• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 추계학술대회논문집
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• pp.325-328
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• 2004

This paper deals with void crushing behavior by ingot forging process which consists of sequential operations of upset forging and bloom forging. The predicted results of void crushing behavior by the simplified global-local method using F.E. analysis showed that the inherent void at the top region of the ingots remains incompletely crushed even after several forging operations. From the results of the hot upset forging test using the billets with drilled voids, it was found that the bonding efficiency of the void after forging process increases with an increase in deformation, and a decrease of initial diameter of voids.

• Steel and Composite Structures
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• 제21권3호
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• pp.605-628
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• 2016

The energy absorption characteristics of diamond core sandwich cylindrical columns under axial crushing process depend greatly on the amount of material which participates in the plastic deformation. Both the single-objective and multi-objective optimizations are performed for columns under axial crushing load with core thickness and helix pitch of the honeycomb core as design variables. Models are optimized by multi-objective particle swarm optimization (MOPSO) algorithm to achieve maximum specific energy absorption (SEA) capacity and minimum peak crushing force (PCF). Results show that optimization improves the energy absorption characteristics with constrained and unconstrained peak crashing load. Also, it is concluded that the aluminum tube has a better energy absorption capability rather than steel tube at a certain peak crushing force. The results justify that the interaction effects between the honeycomb and column walls greatly improve the energy absorption efficiency. A ranking technique for order preference (TOPSIS) is then used to sort the non-dominated solutions by the preference of decision makers. That is, a multi-criteria decision which consists of MOPSO and TOPSIS is presented to find out a compromise solution for decision makers. Furthermore, local and global sensitivity analyses are performed to assess the effect of design variable values on the SEA and PCF functions in design domain. Based on the sensitivity analysis results, it is concluded that for both models, the helix pitch of the honeycomb core has greater effect on the sensitivity of SEA, while, the core thickness has greater effect on the sensitivity of PCF.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권3호
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• pp.578-597
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• 2014

Understanding of 'spatial' pressure distribution is required to determine design loads on local structures, such as plating and framing. However, obtaining a practical 'spatial' pressure distribution is a hard task due to the sensitivity of the data acquisition frequency and resolution. High-resolution Pessure-Idicating Flm (PIF) was applied to obtain pressure distribution and pressure magnitude using stepped crushing method. Different types of PIF were stacked at each test to creating a pressure distribution plot at specific time steps. Two different concepts of plotting 'spatial' pressure-area curve was introduced and evaluated. Diverse unit pixel size was chosen to investigate the effect of the resolution in data analysis. Activated area was not significantly affected by unit pixel size; however, total force was highly sensitive.

• Composites Research
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• 제22권6호
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• pp.32-38
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• 2009

본 연구에서는 탄소, 케블라 및 탄소-케블라 하이브리드 등 4가지 소재로 제작된 원형튜브시편에 대한 에너지 흡수능력 및 파손모드를 평가하였다. 이를 위해, 본 연구에서 일방향 프리프레그를 이용해서 원형튜브 제작하고 10mm/min의 하중속도로 준정적 압축시험을 수행하였다. 시험을 통해 취성파괴모드로 압축되는 탄소/에폭시로 제작된 튜브가 가장 우수한 에너지 흡수 특성을 보인 반면, 좌굴에 의해 압축되는 케블라/에폭시 튜브가 가장 낮은 에너지 흡수특성을 보였다. 하이브리드 [$90_C/0_K$]튜브의 경우 국부좌굴모드에 의해 에너지를 흡수했으며 우수한 압축후 구조온전성 특성을 보였다. [$90_K/0_C$] 튜브의 경우 주 파손모드는 단층굽힘모드이고 압축후 구조온전성이 확보되지 못했다.

• 한국해양공학회지
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• 제9권1호
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• pp.36-46
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• 1995

빙판파괴 형태는 여러 모드의 합성이며 실제로 한 가지 양식으로 파괴되는 경우는 거의 일어나지 않는다. 이제까지 빙하중 해석 이론이나 방법은 한 가지 양식에 기준하는 것이었다. 이 논문에서는 합성모드로 빙판이 파괴될 때 해양구조물에 작용하는 빙하중 추정방법을 소개하여 모형 실험결과치와 그 결과를 비교하였다. 두 가지 합성모드에 대한 빙하중 추정방법인 비례파괴해석법 (Proportional Failure Method)과 국부경계해석법(Local Ice boundary Method)을 본논문에 소개하였으며, 이 두가지 방법과 함께 널리 알려진 Crushing 해석방법을 적용하여 정적 및 동적 구조물에 작용하는 빙하중을 산출/비교하였다. 동적구조물은 쇄빙선을 이용하였고, 쇄빙선이 SPM 터미널에 monopod로 연결되어있는 형태를 선택하였다. 모형 실험은 Finland의 Wartsila 실험실에서 실시 하였고, 이 실험을 통하여 쇄빙선에 작용하는 빙력 및 시간별 쇄빙선의 동적 움직임을 측정하였다. 이 논문에서는 위에서 소개된 세가지 방법으로 계산된 빙하중과 실험측정결과를 비교하였고, 이론적으로 추정한 쇄빙선의 운동을 실혐결과치와 비교하였다. Crushing방법으로 산출한 빙하중은 실제치보다 상당히 높았고, 비례파괴해석법은 Crushing 방법보다 정확한 결과를 보여주었으며, 국부경계해석법은 상당히 모형실험측정치와 가까웠다. 물론 쇄빙선의 움직임도 빙하중에 따라 변화가 심했고, 국부 경계해석법을 적용했을 때 실제 쇄빙선의 동적움직임을 가장 가깝게 추정할 수 있었다.

• Composites Research
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• 제22권4호
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• pp.1-12
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• 2009

본 논문에서는 복합재 원형튜브의 에너지 흡수 특성을 평가하기 위해 준정적 압괴실험을 시행하였다. 사용된 시편은 필라멘트 와인딩 공법으로 제작된 GFRP(유리섬유/에폭시수지) 원형 튜브이다. 복합재 튜브의 에너지 흡수 특성 분석을 위한 파라미터로서 튜브의 트리거메커니즘, t/D, 섬유배향각 등을 고려하여 그 특성을 비교하였다. 튜브의 형상 측면에서 튜브 직경이 커짐에 따라 delamination에 의한 국부좌굴 발생빈도가 증가하게 되어 불안정한 압괴모드가 발생하는데 이러한 현상은 섬유 배향각을 조정하여 안정적인 압괴모드를 도출할 수 있었다.

• 대한조선학회논문집
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• 제57권6호
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• pp.353-364
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• 2020

This paper presents the semi-analytical ice load calculation methods that are useful to simulate the ice-breaking process. Since the semi-analytical methods rely on the previously developed closed form equations or numerical analysis results, the user's exact understanding for the equations must be supported in order to use the methods properly. In this study, various failure modes of ice such as local crushing, in-plane splitting failure, out-of-plane bending failure and radial or circumferential cracking with rotation of the broken ice floe are considered. Based on the presented methods, the fracture modes were evaluated according to the size and thickness of ice. In addition, time series analysis for the ice-breaking process was performed on several ice conditions and the results were analyzed.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권2호
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• pp.209-218
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• 2017

Sea ice is the main factor affecting the safety of the Arctic engineering. However, traditional numerical methods derived from classical continuum mechanics have difficulties in resolving discontinuous problems like ice damage. In this paper, a non-local, meshfree numerical method called "peridynamics", which is based on integral form, was applied to simulate the interaction between level ice and a cylindrical, vertical, rigid structure at different velocities. Ice in the simulation was freshwater ice and simplified as elastic-brittle material with a linear elastic constitutive model and critical equivalent strain criterion for material failure in state-based peridynamics. The ice forces obtained from peridynamic simulation are in the same order as experimental data. Numerical visualization shows advantages of applying peridynamics on ice damage. To study the repetitive nature of ice force, damage zone lengths of crushing failure were computed and conclude that damage zone lengths are 0.15-0.2 times as ice thickness.

• Structural Engineering and Mechanics
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• 제19권5호
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• pp.581-602
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• 2005

In this paper the accumulation of local damage during the cyclic loading in reinforced high-strength concrete columns is experimentally investigated. Two identical column specimens with annular cross-section and spiral reinforcement were designed and two tests, up to failure, under the action of a constant vertical concentrated force and a time-dependent concentrated horizontal force, were carried out at the LNEC shaking tables facility. Sine type signals, controlled in amplitude, frequency and time duration were used for these experiments. The concept of local damage based on local stiffness degradation is considered in detail and illustrated by experimental results. The specimens were designed and reinforced in such a way that the accumulation of damage was predicted by dominating deformations (cracking and crushing of the concrete) while the increasing of the loading values was a dominating factor of damage. It was observed that the local damage of HSC columns has exposed their anisotropic local behaviour. The damage accumulation was slightly different from the expected in accordance with the continuum damage concept, and a partial random character was observed.

• 한국환경농학회지
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• 제27권2호
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• pp.205-210
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• 2008

Life cycle assessment(LCA) is acknowledged as a valuable tool to quantify the environment impact of agricultural practice as well as final product(biodiesel) considering whole life cycle of the target product. As a preliminary research of LCA study for rapeseed(Brassica napus L.) biodiesel, the methodological issues which have to be regarded with high priority were dealt with. No life cycle inventory(LCI) based on local data are currently available for LCA of rapeseed cultivation, crushing, and conversion to rapeseed methyl ester(RME) in Korea. In this paper, the life cycle of rapeseed and methodological factors which have to be measured for building LCI of each process are provided and discussed, which are including seed, fertilizer, energy use in rapeseed cultivation environment; and crushing, RME conversion, and transportation in biodiesel production.