• Journal of the Korean Ceramic Society
• /
• v.49 no.3
• /
• pp.236-240
• /
• 2012

The reticulated carbon foam have been used for their excellent properties in terms of thermal management which is getting important in industrial field currently. In this study, we measure the mechanical properties of the reticulated carbon foam which is heat-treated at various temperature from the prepared low-density phenol foam. Simultaneously, we observe microstructures with high resolution transmission microscope and measure the residual oxygen content of carbon foams to figure out the relationship between the apparent change of properties such as weight loss and linear shrinkage during heat treatment. In conclusion, the carbon foam heat-treated at $1400^{\circ}C$ shows the highest strength, and the mechanical behavior is believed to be strongly related to the creation of nano-size graphite crystals from the amorphous carbon during heat treatment. On the other hand, it is turned out that the weight loss occurred at the temperature under $1400^{\circ}C$ comes from the elimination of oxygen in the form of $CO_2$ or CO, but no evidence is found on weight loss mechanism at the temperature above $1400^{\circ}C$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1041-1042
• /
• 2006

High heat-resistant Al-Fe-V-Si and Al-Fe-V-Si-X rapidly solidified powder metallurgy (RS P/M) alloys have been developed under well-controlled high purity argon gas atmosphere. The $Al_{90.49}Fe_{6.45}V_{0.68}Si_{2.38}$ (at. %) RS P/M alloy exhibited high elevated-temperature strength exceeding 300 MPa and good ductility with elongation of 6 % at 573 K. Reduction of $H_2O$ partical pressure in P/M processing atmosphere led to improvement in mechanical properties of the powder-consolidated alloys under elevated-temperature service conditions. Ti addition to the Al-Fe-V-Si conduced to enhancement of the strength at room temperature. The tensile yeild strength and ultimate strenght were 545 MPa and 722 MPa, respectively.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2005.05b
• /
• pp.5-8
• /
• 2005

This research is to present experimental materials model of high strength concrete for prediction of fire safety of structural members based on mechanical properties of materials during heating up to 800$^{circ}C$. The following conclusions are drawn from this study. First of all, between 100 to 200$^{circ}C$, the high strength concrete show degradation at 100$^{circ}C$ and restoration at 200$^{circ}C$. The high strength concrete show elastic deformation at 20 - 200$^{circ}C$. Second, between 300 to 400$^{circ}C$, the mechanical properties of the high strength concrete which are exposed to fire show $75\~95\%$ as compared to the original properties because the thermally expanded ingredients of concrete, aggregates and cement paste, etc. Finally, beyond 600$^{circ}C$, the high strength concrete shows $75\~80\%$ reduction in thermal properties as compared to the normal concrete in the range of 600 to 800$^{circ}C$ and it shows $10\~30\%$ as compared to the original properties.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1997.10a
• /
• pp.117-124
• /
• 1997

In this study, mechanical properties of type V cement concrete with different curing temperature were investigated. The tests for mechancial properties, i.e., compressive strength and modulus of elasticity, were carried out on two kinds of type V cement concrete mixes. concrete cylinders cured at 10, 23, 35 and 50℃ were tested at 1, 3, 7 and 8 days. The 'rate constant model' was used to described the combined effects of time and temperature on compressive strength development. Test results show that concrete subjected to high temperature at early age attains greater strength than concrete to low temperature but eventually attains lower later-age strength than that. With type V cement concrete, the linear and Arrhenius rate constant models both accurately describe the development of relative strength as afunction of the equivalent age.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2007.11a
• /
• pp.95-98
• /
• 2007

This study investigates the mechanical properties of the high strength concrete in the region of 80MPa corresponding to the temperature and fiber content change. For the properties of the fresh, slump flow is $600{\pm}100mm$, and air content is $3.0{\pm}1.0%$. They satisfy each targets, and there was no difference for the each fiber types. As the propertied of the hardened concrete, the compressive strength at 28 days is indicated over 80MPa, and they are similar to the change of the fiber types. The residual compressive strength in response to the temperature change of the NY, PP, and NY+PP fiber at $200^{\circ}C$ are increased by 115, 114, and 110% on the standard condition, and it is suddenly decreased at $400^{\circ}C$. They are decreased by 33, 19, and 16% on the standard condition at $800^{\circ}C$.

• KIEE International Transactions on Electrophysics and Applications
• /
• v.4C no.2
• /
• pp.51-54
• /
• 2004

In this paper, the thermal and mechanical properties of elastic epoxy for the application of high voltage products were investigated. Glass transition temperature (Tg) of elastic epoxies cannot be found from room temperature to 20$0^{\circ}C$ by DSC (Differential Scanning Calorimetry). Weight reduction occurred at 285$^{\circ}C$ and 451$^{\circ}C$ according to a thermogravimeter. The first temperature was affected by addictives and the second by epoxies characteristic. Maximum tensile strain showed 28.3kgf/$\textrm{cm}^2$/$\textrm{cm}^2$ at 20% of mechanical stress in addictives 35 (phr). The SEM (Scanning electron microscope) micrograph of the fracture surface observed void and tearing of elastic epoxy at addictives 35 (phr). On the other side, the SEM micrograph of the rigid epoxy showed a broken trace.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.05a
• /
• pp.159-163
• /
• 2006

The effects of annealing temperature and time on mechanical properties and microstructures were studied in cold drawn pearlitic steel wires containing 0.84wt% Si. Annealing was performed from $200^{\circ}C$ to $450^{\circ}C$ with different time of 30sec, 1min, 15min and 1hr. The increase of tensile strength at low temperature was related with strain ageing. The decrease of tensile strength at high annealing temperature was related with spherodization of cementite and the occurrence of recovery of the lamellar ferrite in the pearlite. The improvement of ductility was connected with spherodization of cementite plate in pearlite and recovery process by reduction of high dislocation density at short time annealing temperature of $400^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.11a
• /
• pp.403-403
• /
• 2008

This article reports changes in the mechanical properties of chromium steel after nitrogen implantation at high temperature. The samples are implanted with 120keV N-ion at doses ranging from $1\times1080$ to $4\times1080ions/cm^2$ and at substrate temperature ranging from 25 to $400^{\circ}C$. Nano-hardness and AES(Auger electrons spectroscopy) were measured from nitrogen ion implanted layer. The sliding wear and impact wear properties of the implanted samples were also measured. The results revealed that the hardness and mechanical properties of ion implanted samples depend strongly on the ion doses and implantation temperature. The hardness of the nitrogen implanted sample with 120keV, $4\times10^{18}ions/cm^2$, $335^{\circ}C$ was measured to be approximately 20 GPa, which is approximately 5 times higher than that of un-implanted sample (H=3.8 GPa). Also, the sliding wear and impact wear properties of nitrogen implanted samples were greatly improved. Detailed experiment results will be presented.

• Laser Solutions
• /
• v.12 no.4
• /
• pp.12-16
• /
• 2009

The engineering ceramic is one of the materials advantageous in various conditions with high strength, endurance at high temperature, abrasion resistance and corrosion resistance, etc. However, due to high strength and high brittleness, ceramic incurs high costs and long time on finishing process required after sintering. So a process for obtaining wanted measurements of them has been studied using the high temperature which makes ceramics softened and heat affected recently. This study makes an estimate of laser-assisted machining (LAM) if an economically practical process for manufacturing precision silicon nitride ceramic parts using laser beam. In this study, mechanical properties of silicon nitride at high temperature were observed. And during the LAM, it was observed that cutting force and tool wear were reduced and oxidation of machined surface was increased according to a increase of laser power.

• Archives of Metallurgy and Materials
• /
• v.66 no.4
• /
• pp.971-975
• /
• 2021

This study investigates the effects of grain boundary structures on mechanical properties of nanocrystalline Al-0.7Mg-1.0Cu alloy using nanoindentation system. Grain boundary structure transforms to high angle grain boundaries from low angle ones with increase of heat treatment temperature and the transformation temperature is about 400℃. Young's modulus and hardness are higher in sample with low angle grain boundaries, while creep length is larger in sample with high angle ones. These results indicate that progress of plastic deformation at room temperature is more difficult in sample with low angle ones. During compression test at 200℃, strain softening occurs in all samples. However, yield strength in sample with low angle grain boundaries is higher twice than that with high angle ones due to higher activation energy for grain boundary sliding.