• 소성∙가공
• /
• 제20권4호
• /
• pp.309-315
• /
• 2011

The behavior of metallic materials at high strain rates shows different characteristics from those in quasi-static deformation. Therefore, the strain rate should be considered when simulating crash events. The objective of this paper is to evaluate the dynamic tensile characteristics of SPRC440 as a function of the volume fraction of phases. As-received SPRC440 is composed of ferrite and pearlite phases. However, ferrite and martensite phases were observed after heat treatment at $730^{\circ}C$ and $780^{\circ}C$ for 5 minutes, as expected by calculations based on the curves from dilatometry tests. High cross-head speed tensile tests were performed to acquire strain-stress curves at various strain rates ranging from 0.001 to $300\;s^{-1}$, which are typical in real vehicle crashes. It was observed that the flow stress increases with the strain rate and this trend was more pronounced in the as-received specimens consisting of ferrite and pearlite phases. It is speculated that the dislocation density in each phase has an influence on the strain rate sensitivity.

• 한국수산과학회지
• /
• 제19권6호
• /
• pp.575-580
• /
• 1986

1986년초 저자들은 불임 3배체 무지개송어의 대량 생산을 위하여 수정난을 $27^{\circ}C$로 열처리하였다. 그 결과 $50\%$ 전후의 3배체 무지개송어가 유도되었으며 유도된 3배체 송어의 초기 성장률은 여타 보고들과 같이 정상 2배체와 유사하였다. 앞으로 본 방법을 수정개량하여 처리함으로써 산업적으로 중요한 불임 무지개송어의 생산성을 높일 수 있으리라 사료된다.

• 한국환경보건학회지
• /
• 제30권2호
• /
• pp.133-139
• /
• 2004

The objective of this study was to investigate the destruction efficiency and to determine the fundamental parameters of oxidation kinetics under the supercritical water(SCW) condition. Target material was cephradine, toxic and antibiotic material, in the pharmaceutical wastewater. For this purpose, the effect of reaction temperature and oxidant were investigated on the destruction efficiency of cephradine. And the oxidation kinetics of cephradine was derived by using a empirical power-law model. The experiment was carried out in a cylindrical batch reactor made of Hastelloy C-276 which was endurable high temperature and pressure. The destruction efficiency of cephradine increased with increment of the temperature and reaction time. Also the type of oxidants was effected and oxidants(Air and $H_2O$$_2$) were enhanced the destruction efficiency. The global oxidation kinetics for cephradine has led to two rate expressions according to type of oxidant. - In the presence of air oxidant: Rate=k. $e^{-Ea}$RT/(Ceph.)$^{1.0}$ ( $O_2$)$^{0.51}$$\pm$0.05(k=3.27${\times}$$10^{5}$ sec. Ea=63.25 kJ/mole) - In the presence of $H_2O$$_2$ oxidant : Rate=kㆍ $e^{-Ea}$RT/(Ceph.)$^{1.0}$ ($H_2O$$_2$)$^{0.62}$$\pm$0.02(k=2.76${\times}$$10^4$/sec. Ea=47.65 kJ/mole)ole))

• 대한기계학회논문집A
• /
• 제20권4호
• /
• pp.1241-1250
• /
• 1996

The characteristics of fatigue cumulative damage and fatigue life of 8-harness satin woven CFRP composites with a circular hole under constant amplitude and 2-level block loading are estimated by Stochastic Makov chain model. It is found in this study that the fatigue damage accumulation behavior is very random and the fatigue damage is accumulated as two regions under constant amplitude fatigue loading. In constant amplitude fatigue loading the predicted mean number of cycles to a specified damage state by Markov chain model shows a good agreement with the test result. The predicted distribution of the fatigue cumulative damage by Markov chain model is similar to the test result. The fatigue life predictions under 2-level block loading by Markov chain model revised are good fitted to the test result more than by 2-parameter Weibull distribution function using percent failure rule.

• 한국표면공학회지
• /
• 제41권3호
• /
• pp.114-120
• /
• 2008

The pyrolysized carbon xerogel and aerogels were prepared from the sol-gel polymerization of resorcinol-formaldehyde(RF) followed by the dry process under ambient pressure and supercritical carbon dioxide condition respectively. The thermal behaviour of RF polymer xerogel was investigated with TGA analyzer to correspond with the pyrolysis process. The surface properties such as particle size, morphology and the point of zero charge of the pyrolysized porous carbon aerogels were studied for the precious metal catalyst supported media. It was found that the volume of the polymer aerogel decreased because of the significant linear shrinkage and weight loss of polymer gel during the carbonization. The point of zero charge of the carbon aerogel pyrolysized at $1050^{\circ}C$ under inert gas flow was about 10.

• Journal of Welding and Joining
• /
• 제16권3호
• /
• pp.157-166
• /
• 1998

Recently as environmental pollution caused by Pb has posed a serious threat to the global environment, the trend to regulate the usage of Pb in electronic industry is one the rise. Currently, the solder alloy with high Pb content, Sn-37%Pb, is utilized in the electronic assembly therefore, the objective of this study is to develop an alternative solder alloy for the existing Sn-37%Pb solder alloy. First thing, this work choosed Sn-5%Pb-1.5%Ag, Sn-5%Pb-1.5%Ag-x%Bi(x=1~5%) for candidate solder alloys, and examined their properties such as melting range, wettability, microhardness, tensile property, oxidation behavior and microstructure. Wettability was on the same level of Sn-37%Pb. Dissolution of Pb ion in Sn-5%Pb solder was 0.46ppm. This solder alloy revealed cellular dendrite microstructure $\beta$-Sn matrix, Pb-rich phase, Ag/Sn, and Cu/Sn Intermetallic compounds. The range of solidification temperature was within 3$0^{\circ}C$. Also these alloy displayed higher tensile strength and lower elongation than Sn-37%Pb. The resistance of oxidation in Sn-5%Pb-1.5%Ag solder alloy was superior to that of Sn-37%Pb solder alloy. But that of Sn-5%Pb-1.5%Ag-5%Bi solder alloy was equal to that of Sn-37%Pb solder alloy.

• 한국재료학회지
• /
• 제15권9호
• /
• pp.594-597
• /
• 2005

The barrier characteristics of ZrN films deposited by remote plasma enhanced atomic layer deposition(PEALD) using TDEAZ and $N_2$ remote plasma have been investigated under various deposition conditions such as temperatures, plasma power and processing pressures. ZrN films showed generally improved properties as the processing temperature, pressure and plasma power increased. The optimized processing temperature, plasma power and pressure were $300^{\circ}C$, 200 Watt and 1 torr. respectively ZrN films deposited at the optimized processing conditions showed the carbon contents and resistivity of $6at.\%$ and $400{\mu}{\Omega}cm$ respectively.

• 한국재료학회지
• /
• 제7권6호
• /
• pp.453-459
• /
• 1997

용탕단조법에 의해 제조된 Mg-9AI-2Zn 합금을 미세조직관찰, 미소경도측정, 인장시험 등을 행하여 시효거동과 기계적 성질을 조사하였다. 용탕에 가압을 한 결과 주조결함이 제거된 미세한 주조조직을 얻었으며 미세조직은 초정 $\alpha$(Mg 고용체), 과포화고용체 $\alpha$상 및 $\beta$(Mg$_{17}$AI$_{12}$)화합물의 3가지 상으로 구성되어 있었다. 16$0^{\circ}C$및 20$0^{\circ}C$에서 시효열처리한 결과 $\beta$석출물에 의한 피크 경도값이 나타났으며 피크경도에서의 석출물의 형태는 lamella 형태의 불연속 석출물이 대부분이었고 과시효에 따라 불연속석출물의 조대화와 함께 연속석출물의 분율이 증가하였다. 용탕단조방법에 의해 제조된 Mg-9AI-2Zn 합금의 인장특성은 인장강도 261.4MPa, 연산율 7.6%로서 상용 AZ 92 합금보다 인장강도 및 연신율에서 우수한 기계적 성질을 가졌는데 이는 Zn의 고용강화 및 용탕의 가압에 의한 효과였다.다.

• 한국재료학회지
• /
• 제16권11호
• /
• pp.663-667
• /
• 2006

CTAB(cetyltrimethylammonium bromide)-capped CdSe nanoparticles were prepared by using a 4 : 1(v/v) distilled water-isopropyl alcohol mixture. The cadmium chloride and sodium selenosulfate were used as the cadmium and selenium source. By the analysis of XRD and XPS, the resultant particle was confirmed to be cubic CdSe phase. TEM image showed CdSe nanoparticles with empty core. The CTAB-capped sample showed an maximum absorption at 418nm, blue-shifting compared with bulk CdSe, which indicated stronger quantum confinement effect compared with uncapped sample. From FT-IR analysis, it was found that the presence of the new peaks in the $850{\sim}1250cm^{-1}$ range indicated the existence of chemical bonding between CTAB and surface of CdSe nanoparticles. Also TG analysis indicated that there were two weight-loss steps for the CTAB-capped CdSe nanoparticles. It was suggested that CTAB played a significant role in protecting CdSe nanoparticles.

• 한국재료학회지
• /
• 제6권11호
• /
• pp.1074-1081
• /
• 1996

Mg-8Li-4AI 합금의 부식특성에 미치는 Y의영향을 전기화학적 분극시험 및 침지시험을 통하여 조사하였다. 전기 화학적 분극시험에서는 Y첨가량이 증가함에 따라 활성화 영역이 감소하엿고 부식전위가 증가하였으며, Y이 4.08wt% 첨가된 경우가 Y이 첨가되지 않은 경우에 비해 부식속도가 크게 감소하였다. 침지시험에서도 Y의 첨가량이 증가함에 따라 Y을 첨가하지 않은 시편에 비하여 무게감량 및 부시속도가 감소하였으며, Y이 첨가되지 않은 합금의 부식속도는 침지시간에 따라 급격히 증가하였지만 Y이 첨가되지 않은 합금의 부식속도는 침지시간에 따라 급격히 증가하였지만 Y이 4.8wt% 첨가된 합금은 96시간 이후부터 더 이상 증가하지 않았다. 이러한 결과는 Y 화합물(Mg24Y5)이 $\alpha$/$\beta$계면에서 희생 양극으로 작용하였기 때문이라고 생각된다. 따라서 Y의 첨가는 Mg-Li-AI 합금의 내식성을 향상시키는 역할을 한 것으로 판단된다.