• Composites Research
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• v.13 no.2
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• pp.81-90
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• 2000

For automotive applications, a sandwich sheet which was made of a 5182 aluminum alloy (AA5182) sheet and a polypropylene (PP) sheet, AA5182/PP/AA5182, has been developed. In order to evaluate its formability, the forming limit diagrams (FLD) of the 5182 aluminum alloy sheet with 0.2mm thickness and the sandwich sheet with 1.2mm thickness have been obtained based on the modified Marciniak-Kuczynski (M-K) theory. To account for the anisotropy of the sheet, Hill's 1948 yield function has been applied. The FLD of the sandwich sheet was predicted to be better than that of the AA5182 sheet, which was well confirmed by experiments.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.251-258
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• 2014

Sunroof tracks are manufactured by press-forming extruded aluminum sheets. During press forming, cracking occurs along the sharply bent edge. The final positions of the punch and die were measured on the section, and their relation to cracking was investigated. Finite element simulation of bending to the final position was done to find the critical strains. Three-point bending tests with different material orientations, hardnesses, bending edge lengths, and bending radii were carried out in the laboratory, and finite element simulation of the three-point bending tests was performed to find the critical strains.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.5 s.45
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• pp.1-10
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• 2005

This study proposes a fatigue reliability evaluation procedure for steel-composite high-speed railway bridge based on dynamic analysis and investigates the effectiveness of Tuned Mass Damper(TMD) in terms of the extension of fatigue life of the bridge. For the fatigue reliability evaluation, the limit state is determined using S-N curve and linear fatigue-damage accumulation. Dynamic analyses are peformed repeatedly to consider the uncertainties of train-velocity and damping ratio of the bridge. The distribution of random variables related to fatigue damage for the intended service life is then statistically estimated from analytical results. Finally, the fatigue reliability indices are obtained by means of the Advanced First-Order Second-Moment (AFOSM) method. Through numerical simulation of a steel-composite bridge of 40m span, the effectiveness of TMD on fatigue life of the bridge is examined and the results are presented.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.1
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• pp.127-130
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• 2010

This paper deals with the formability of DP590 steel considering the strain rate. The strain hardening coefficient, elongation and r-value were obtained from the static and dynamic tensile test. As strain rate increases from static to 100/s, the strain hardening coefficient and the uniform elongation decrease and the elongation at fracture and r-value decrease to 0.1/s and increase again to 100/s. The high speed forming limit tests with hemi-spherical punch were carried out using the high speed crash testing machine and high speed forming jig. The high speed forming limit of DP590(order of $10^2$/s) decreases compared to the static forming limit(order of $10^{-3}$/s) and the forming limit band in high speed forming test is narrower than that in the static forming test. This tendency may be due to the development of brittleness with increase of stain rate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.6
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• pp.277-282
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• 2007

The artificial lightweight aggregate (ALA) was manufactured using coal bottom ashes produced from a thermoelectric power plant with clay and, the sintering temperature and batch composition dependence upon physical properties of ALA were studied. The bottom ash (BA) had 13wt% coarse particle (>4.75mm) and showed very irregular shape so should be crushed to fine particles to be formed with clay by extrusion process. Also the bottom ash contained a many unburned carbon which generates the gas by oxidation and lighten a aggregate during a sintering process. Plastic index of green bodies decreased with increasing bottom ash content but the extrusion forming process was possible for the green body containing BA up to 40wt% whose plastic index and plastic limit were around 10 and 22 respectively. The ALA containing $30{\sim}40wt%$ BA sintered at $1100{\sim}1200^{\circ}C$ showed a volume specific density of $1.3{\sim}1.5$ and water absorption of $13{\sim}15%$ and could be appled for high-rise building and super-long bridge.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.20-20
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• 2012

최근, 수송기기 분야는 국제 환경규제 강화에 따른 CO2 절감, 연비향상, 경량화를 위한 기술적 수요가 증대되고 있으며, 그린카, 그린선박 등 친환경 수송기기에 대한 연구가 활발히 진행되고 있다. 하지만, 기존의 금속소재가 가지는 경량화의 한계를 극복하기 위해서는 CFRP, GFRP 등 금속대체 복합소재를 적용한 수송용 경량부품 개발에 대한 필요성이 요구되고 있다. 복합소재는 섬유사이에서 응력을 전달하는 기지(Matrix)와 하중을 전달하는 섬유(Fiber)의 종류와 양 및 적층 각도에 따라 수송용 부품에 적합한 기계적 특성을 얻을 수 있고, 높은 비강도와 비강성의 값을 갖게 되어 경량화가 용이한 장점이 있다. 반면, 섬유재의 종류, 성형방법, 경화온도 등에 따라 물리적 특성에 큰 변화가 발생하며, 수지의 경화조건에 따라 성형시간이 많이 소요되는 단점을 가지고 있다. 따라서, 본 연구에서는 자동차, 선박, 항공기, 철도차량 등 각종 수송기기의 경량화를 목적으로 생산성 향상 및 성형시간 절감을 위해 열가소성 수지, 저온속경화 수지를 적용하여, 경화 시간을 단축시키고, 3D-fabric 및 다층구조 직물을 Vacuum Infusion 공법으로 성형하여, 기존의 섬유재 적층시 소요되는 작업 공정을 간소화 할 수 있도록, 고속성형 복합소재를 적용한 수송용 경량부품 개발에 관한 연구를 수행하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.80-85
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• 2016

Carbon fiber-reinforced composite materials have been widely used in various industrial fields, but there are limits to increasing their strength and stiffness, because of the short-length fibers that are impregnated in them. In this study, a lab-scale small extruder system was developed with the capability to perform the carbon fiber impregnation and extrusion process in order to evaluate the properties of long-length carbon fiber reinforced thermoplastic composite materials molded by the LFT-D method. Specimens were made with the small extruder to press-mold long-length carbon fiber composite materials and evaluate their material properties. As a result, it was found that the carbon fiber length, press load and carbon fiber contents have a considerable influence on the strength and stiffness. Additional studies on such factors as the mixing screw design and coating of the carbon fiber are needed in order to improve the mechanical properties of carbon fiber composite materials.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.66-70
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• 2008

In this study, the formability of AZ31B magnesium alloy sheets was investigated by the analytical and experimental approaches. Tensile tests and limit dome height tests were rallied out at several temperatures between $25^{\circ}C$ and $300^{\circ}C$ to obtain the mechanical properties and forming limit diagram (FLD). The FLD-based criterion considering the strain-path and the blank temperature was used to predict the forming limit in a deep-drawing process of cross-shaped cup by finite element analysis. This criterion proved to be very useful in determining the optimal process conditions such as blank shape, punch velocity, minimum comer radius, fillet size, and so on, through the comparison between FEA and experimental data. In particular, the temperature of each tool that provided the best formability of the blank was determined by coupled temperature-deformation analyses. A practical method that can greatly reduce the forming time by increasing the punch speed during the forming process was suggested.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.1 s.173
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• pp.87-93
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• 2000

Warm, forming technique which is one of the new forming technologies to improve formability of sheet metal is applied to the cylindrical cup drawing of stainless-aluminum. clad sheets. In experiments the temperature of die and blank holder is varied from room temperature to 18$0^{\circ}C$, while the punch is cooled by circulation of coolant to increase the fracture strength of workpiece on the punch corner area. Test materials chosen for experiments are STS304-A1050-STS304, STS304-A1050-STS430 clad sheets and A1050-0 aluminum sheet. Teflon film as a lubricant is used on both sides of a workpiece. The limit drawing ratio as well as quality of drawn cups(distribution of thickness and hardness)are investigated and validity of warm drawing process is also discussed.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.1
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• pp.84-95
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• 1994

The effects of punch and blank shapes in the rectangular cup drawing process are examined experimentally to improve the formabilities. For this purpose, three blank shapes which are h-bl., G-bl., and T-bl., and five punch shape factors which are the ratios of two adjacent side lengths in rectangular cross section are adopted. The constructing methods of the three blank shapes are as follows. The h-bl. is designed by slip-line theory, and the G-bl. is selected for the similar shape to the punch. The T-bl. is obtained by the drawing method which is introduced in the technical references. The five punch shape factors are selected for length/width=1, 1.25, 1.5, 1.75 and 2. The experimental procedures are performed for all the above forming conditions to investigate and compare the formabilities. As a result, it is verified experimentally that the rectangular cups drawn by the h-bl. are more ideal than those drawn by G-bl. and T-bl.. They have not only higher limiting drawing ratio, more uniformity in drawn cup heights and more ideal thickness distributions, but also need relatively less maximum drawing forces.