• Advances in materials Research
• /
• 제13권2호
• /
• pp.129-140
• /
• 2024

This study evaluates the ratio of Toluene di-isocyanate (TDI) functional group isocyanate (NCO) to the binder functional hydroxyl group (OH) in HTPB/AP/Al-based propellants on their mechanical properties, flow rate, and viscosity to determine the limitations of NCO/OH in the composition of solid propellants. The propellants consisted of hydroxyl-terminated polybutadiene (HTPB) polyurethane (PU), aluminum (Al) and tri-modal ammonium perchlorate (AP). The tri-modal AP consisted of 30% of coarse AP, 30% of medium AP, and 8% of fine AP. The ratio of NCO/OH varies from 0.73 to 0.85, with two binder percentages of 10.5% and 12%. An increase in NCO/OH ratio with 10.5% binder provided 20%, 95%, and 8 to 9% increments in UTS, modulus, and hardness, respectively. However, the propellant elongation, density, and flow rate decreased by 170%, 0.2%, and 11-12%, respectively. Viscosity increased 20% based on initial hour reading. The 12% binder provides 27%, 47%, and 5~6% an increment of UTS, modulus and hardness respectively. However, the propellant elongation, density, and flow rate decreased by 47%, 0.17% and 27%, respectively. The viscosity increased 30% based on initial hour reading. This study suggests the NCO/OH value of 0.77 and 10.5~11% binder content in propellant based on the mechanical properties, flow rate, and viscosity for better processing and pot life.

• 한국주조공학회지
• /
• 제29권5호
• /
• pp.204-212
• /
• 2009

The effects of addition of magnesium only and the simultaneous addition of magnesium and aluminum on the graphite morphology of the cast iron with the composition of 3.6wt.% and 2.5wt.%Si poured into shell stack mold were investigated. The nodularity and mechanical properties of the specimen with smaller cross-section were higher than those with langer one, when copper was not added. When the magnesium only was added, the nodularity was decreased with decreased residual magnesium content and the C. V, graphite was obtained with the magnesium content in the range of 0.010~0.015wt.%. When the magnesium and aluminum were added together, the nodularity was decreased with decreased residual magnesium and increased aluminum contents. When copper was added, the volume fraction of pearlite in the matrix, strength and hardness were higher and elongation was lower for specimen with smaller cross-section. The volume fraction of pearlite, strength and hardness were increased and the elongation was decreased with increased copper content for the specimen with C, V, graphite.

• 열처리공학회지
• /
• 제30권6호
• /
• pp.271-278
• /
• 2017

This study was carried out to investigate the relationship between the mechanical properties and damping capacity of thermo-mechanical treated 316L stainless steel. Dislocations, ${\varepsilon}$ and ${\alpha}^{\prime}$-martensites were formed by thermo-mechanical treatment, and the grain size was changed from micrometer to sub-micrometer by 5-cycled thermo-mechanical treatment. The volume fraction of dislocations, ${\varepsilon}$ and ${\alpha}^{\prime}$-martensites was increased, and grain size of austenite increased and lengthened by the with increasing cycle number of thermo-mechanical treatment. In 5-cycled specimens, the volume fraction of ${\alpha}^{\prime}$-martensite was more than 25% and the less than 5% of volume fraction of ${\varepsilon}$-martensite was attained. With increasing number of thermo-mechanical treatment, hardness, strength and damping capacity were increased, but elongation was decreased. Damping capacity was increased with increased hardness and strength, but decreased with increased elongation, and this result was the opposite tendency for general metal.

• 동력기계공학회지
• /
• 제17권4호
• /
• pp.103-108
• /
• 2013

This study was investigated the effect of austenitizing treatment the microstructure and mechanical properties in modified 440A steel, and the results were as follows. The amount of remaining carbide decreases with increasing the austenitizing treatment temperature, and all carbide is completely dissolved at $1250^{\circ}C$. The amount of remaining carbide decreases with increasing the austenitizing treatment time, but the carbide remains insoluble up to 120 minutes at $1050^{\circ}C$. The strength and hardness gradually decrease with increasing the austenitizing treatment temperature and is significantly lower at $1250^{\circ}C$, while the elongation and the impact value rapidly increase. The strength and hardness rapidly decrease, the elongation and impact value rapidly insrease with increasing the austenitizing treatment time and exhibit no change at above 120 minutes. The austenitizing treatment modified 440A steel is required for temperature of above $1050^{\circ}C$ and time of above 60 minutes.

• Macromolecular Research
• /
• 제15권4호
• /
• pp.315-323
• /
• 2007

The present manuscript deals with the prediction of the lifetime of NBR compound based rubber gaskets for use as fuel cells. The material was investigated at 120, 140 and $160^{\circ}C$, with aging times from 3 to 600 h and increasing $H_2SO_4$ concentrations of 5, 6, 7 and 10 vol%. Both material and accelerated acid-heat aging tests were carried out to predict the useful life of the NBR rubber gasket for use as a fuel cell stack. To investigate the effects of acid-heat aging on the performance characteristics of the gaskets, the properties of the NBR rubber, such as crosslink density and elongation at break, were studied. The hardness of the NBR rubber was found to decrease with decreasing acid concentration at both $120\;and\;140^{\circ}C$, but at $160^{\circ}C$, the hardness of the NBR rubber increased abruptly in a very short time at different acid concentrations. The tensile strength and elongation at break were found to decrease with increases in both the $H_2SO_4$ concentration & temperature. The observed experimental results were evaluated using the Arrhenius equation.

• 한국재료학회지
• /
• 제21권6호
• /
• pp.303-308
• /
• 2011

The effect of heat treatment on the micro-structures and the mechanical properties of 0.002% boron added low carbon steel was investigated. The tensile strength reached the peak at about $880-890^{\circ}C$ with the rising quenching temperature and then the hardness decreased sharply, but the tensile strength hardly decreased. The tensile and yield strength decreased and the total elongation increased with a rising tempering temperature, but the tensile and yield strength sharply fell and the total elongation prominently increased from above a $400-450^{\circ}C$ tempering temperature. Tempered martensite embrittlement (TME) was observed at tempering condition of $350-400^{\circ}C$. In the condition of quenching at $890^{\circ}C$ and tempering at $350^{\circ}C$, the boron precipitates were observed as Fe-C-B and BN together. The hardness decreased in proportion to the tempering temperature untill $350^{\circ}C$ and dropped sharply above $400^{\circ}C$ regardless of the quenching temperature.

• 동력기계공학회지
• /
• 제14권2호
• /
• pp.84-89
• /
• 2010

The effect of forging condition on the microstructure and mechanical properties of 9Cr-1Mo heat-resisting steel was investigated. Microstructure of centrifugal casted 9Cr-1Mo heat resisting steel and forged heat resisting steel are consisted of martensite. With the increase of forging ratio, tensile strength and hardness increased, while elongation and impact value decreased. By increasing of forging starting temperature and finishing temperature, tensile strength and hardness increased, while elongation and impact value decreased. We obtained the optimum forging conditions as follow, forging ratio is 30%, forging starting temperature is $1200^{\circ}C$ and forging finishing temperature is $950^{\circ}C$.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2007년도 추계학술대회 논문집
• /
• pp.47-51
• /
• 2007

The present paper reports the life time prediction of Acrylonitrile-Butadiene rubber (NBR) fuel cell gasket materials as a function of operational variables like acid concentration, ageing time and temperature. Both material and accelerated acid-heat aging tests were carried out to predict the useful life of the NBR rubber gasket for use as a fuel cell stack. The acid ageing of the gasket compounds has been investigated at 120, 140 and $160^{\circ}C$, with aging times from 3 to 600 h and increasing acid ($H_2SO_4$) concentrations of 5, 6, 7 and 10 vol%. Material characteristics the gas compound such as cross-link density, tensile strength and elongation at break were studied. The hardness of the NBR rubber was found to decrease with decreasing acid concentration at both 120 and $140^{\circ}C$, but at $160^{\circ}C$ interestingly the hardness of the NBR rubber increased abruptly in a very short time at different acid concentrations. The tensile strength and elongation at break were found to decrease with increase in both the acid concentrate ion & temperature. The life time of the compounds were evaluated using the Arrhenius equation.

• Elastomers and Composites
• /
• 제44권3호
• /
• pp.308-314
• /
• 2009

n-Butyl acrylate, n-butyl methacrylate, acrylonitrile, glycidylmethacrylate, and allyl methacrylate를 사용하여 유화중합에 의해서 아크릴 고무를 합성하였다. 가교단량체의 첨가량을 일정하게 고정시킨 후 주단량체 중 acrylonitrile을 변량시켰을 때 중합체의 Tg가 acrylonitrile의 증가에 따라 증가하면서 무니 점도, 경도(Shore A), 인장강도가 증가하였다. 신장률은 acrylonitrile의 증가에 따라 체인의 유동성이 감소하면서 감소하였다. 가교 단량체인 glycidylmethacrylate의 순수한 중합체의 Tg는 약 $56^{\circ}C$로 중합 시 첨가량이 증가하면 중합물의 Tg는 증가하고, 무니 점도, 경도, 인장강도도 증가하며 신장율은 감소하였다. 이는 rheometer의 측정 결과 glycidylmethacrylate의 증가에 의한 가교밀도의 증가에 기인하는 것으로 판단되었다.

• 한국환경과학회지
• /
• 제19권3호
• /
• pp.365-370
• /
• 2010

In this study, we carried out the evaluation of EPDM(Ethylene Propylene Diene Monomer) reclaimed rubber mixing with natural rubber at various mixing ratio to reuse as rubber filler. The scorch time and moony viscosity was analyzed to evaluate the effect of cure behavior. And also, we analyzed the tensile strength, the elongation at break and cure time to evaluate the variation of cure behavior. As the results, the scorch time and optimal cure time was decreased according to the increasing of EPDM reclaimed rubber. However, the moony viscosity was increased at each mixing ratio. In case of the added EPDM reclaimed rubber was 20 phr(parts by weight per 100 parts by weight of rubber), the hardness and specific gravity was increased a little. The hardness and specific gravity was increased in rapidly under 40 phr of the added EPEM reclaimed rubber. The tensile strength and elongation at break of the compound of natural and EPDM reclaimed rubber was rapidly decreased compared with its natural rubber when the ratio of adding EPDM reclaimed rubber was over 40 phr.