• Composites Research
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• v.36 no.4
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• pp.281-287
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• 2023

Environmental pollution from waste and the climate crisis, due to rising global average temperatures, are reaching critical levels threatening human survival. Research is ongoing across various fields to solve this problem, with a key focus on developing eco-friendly, carbon-neutral materials. Our study aimed to integrate natural fibers, known for their environmentally friendly properties and lower carbon emissions, with carbon fibers. In general, combining high-strength and low-strength materials results in intermediate properties. However, we found that certain properties in our study exceeded those of typical carbon fiber composite materials. To validate this, we produced both carbon fiber composite materials and carbon fiber/natural fiber hybrid composite materials. We then compared their mechanical properties using a range of specific tests. Our results revealed that the hybrid composite material exhibited superior bending strength and fracture toughness compared to the carbon fiber composite material. We also identified the underlying mechanisms contributing to this strength enhancement. This breakthrough suggests that the use of hybrid composite materials may allow the production of stronger structures. Moreover, this can play a significant role in mitigating environmental pollution and the climate crisis by reducing carbon emissions, a major contributing factor to these global challenges.

• Journal of the Korean Ceramic Society
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• v.35 no.9
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• pp.939-944
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• 1998

The formation microstructure and properties of novel ceramic composite materials by active filler con-trolled polymer pyrolysis were investigated. Polymethlsiloxane filled with W is of particular interested be-cause of the formation of ceramic bonded hard materials (WC-$W_{2}C$-$S_{1}OC$) for wear resistant applications. Highly metal-filled polymer suspensions were prepared and their conversion to ceramic composites by an-nealing in $N_{2}C$ atmosphere at 1000-$1600^{\circ}C$ were studied. Dimensional change porosity and phase distribution (filler network) were analyzed and correlated to the resulting material properties. Microcrystalline com-posites with the filler reaction products embedded to the resulting material properties. Microcrystalline com-posites with the filler reaction products embedded in a silicon oxycarbide glass matrix were produced. De-pending on the pyrolysis conditions ceramic composites with a density up to 95 TD% a hardness of 7-8.8GPa Yong's modulus of 220-230 GPa a fracture toughness of 6-6.8$MPam^{1/2}$ and a flexual strength of 380-470 MPa were obtained.

• Journal of the Korea Institute of Building Construction
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• v.16 no.3
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• pp.279-288
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• 2016

The fundamental performance of any construction material should cover at least two phases: safety and serviceability. Safety commonly represents adequate strength, while serviceability encompasses the control of cracking and deflections at service loads. With respect to rapid hydraulic binders as a construction material, the above two phases should also be considered. Recent research on rapid cooling ladle furnace slag (RC-LFS) has drawn much attention, particularly given that it shows remarkable rapid hydraulic ability to pulverize to a fineness of $6,300cm^2/g$. This industrial byproduct could contribute to developing the sustainability of the rapidly hardening cementitious material system. This paper aims to expand upon the applicability of an RC-LFS-based binder that is composed of two parts. It also seeks to illustrate the engineering performance of an RC-LFS-based hybrid fiber-reinforced composite and to increase the strength of the RC-LFS-based composite. Each step of this experiment followed ASTM standards. The engineering performance, in both fresh state and hardening state, was tested and discussed in this paper. According to the experimental results for fresh concrete, the air content increased following the addition of polypropylene fiber. For hardened concrete, the toughness and strength improved following the addition of a hybrid fiber. The hybrid fiber mixture, which contains 0.75% of steel fiber and 0.25% of polypropylene fiber, shows even better engineering performance than other mixtures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.75-82
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• 1987

It is the objective of this study to estimate J-integral by numerical analysis, in which J-integral as aparameters in fracture mechanics can be used to evaluate unstable ductile fracture which is a important problem with respect to structural stability when the scope is beyond small scale yielding criteria. For this, 8-node isoparametric singular element as crack tip element of a cracked material was used to solve plastic blunting phenomenon at crack tip, and crack opening was forced to start when J-value was exceeding fracture toughness $J_{IC}$ of the material. And crack propagation behaviour was treated by using crack opening angle. From this study, it was shown that crack opening, stable propagation and unstable opening point of the cracked material found by using J-value obtained from this study were accord with the other study, so think, J-value obtained from this study can be directly used as a parameter in fracture mechanics to deal with the problem of stable propagation of crack and unstable ductile fracture.

• Journal of the Korean Wood Science and Technology
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• v.45 no.1
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• pp.53-61
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• 2017

In this study, specimens were produced with a column member and a wooden gusset only by inserting an wooden gusset which is a substitute for steel plate into the center of a slit-processed column member. The moment resistance performance of the specimens was compared with that of control specimens that used a steel plate. The measured maximum moments of the specimens produced with GFRP-reinforced wooden laminated gussets and pins were lower by 24% on average compared to the steel plate-inserted specimens, but they showed good toughness. The fracture shape suggests that it was fractured along the annual rings between the pin and the end of the column member. The rigid specimen that integrated a laminated wood and a wooden laminated gusset with adhesive showed 2.8 times greater initial rigidity and 40% greater maximum moment on average compared to the control specimen. The rigid specimens mainly fractured on a glulam around glue line.

• Proceedings of the SCSK Conference
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• 2003.09a
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• pp.469-479
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• 2003

A novel branched wax has been developed for the control of the hardness of oil-wax gels. Using this wax, glossier application and smoother texture but tough lipstick can be obtained. Oil-wax gels are oily solids composed of liquid and crystalline solid oils (waxes). They are widely used in various cosmetic products, especially lipsticks. The control of gel hardness is one of the most important techniques in improvement of the lipstick quality. Addition of small amounts of commercial branched paraffin wax (e.g. microcrystalline wax, b-PW) to n-paraffin wax (n-PW) has been commonly used to increase gel hardness. However, gel hardness is very sensitive to the quantity of b-PW and the gel obtained is not always hard enough for practical use. In this study we examined the relationship between the gel hardness and the properties of the wax crystal in the gel. We have found that, when b-PW is added to n-PW, the wax crystal size becomes smaller (hardening the gels) and its crystallinity is decreased (softening the gels) simultaneously. Considering this result, we have developed a novel branched wax, Bis(polyethylenyl)- tetramethyldisiloxane (named ESE). ESE molecules are composed of a central tetramethyldisiloxane unit (branch unit) with polyethylene units at both ends. The central unit may suppress crystal growth while the ends are expected to prevent a decrease in wax crystallinity during crystallization. When ESE is added to n-PW, the wax crystal obtained becomes smaller without decreasing in crystallinity; consequently, the gel hardness is dramatically increased. By using ESE, the total amount of wax in a lipstick can be decreased by 30％ without spoiling the stick toughness, thereby achieving glossy application and smooth texture.

• Journal of the Korean Ceramic Society
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• v.45 no.2
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• pp.105-111
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• 2008

Symmetric three layer composites have been prepared by freeze casting and then pressureless sintered at $l700-1800^{\circ}C$ in $N_2$ gas atmosphere. The relative sintered density of multilayer composites having microstructural characteristics of later intermediate-stage densification increased with sintering temperature and reached about 95% theoretical value at $1800^{\circ}C$. Although the indentation strength of the multilayer composites was generally reduced with increasing Vickers indentation load up to 294N, the damage resistance of multilayer composites was superior compared to monolithic layer 95AL/5SN material. The three-point bend strength of the layered materials remained at the values 266-298 MPa after indentation with a load of 49N, while that of the monolithic 95AL/5SN material was 219 MPa. The fracture toughness of the multilayer material was $5.4-6.6\;MPa\;m^{1/2}$.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.49-54
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• 2000

Cr-Mo-V steel is widely used as a material for the turbine structural component in fossil power plants. It is well known that this material shows the various material degradation phenomenons such as temper embrittlement, carbide coarsening. and softening etc. or ins to the severe operation conditions as high temperature and high pressure. These deteriorative factors cause tile change of mechanical properties as reduction of fracture toughness. Therefor it is necessary to evaluate tile extent of degradation damage for Cr-Mo-V steel in life assessment of turbine structural components. In this paper. the electrochemical potentiokinetic reactivation(EPR) test in $50wt%-Ca(NO_3)_2$ solution is performed to develop the newly technique for degradation damage evaluation of Cr-Mo-V steel. The results obtained from the EPR test are compared with those in small punch(SP) tests recommended by semi-nondestructive testing method using miniaturized specimen. The evaluation parameters used in EPR test are tile reactivation current density$(I_R)$ and charge$(Q_{RC})$ reactivation rate$(I_R/I_{Crit},\;Q_R/Q_{Crit})$. The results suggest that $I_R/I_{Crit}$ in these parameters shows a good correlation with SP test results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1127-1132
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• 2013

The failure of reactor internals may have a significant effect on the safe operation and shutdown of a reactor. Various agings related to neutron irradiation occur or can potentially occur in the reactor internals owing to high neutron irradiation levels. Austenitic stainless steel, one of the principal materials constituting the reactor internals, shows different mechanical material behaviors such as tensile/creep properties and fracture toughness with neutron irradiation levels. This variation should be considered when the structural integrity of the reactor internals against agings during the design lifetime or continued operation period is evaluated. In this study, user subroutine programs considering the variation of mechanical material behaviors with neutron irradiation levels were developed. The programs were validated by testing them for various conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.5
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• pp.550-555
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• 2007

The effective fracture toughness testing of materials intended for application in Micro Electro Mechanical Systems (MEMS) devices is required in order to improve understanding of how micro sized material used in device may be expected to perform upon the micro scale. ${\gamma}$-TiAl based materials are being considered for application in MEMS devices at elevated temperatures. Especially, in Alloy 4, both ${\alpha}_2$ and ${\gamma}$ lamellae were altered markedly in 3,000 h, $700^{\circ}C$ exposure. Parallel decomposition of coarse ${\alpha}_2$ into bunches of very fine (${\alpha}_2+{\gamma}$) lamellae. Parallel decomposition of coarse ${\alpha}_2$ into bunches of very fine (${\alpha}_2+{\gamma}$) lamellae. The materials were examined 2 types Alloy 4 on heat exposed specimen($700^{\circ}C$, 3,000 h) and no heat exposed one. Micro sized cantilever beams were prepared mechanical polishing on both side at $25{\sim}30{\mu}m$ and electro final stage polishing to observe lamellar orientation of same colony with EBSD (Electron Backscatter Diffraction Pattern). Through lamellar orientation as inter-lamellae or trans-lamellae, Cantilever beam was fabricated with Focused Ion Beam(FIB). The directional behavior of the lamellar structure was important property in single material, because of the effects of the different processing method and variations in properties according to lamellar orientation. In MEMS application, it is first necessary to have a reliable understanding of the manufacturing methods to be used to produce micro structure.