• Korean Journal of Materials Research
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• v.10 no.5
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• pp.364-368
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• 2000

SiC fiber reinforced $Si_3N_4$ matrix composites combined with electrical conductive phases of carbon fiber and WC powder fabricated by hot pressing at 1773K. The ability to predict fracture in the ceramic matrix composites was evaluated by measuring simultaneous load-deflection and electrical resistanc difference-deflection curves in four point bending tests. The changes in electrical resistance differences closely corresponded to the fracture behavior of the composites. Different electrical conductive phases are suited to predicting different stages and rates of fracture. These obsevations how that it is possible to perform "in situ" fracture detection in ceramic composites.

• Journal of the Korea Furniture Society
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• v.12 no.2
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• pp.29-38
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• 2001

This study was carried out to develope a new process of flattening bamboo pieces(3 months old) by two steps of utilizing microwave oven and hot press. Internode bamboo pieces were impregnated with low molecular weight phenol formaldehyde resin (PF) under vacuum of 76 cmHg, heated in a household microwave oven in 1 minute, pressed on the temperature of $145^{\circ}C$ by the hot press for 10 minute, and then cooled by the cold press in their flattened form. The physical and mechanical . Properties of compressed flattened bamboo were as follows: 1) PF1(Mw:427) and PF2(Mw:246) sol. met the success of flattening of internode bamboo pieces in both of P. bambusoides and P. nigra var. PF2 showed the more plasticity to flatten the bamboo than PFI. The PF2 sol. with low molecular weight(Mw:246) gave the more weight gain than that of PF1 in the equal concentration. PF1 of 5% (NVC) and PF2 of 10% (NVC) sol. gave the best result for physical and mechanical properties and from a economical view point. 2) The PFI of 5% (NVC) sol. with low molecular weight decreased the water absorption of 62-63% and increased the bending strength (MaR) of 80-90%, compression strength of 43-54%. 3) The PF2 of 10% (NVC) sol. with low molecular weight decreased the water absorption of 56-57% and increased the bending strength (MaR) of 64-86%, compression strength of 39-63%.

• Journal of the Korean Society of Safety
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• v.38 no.2
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• pp.1-7
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• 2023

Fiber-metal laminates (FMLs) and polymer matrix composites (PMCs) are formed in various ways. In particular, FMLs in which aluminum is laminated as a reinforced layer are widely used. Also, glass fiber-reinforced plastics (GFRPs) are generally applied as fiber laminates. The bonding interface layer between the aluminum and fiber laminate exhibits low strength when subjected to hot press fabrication in the event of delamination fracture at the interface. This study presents a simple method for strengthening the interface bonding between the aluminum metal and GFRP layer of FML composites. The surfaces of the aluminum interface layer are engraved with three kinds of patterns by using the laser machine before the hot press works. Furthermore, the effect of the laser patterns on the interfacial toughness is investigated. The interfacial toughness was evaluated by the energy release rate (G) using an asymmetric double cantilever bending specimen (ADCB). From the experimental results, it was shown that the strip type pattern (STP) has the most proper pattern shape in GFRP/Al FML composites. Therefore, this will be considered a useful method for the safety assessment of FML composite structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.9
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• pp.957-962
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• 2009

Sialon was produced by hot-pressing the mixtures of $Si_3N_4$, AlN and $Y_2O_3$ powders. All fracture tests were performed on a three-point loading system with a 30 mm bending span. Fracture toughness and Vickers hardness of smooth specimen were average 7.05 $MPa{\cdot}m^{0.5}$ and Hv = 1580, respectively. Density of three kinds of specimens, smooth specimen, smooth and healed specimen, smooth with $SiO_2$ colloidal coating and healed specimen, had beyond 99 % of theoretical density. Bending strength of smooth healed specimens had high strength more than 1 GPa. Crack healed specimens recovered as strength as smooth specimen. That is, cracked specimen with $SiO_2$ colloidal coating on cracked part recovered strength by heat treatment, completely. Crack healing of $Si_3N_4$ composite ceramics had contributed glassy $SiO_2$ to strength recovery. Limiting high temperature for bending strength of heat treated smooth specimen for bending strength was about 1273 K.

• Corrosion Science and Technology
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• v.7 no.4
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• pp.224-232
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• 2008

During the hot rolling process, steels develop an oxide scale on their surface. This scale can affect the mechanical properties of the rolled steel and its surface aspect. The main problem comes from the mechanical integrity of the oxide scales which could delaminate or crack, leading eventually to later oxide incrustation within the steel. The objective of the present work is to qualify the mechanical integrity of the iron oxide scales during the hot rolling process. The laboratory experiments use a four point bending test to simulate the mechanical solicitation which takes place during the rolling sequence of the steel slabs. The oxide scales grow on a mild steel at $900^{\circ}C$ under wet or dry atmosphere and the oxidized steel is then mecahnically tested at $900^{\circ}C$ or $700^{\circ}C$. The high temperature four point bending tests are completed with microstructural observations and with the record of acoustic emission to follow in-situ the mechanical damages of the oxide scales. The results show the role of water vapor which promotes the scale adherence, and the role of the temperature as the oxide are more damaged at $700^{\circ}C$ than at $900^{\circ}C$.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.396-400
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• 2003

A new synthesis process for nano laminating Ti$_3$SiC$_2$ has been developed using TiCx (x=0.67) and Si powder as starting materials by a reaction hot pressing. Bulk Ti$_3$SiC$_2$ was fabricated using a green body consisting of TiCx and Si by a hot pressing under the pressures of 25 MPa at 1420-1550 $^{\circ}C$ for 90 min. The synthesized Ti$_3$SiC$_2$ was consisting of only TiCx and Ti$_3$SiC$_2$. The relative density of sintered bulk Ti$_3$SiC$_2$ was increased as the hot pressing temperature was increased, which was mainly due to the increase in TiCx contents in synthesized Ti$_3$SiC$_2$. The synthesized Ti$_3$SiC$_2$ bulk was consisted of nano sized lamella structure of 20-100 nm in thickness. It was found that TiCx particles in Ti$_3$SiC$_2$ would increase the 3-point bending strength of synthesized Ti$_3$SiC$_2$ bulk. The maximum 3-P. bending strength of synthesized Ti$_3$SiC$_2$ bulk was more than 800 MPa. The Vickers hardness of synthesized Ti$_3$SiC$_2$bulk was as low as 5 Gpa, which was decreased with the indentation load. The quasi-plastic deformation behaviors were observed around indentation mark on Ti$_3$SiC$_2$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.819-827
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• 1992

Investigations of the fatigue damage of roughing mill roll and experimentally. By the computer simulation for analysing the stresses on the roll surface and experimental hot rolling, the following results were drawn : The crakcs observed on the roll surface were initiated thermally in the initial stage of the rolling and propagated by repeated thermal and bending stresses. The size of the roll surface cracks smaller than 4.87mm could avoid the occurrence of tiny scab, surface defect of hot steel strip. Since the size of surface cracks observed on the roughing mill roll was very small, the fatigue damage of roll surface was found not to be the major factor for the formation of the scab.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.8
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• pp.847-854
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• 2007

The battery electrode of a mobile phone is made of layered polymer coated on aluminum foils and the hot rolling process is applied to increase the density per volume of an electrode for a high capacity battery. The flatness of batteries surfaces should be less than $2{\mu}m$. To satisfy the required flatness, the deformation of roll surface due to bending and heating of the roll should be minimized. Complicated hot oil paths of $100^{\circ}C$ inside the roll are required for heating the polymer layers. FEA was used to calculate thermal deformations and temperatures distributions of the roller. Based on FEA, a modified surface curvature called a crown roll was suggested and this gave the area of 30% improved flatness compared with a flat roll. The flat roll satisfied the flatness of $2{\mu}m$ in the length of 340 mm and the crown roll resulted in the longer length of 460 mm. Experiments to measure the temperature distribution and thermal strain were performed and compared with FEA. There were only 6% difference between two results.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.122-125
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• 2001

The objective of this research is to develop hybridized yarns for thermoplastic composites, and to examine tile effect of cooling rate on mechanical properties of the composites. The co-braided yarn utilizing carbon fibers as reinforcements and Nylon 66 fibers as matrix materials has been fabricated. Thermoplastic composites have been manufactured by the hot-press forming process. For the processing conditions, cooling rates of $-2.5^{\circ}C$/min and $-60^{\circ}C$/min have been considered. Three-point bending test and losipescu shear test were performed to investigate the effect of the cooling rate and the surface treatment of carbon fibers. SEM photographs were used to investigate the fracture surfaces of the tested samples. The cooling rate of $-60^{\circ}C$/min resulted in the higher strength and elastic modulus for bending and shear tests. The composites of the epoxy-sized carbon fibers showed the lowest strength due to the degradation of the sizing material during the thermoforming process.

• The Korean Journal of Ceramics
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• v.2 no.4
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• pp.212-215
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• 1996

This paper focuses the strength and wear resistance of CVD diamond films. The strength of free-standing CVD diamond films synthesized by microwave plasm CVD, DC plasma CVD, RF plasma CVD and arc discharge plasma jet CVD has been measured by three-point bending test. The wear resistance of CVD diamod films has been evaluated by the pin-on-disk type testing. diamond films coated on the base of sintered tungsten carbide pin by hot filament CVD have been rubbed with a sintered diamond disk in muddy water. Volume removed wear of CVD diamond has been compared with stellite, WC alloy and bearing steel.