• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.5
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• pp.603-613
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• 2024

This study evaluated the mechanical properties of high-tension performance biochar concrete, focusing on the effects of varying biochar cement replacement ratios (0 %, 1 %, 2 %, 3 %, 4 %, and 5 %). Mechanical properties, including compressive strength, tensile strength, and flexural strength, were tested. The results showed a general decrease in compressive strength with increasing biochar replacement, with significant reductions at 1 % to 3 % levels. PVA fiber reinforcement improved long-term compressive strength, particularly at higher biochar levels. Tensile and flexural strength also showed initial reductions with low biochar levels but improved at higher replacement levels. PVA fibers consistently enhanced tensile and flexural strength. SEM images confirmed the integration of biochar and PVA fibers into the cement matrix, enhancing microstructural density and crack resistance.

• Composites Research
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• v.28 no.6
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• pp.366-371
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• 2015

In order to improve the mechanical properties of tungsten at room and elevated temperature, hafnium carbide (HfC) reinforced tungsten matrix composites were prepared using the spark plasma sintering technique. The effect of HfC content on the compressive strength and flexural strength of the tungsten composites was investigated. Mechanical properties of the composites were also measured at elevated temperatures and their trends, with varying reinforcement volume fraction, were studied. The effect of reinforcement fraction on the thermal properties of the composites was investigated. The thermal conductivity and diffusivity of the composites decreased with increasing temperature and reinforcement volume fraction. An inherently low thermal conductivity of the reinforcement as well as interfacial losses was responsible for lower values of thermal conductivity of the composites. Values of coefficient of thermal expansion of the composites were observed to increase with HfC volume fraction.

• Korean Journal of Metals and Materials
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• v.47 no.1
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• pp.50-58
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• 2009

In this study, alumina matrix composites reinforced with carbon nanotubes (CNTs) were fabricated by ultrasonic dispersion, ball milling, mixing, compaction, and sintering processes, and their relative density, electrical resistance, hardness, flexure strength, and fracture toughness were evaluated. 0~3 vol.% of CNTs were relatively homogeneously dispersed in the composites in spite of the existence of some pores. The three-point bending test results indicated that the flexure strength increased with increasing volume fraction of CNTs, and reached the maximum when the CNT fraction was 1.5 vol.%. The fracture toughness increased as the CNT fraction increased, and the fracture toughness of the composite containing 3 vol.% of CNTs was higher by 40% than that of the monolithic alumina. According to observation of the crack propagation path after the indentation fracture test, a new toughening mechanism of grain interface bridging-induced CNT bridging was suggested to explain the improvement of fracture toughness in the alumina matrix composites reinforced with CNTs.

• Advanced Composite Materials
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• v.18 no.3
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• pp.221-232
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• 2009

The allylamine plasma treatment is used to modify the surface properties of vapor grown carbon fibers (VGCF). It is to improve the interfacial bonding between the VGCF and epoxy matrix. The allylamine plasma process was performed by batch process in a vacuum chamber, using gas injection followed by plasma discharge for the durations of 20, 40 and 60 min. The interdependence of mechanical properties on the VGCF contents, treatment time and interfacial bonding between VGCF/ep was investigated. The interfacial bonding between VGCF and epoxy matrix was observed by scanning electron microscopy (SEM) micrographs of nanocomposites fracture surfaces. The changes in the mechanical properties of VGCF/ep, such as the tensile modulus and strength were discussed. The mechanical properties of allylamine plasma treated (AAPT) VGCF/ep were compared with those of raw VGCF/ep. The tensile strength and modulus of allyamine plasma treated VGCF40 (40 min treatment)/ep demonstrated a higher value than those of other samples. The mechanical properties were increased with the allyamine plasma treatment due to the improved adhesion at VGCF/ep interface. The modification of the carbon nanofibers surface was observed by transmission electron microscopy (TEM). SEM micrographs showed an excellent dispersion of VGCF in epoxy matrix by ultrasonic method.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.83-91
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• 1996

Monolithic AlN and AlN-W composites were fabricated by pressure-less sintering at 190$0^{\circ}C$ under nitrogen atmosphere and the influences of tungsten phase on the microstructure and mechanical properties were investi-gated. In the fabrication of sintered specimen no additive was used. And monolithic AlN showed substantial grain growth and low relative density. AlN-W composites were fully densified and grain growths of matrix were inhibited. The densification behavior of composites were inferred to be achieved through the liquid phase sintering process such as particle-rearrangement and solutino-reprecipitation. Also the oxid phases which is expected to form liquid phases duringsintering process were detected by XRD analysis. As the tungsten volume content increases fracture strength was decreased and fracture toughness was increased. It was suppo-sed that the strength decrease of composites with tungsten content was due to existence of interface phases. The subcritical crack growth behavior was observed from the stress-strain curve of composites. The effect of the secondary phase and interface phases on toughness in crease were studied through observation of crack propagation path and the influence of residual stress on crack propagation was investigated by X-ray residual stress measurement. In the result of residual stress measurement the compressive stress of matrix in composi-test was increased with tungsten volume content and the compressive stress distribution of matrix must have contributed to the inhibition of crack propagation.

• Korean Journal of Metals and Materials
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• v.48 no.7
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• pp.683-689
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• 2010

In this study, FeAl based intermetallic matrix composites reinforced with in-situ synthesized TiC particles were fabricated by an in-situ liquid mixing process. The microstructures, mechanical properties and fracture behaviors of the in-situ liquid mixing processed composite were investigated and compared with the vacuum suction casting processed composite. The results showed that the in-situ formed TiC particles exhibited fine and uniform dispersion in the liquid mixing processed composite, while significant grain boundary clustering and coarsening of TiC particles were obtained by the vacuum suction process. It was also shown in both types of composites that the hardness and bending strength were increased with the increase of the TiC volume fractions. Through the study of fractography in the bending test, it was considered that the TiC particles prohibited brittle intergranular fracture of FeAl intermetallic matrix by crack deflections. Because of the uniformly distributed fine TiC particles, the bending strength of the liquid mixing processed composite was superior to that of the casting processed composite.

• Corrosion Science and Technology
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• v.20 no.5
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• pp.295-307
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• 2021

Effects of ε-carbide (Fe_2.4C) on corrosion and hydrogen diffusion behaviors of ultra-strong steel sheets for automotive application were investigated using a number of experimental and analytical methods. Results of this study showed that the type of iron carbide precipitated during tempering treatments conducted at below A₁ temperatures had a significant influence on corrosion kinetics. Compared to a steel sample with cementite (Fe₃C), a steel sample with ε-carbide (Fe_2.4C) showed higher corrosion resistance during a long-term exposure to a neutral aqueous solution. In addition, the diffusion kinetics of hydrogen atoms formed by electrochemical corrosion reactions in the steel matrix with ε-carbide were slower than the steel matrix with cementite because of a comparatively higher binding energy of hydrogen with ε-carbide. These results suggest that designing steels with fine ε-carbide distributed uniformly throughout the matrix can be an effective technical strategy to ensure high resistance to hydrogen embrittlement induced by aqueous corrosion.

• Archives of Metallurgy and Materials
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• v.63 no.3
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• pp.1485-1488
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• 2018

The effect of additives on the densification behavior and mechanical properties of pure and additive (Zr, B and Mg)-added silica ceramics were investigated for their application to the matrix phase of a silica fiber reinforced silica (SiO₂/SiO_2f) composite. The additives affected the rate of densification and crystallization (or transformation) of the amorphous silica. Among the compositions, pure silica ceramics sintered at 900℃ for 1 h showed the maximum flexural strength. Based on the results, SiO₂/SiO_2f was fabricated by a repeated vacuum-assisted infiltration method followed by the heat treatment at 900℃ for 1 h. The relative density of the composite was 78.2% with a flexural strength of 22.4 MPa. Fractography revealed that the composite was damaged by strong bonding at the fiber/matrix interface and the fracture of fiber.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 2000.06a
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• pp.233-242
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• 2000

Cordierite/ZrO$_2$ composites with 5 to 25wt% ZrO$_2$ were fabricated by prssureless sintering, and their densification behavior, fracture strength, fracture toughness, microstructure and thermal expansion behavior were studied. The ZrO$_2$ addition into cordierite matrix affects the densification behavior and mechanical properties of the composites. By dispersing 25wt% ZrO$_2$, densified cordierite/ZrO$_2$ composite with a relative density of 98.5% was obtained at optimum sintering condition of 144$0^{\circ}C$/2H. Both fracture strength and toughness were increased from 140 to 290MPa and from 1.6 to 3.5 MPam$\frac{1}{2}$, respectively, by dispersing 25wt% ZrO$_2$ into the cordierite matrix. ZrO$_2$ particles were homogenously dispersed into cordierite matrix, which intragranular particles were fine(<100nm) and intergranular particles were coarse. The toughening mechanisms in the present composites were mainly attributed to martensitic transformation toughening. Then, the addition of ZrO$_2$ is likely to have little deleterious effect upon thermal expansion coefficient of cordierite.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.2
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• pp.72-78
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• 2002

Thermomechanical behavior and mechanical properties of A16061 matrix composite with shape memory alloy(SMA) fiber are studied by using fnite element analysis(FEA). The smartness of the SMA is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when healed after being prestrained. In this paper, an analytical model is assumed two dimentional axisymetric model of one fiber and around the matrix. To evaluate the strength of composite usig FEM, the concept of smart composite was simulated on computer. The Shape memory effect(SME) simulation is very difficult using FEM because of the nonlinear analysis and the elastic plastic analysis. Thus, in this paper, the FEA was carried out at two critical temperature conditions; room temperature and high temperature(363K). The analysis is compare the finite element analysis result with the test result for the analysis validity.