• Journal of the korean Society of Automotive Engineers
• /
• v.18 no.5
• /
• pp.53-68
• /
• 1996

마그네슘이 자동차 경량화에 관심이 되는 이유는 근본적으로 CAFE 규제와 같이 경량화를 통한 화석연료의 소모를 크게 억제해야 한다는 사회적인 규제이나, 지난 10여년간의 기술발전으로 내식성이 나쁘다거나 취급이 위험한 금속이라는 인식이 크게 개선된 데에도 있다. 다른 경량금속에 대한 Mg 지금 가격의 비교조건이 호전되었고 향후 원소 재공급의 다변화가 추진되고 있는 것도 환경을 변화시킨 중요한 요인이다. 그간 중요한 경량화 대체 재료로 연구투자가 많았던 유기고분자 재료 및 FRP 등과 같은 복합재료는 폐기부품의 재활용이 어려움 때문에 호나경친화적인 단점이 부각되어, 이 소재의 증가가 주춤해 있다. 마그네슘의 경우에는 재활용이 가능하고, 진동흡수효과가 매우 커서 소음발생을 크게 줄일 뿐만 아니라, 주행 및 내구성시험에서 치수안정성이 좋고 많은 종류의 전자기기 사용에 의한 전자파 차폐효과도 큰 장점을 가지고 있다. 본 고에서는 Mg 다이캐스팅으로 자동차부품의 경량화 현황과 선진국에서 보는 전망을 미국을 중심으로 정리하고, 이와 관련한 Mg 다이캐스팅으로 자동차부품의 경량화 현황과 선진국에서 보는 전망을 미국을 중심으로 정리하고, 이와 관련한 Mg 기술적인 이슈와 시장전망도 서술하였다. 그리고 현재 우리나라의 연구계와 부품업계에서 추진하고 있는 연구개발 동향을 자동차 업계에 소개하는 의미도 있다. 이처럼 우리나라의 현황을 정리해 보는 것은 국내 자동차 산업이 국제적인 경쟁을 하고 있고 Mg기술과 원료확보에서 일본의 견제를 받고 있는 우리의 현실에서도 필요한 작업으로 생각된다.값들로 구성되는 형상을 내구 성능, 성형성등을 고려하여 최종 형상으로 결정한다. 내구성능의 예측은 금속부품의 내구수명 예측에 널리 이용되고 있는 방법이 방진 고무부품의 경우에도 적용 가능한지를 검토하고, 방진 고무부품에도 일반적으로 적용될수 있는 내구수명 예측방안의 개발 가능성을 타진해 보았다. 본 연구의 목표는 시제품을 제작하기 이전에 설계된 부품에 대한 스프링 상수 및 내구특성을 체계적으로 규명하여 제품 시험의 횟수를 줄이고, 보다 정밀한 제품을 제작할 수 있도록 하기 위한 것이다.세포수는 초기 배반포기배에서 팽윤 배반포기배로 진행됨에 따라 두배에서 세배 정도 증가되었음을 알 수 있었다. 또한, differential labelling과 bisbenzimide기법에서 얻어진 각각의 총세포수를 비교하였을 때 총세포수는 발달의 진행 정도에 따라 증가되며 그와 동시에 동일한 군 간의 세포수도 거의 유사함을 알 수 있었다. 따라서, ICM과 TE를 differential labelling하는 기법은 수정란의 quality를 평가하는데 매우 유용한 기법으로서 착상전 embryo 발달을 연구하는데 효과적으로 이용될 수 있다는 것을 시사한다. 고도의 유의차를 나타낸 반면 비수구, 초생수로구 및 Bromegrass 목초구 간에는 아무런 유의차가 인정되지 않았다. 7. 농지보전 처리구인 배수구와 초생수로구는 비처리구에 비해 낮은 침두 유출량과 낮은 토양유실량을 나타내었다.구보다 14% 절감되는 것으로 나타났다.작용하는 것으로 사료된다.된다.정량 분석한 결과이다. 시편의 조성은 33.6 at%

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.1
• /
• pp.51-56
• /
• 2012

Crashworthy fuel cells have been widely implemented to rotorcraft and rendered a great contribution for improving the survivability of crews and passengers. Since the embryonic stage of military rotorcraft history began, the US army has developed and practised a detailed military specification documenting the unique crashworthiness requirements for rotorcraft fuel cells to prevent most fatality due to post-crash fire. Foreign manufacturers have followed their long term experience to develop their fuel cells, and have reflected the results of crash impact tests on the trial-and-error based design and manufacturing procedures. Since the crash impact test itself takes a long-term preparation efforts together with costly fuel cell specimens, a series of numerical simulations of the crash impact test with digital mock-ups is necessary even at the early design stage to minimize the possibility of trial-and-error with full-scale fuel cells. In the present study a number of numerical simulations on fuel cell crash impact tests are performed with a crash simulation software, Autodyn. The resulting equivalent stresses are further analysed to evaluate a number of appropriate design parameters and the artificial neural network and simulated annealing method are simultaneously implemented to optimize the crashworthy performance of fuel cells.

• Journal of the Korean Vacuum Society
• /
• v.14 no.4
• /
• pp.215-221
• /
• 2005

Thermoelectric bismuth telluride thin films were prepared on $SiO_{2}$/Si substrate with co-sputtering of bismuth and tellurium targets. The effects of deposition temperature on surface morphology, crystallinity and electrical transport properties were investigated. Hexagonal crystallites were clearly visible at the surface of films deposited above $290 ^{\circ}C$. Change of dominant phase from rhombohedral $Bi_2Te_3$ to hexagonal BiTe was confirmed with X-ray diffraction analysis. The deviation from stoichiometric composition at high deposition temperature resulted in the change of structural and electrical characteristics. Seebeck coefficients of all samples have negative value, indicating the prepared $Bi_XTe_Y$ films are n-type thermoelectric. Optimum of Seebeck coefficient and power factor were obtained at the deposition temperature of $225 \^{circ}$C (about -55 $\mu$V/K and $3\times10^{-4}$ W/$k^{2}$m, respectively). Deterioration of thermoelectric properties at higher temperature.

• Korean Journal of Optics and Photonics
• /
• v.14 no.3
• /
• pp.312-320
• /
• 2003

The basic mechanistic aspects of the interaction and practical considerations related to polymer ablation were briefly reviewed. Photochemical and photothermal effects, which highly depend on laser wavelength have close correlation with each other. In this study, multi-scanning laser ablation processing of polymer with a DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO$_4$ laser (355 nm) was developed to fabricate a three-dimensional micro shape. Polymer fabrication using DPSSL has some advantages compared with the conventional polymer ablation process using KrF and ArF laser with 248 nm and 193 nm wavelength. These advantages include pumping efficiency and low maintenance cost. And this method also makes it possible to fabricate 2D patterns or 3D shapes rapidly and cheaply because CAD/CAM software and precision stages are used without complex projection mask techniques. Photomachinability of polymer is highly influenced by laser wavelength and by the polymer's own chemical structure. So the optical characteristics of polymers for a 355 nm laser source is investigated experimentally and theoretically. The photophysical and photochemical parameters such as laser fluence, focusing position, and ambient gas were considered to reduce the plume effect which re-deposits debris on the surface of substrate. These phenomena affect the surface roughness and even induce delamination around the ablation site. Thus, the process parameters were tuned to optimize for gaining precision surface shape and quality. This maskless direct photomachining technology using DPSSL could be expected to manufacture tile prototype of micro devices and molds for the laser-LIGA process.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.3
• /
• pp.72-83
• /
• 2022

This paper studied the effect on the microstructure, electrical properties, and compressive strength of cement mortar containing carbon fiber (CF) and steel fiber (SF), which are conductive materials. The resistivity of conductive fiber-reinforced cement mortar (FRCM) was measured using the 4-probe method, and the compressive strength was measured based on the compression test. Their performance was compared and reviewed with plain mortar (PM). Furthermore, the surface shape and composition of the fracture surface of the conductive FRCM were analyzed using a scanning electron microscope (SEM) and an energy disperse X-ray spectrometer (EDS). The results showed that the resistivity gradually increased as the curing time increased in all specimens, whereas the resistivity decreased significantly as the fiber volume fraction increased. Adding steel fibers up to 1.25% did not affect the resistivity of cement mortar considerably. On the contrast, the resistivity of carbon fiber was somewhat decreased even at low contents (ie, 0.1 to 0.3%), and thereafter, it was significantly decreased. The percolation threshold of the conductive CFRCM containing CF used in this experiment was 0.4%, and it is judged to be the optimum carbon fiber dosage to maximize the conductive effect while maintaining the compressive strength performance as much as possible. For the surface shape and composition analysis of conductive FRCM, the fracture surface was observed through SEM-EDS. These results are considered to be very useful in establishing the microstructure mechanism of reinforcing fibers in cement mortars.

• Journal of the Korean Wood Science and Technology
• /
• v.36 no.1
• /
• pp.61-68
• /
• 2008

The effect of rupture on the speed of ultrasonic wave was investigated with the PUNDIT and the effective detecting method of defects, moving transmitter and receiver. The speed of ultrasonic wave according to the course of rupture was not affected by transmitter and receiver and in the course of parallel rupture, but only in the course of vertical rupture. When rupture was not located on the ultrasonic wave progressing course, rupture was not detected. However, if rupture was formed perpendicularly to the ultrasonic wave progressing course but located on the ultrasonic wave progressing direction, rupture can be detected. Also, the rupture can be detected, when one transmitter and receiver was placed at top and the other at bottom. After detecting rupture in a part, rupture was determined accurately, placing and moving two transmitters and receivers at width.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.10 no.2
• /
• pp.139-152
• /
• 2008

A series of numerical experiments were carried out to simulate the rock cutting behavior by TBM disc cutter in a given took condition. AUTODYN-3D, a commercial program capable of simulating three-dimensional dynamic failure, was utilized to carry out the numerical tests over four different disc cutter spacing conditions. After modelling three-dimensional geometries of disc cutter and rock specimen, the linear cutting tests by a disc cutter were simulated for eight different types of rocks. The numerical result, that is the optimum cutter spacing for isotropic rocks had the good agreements with those from linear cutting test. However, for relatively anisotropic or jointed rocks, the specific energy obtained from the numerical tests was almost two-times bigger than the real linear cutting results. Therefore, to simulate cutting procedures for anisotropic rocks realistically, further studies would be necessary.

• Korean Journal of Materials Research
• /
• v.4 no.8
• /
• pp.921-926
• /
• 1994

The characteristics of gate oxide significantly depend on the last chemical solution used in cleaning process. The standard RCA, HF-last, SC1-last, and HF-only processes are the pre-gate oxide cleaning processes utilized in this experiment. Cleaning process was followed by thermal oxidation in oxidation furnace at $900^{\circ}C$. A 100$\AA$ gate oxide was grown and characterized with using lifetime detector, VPD AAS, SIMS, TEM, and AFM. The results of HF-last and HF-only were shown to be very effective to remove the metallic impurities. And these two splits also showed long minority carrier lifetimes. The surface and interface morphologies of the oxide were examined with AFM and TEM. The rough surface morphologies were observed with the cleaning splits containing the SC1 solution. The smooth surface and interface was observed with the HF-only cleaning process.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.5
• /
• pp.561-565
• /
• 2010

Stainless steel sheets are widely used as structural materials for the manufacture of railroad cars and commercial vehicles. These kinds structures used stainless steel sheets are commonly fabricated by using the gas welding. For the fatigue design of gas welded joints such as fillet joints and plug joints, it is necessary to obtain information on the stress distribution at the weldment and the fatigue strength of the gas welded joints. Moreover the influence of the geometrical parameters corresponding to the gas welded joints on the stress distribution and fatigue strength must be evaluated. ${\Delta}P-N_f$ curves were obtained from the data recorded in fatigue tests. Using these results, the ${\Delta}P-N_f$ curves were rearranged according the relation between $\Delta\sigma-N_f$ and the maximum stress at the edge of the fillet welded joint.

• Polymer(Korea)
• /
• v.36 no.6
• /
• pp.727-732
• /
• 2012

Baroplastic poly(butyl acrylate) (PBA)/polystyrene (PS) blends were prepared by mixing PBA and PS emulsions synthesized by cationic and anionic surfactant, respectively. Interestingly, the heterocoagulation of nanoparticles have found to be affected strongly by emulsion concentration but the blends have been prepared with almost same compositions regardless of the amount of reactants. Utilizing this method, PBA/PS/Si hybrid nano-blends were prepared successfully via electrostatic attraction forces between PBA, PS and silica nanoparticles. The hybrid nano-blend having 2 or 5 wt% of silica was then processed to a semi-transparent film at $25^{\circ}C$ under 13.8 MPa for 10 min, which showed 3.0 MPa of tensile strength and 25 MPa of elastic modulus. Therefore, the heterocoagulation technique can be used for preparing baroplastics with uniform compositions of polymer and silica nanoparticles.