluation approach of the formability on hydroformed parts for lots of industrial fields proposed in this study will provide one of feasible methods to satisfy the increasing practical demands for the improvement of the formability in tube hydroforming processes.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.187-190
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• 2009

Recently, automotive companies have invested in vehicle weight reduction and clean car development because of oil price rises and environmental problems. In particular, USA car makers have developed the vehicle spending 1 liter per 34km complying with PNGV(Partnership for a new generation of vehicle) and Europe car makers have developed the vehicle spending 3 liters per 100km. The USA government announced "The green car policy" in order to boost production of more fuel effective cars in 2009. According to the policy, it will be restricted to sell the car which spends more than 1 liter per 14.9km by 2020. To satisfy the current situations on automotive market, hydroforming technology has widely adapted vehicle structures such as engine cradle, chassis frame, A pillar, radiator support, etc. However, automotive companies have to consider formability and performance to improve and maximize the benefit from this technology in advance of detail design. The paper deals with one of the vehicle weight reduction methods using tube hydroforming technology and platform commonality in front suspension. FEA simulation is also introduced to evaluate hydro-formability and NVH performance at the beginning of design stage which is the best way to reduce the failure cost.

• 한국콘텐츠학회논문지
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• 제12권6호
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• pp.518-529
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• 2012

유럽의 통합은 1991년 12월 마스트리히트에서 유럽연합조약을 처음 체결하면서 시작되었다. 근대 민족 국가의 요람이라고 할 수 있는 유럽은 현재 각국들의 사회경제적 통합은 물론 정치적 분야에서도 단일 유럽을 실현해 왔다. 이러한 가운데 유럽연합의 새로운 통합성장동력을 개발하기 위한 평생교육정책은 무엇보다도 사회경제적 환경 변화에 대비 할 수 있는 교육적 대응이 필요하다고 보고 있다. 특히 평생교육분야의 협력과 통합발전에 있어서는 다양성과 상호 조절을 통한 효율성의 조화를 이루어야 하는 중요한 과제를 안고 있다고 본다. 그러나 그들의 노력에도 불구하고 2008년 이후 유럽연합의 몇몇 국가들은 경제 침체로 인하여 국가재정의 위기를 맞이하였으며, 급기야 유럽전체의 재정위기로 까지 영향을 미치고 있다. 이와 같은 위기는 현재 유럽연합의 사회경제적 통합을 흔들고 있다. 본 연구에서는 유럽연합의 사회경제적 통합을 위한 평생교육 체제구축 및 정책 추진 현황을 살펴보고, 유럽연합에 속한 국가들 간의 성인평생교육 참여율이 1인당 국민소득과 어떠한 관련성이 있는지 분석하고자 하였다. 그리고 유럽연합의 경제위기 속에서 회원국 간의 사회경제적 통합이 지속 가능할 수 있을지를 통합적 평생교육체제의 문제점을 중심으로 알아보았다. 또한 이를 통하여 우리나라 평생교육의 새로운 패러다임 전환과 정책 수립 및 발전 방향 제시에 시사점을 도출하고자 하였다.