• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.745-752
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• 1994

A polymer reinforced grouts using ordinary portland cement mortar and water soluble polymer{polyvinyl alcohol(PVA), styrene-butadiene rubbre(SBR), etylene-vinyl acetate copolymer(EVA)} were made. The mechanical properties of the hardened specimens were investigated through the observation of the microstructure and application of fracture mechanics. When the PVA, SBR and EVA was added with 1.5 wt% to the grouts, the compressive strength were about 54 MPa, 63 MPa and 68 MPa respectively, and the flexural strength was about 11 MPa, 12.8 MPa, and 13.6 MPa respectively, and Young's modulus was about 3.8 GPa, 4.4 GPa and 4.6 GPa respectively, and critical stress intensity was about 0.73 MNm-1.5, 0.85 MNm-1.5 and 0.9 MNm-1.5 respectively. It can be considered that the strength improvement of polymer mortar grouts may be due to the removal of macropores and the increase of various fracture toughness effects, such as grain bridging, frictional interlocking and polymer bridging.

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.139-147
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• 1993

Two sheets of high strength cement paste using ordinary Portland cement and water soluble polymer (polyacrylamide) were made by kneading with a twin roll mill. A carbon fiber layer out between two sheet of the cement paste, and then carbon fiber reinforced high strength cement composites were prepared by pressing them. The mechanical properties of the composites were investigated through the observation of the microstructure and the application of fracture mechanics. When the carbon fiber was added with 0.2 and 0.3wt% to the composites the flexural strength and Young's modulus were about 110∼116MPa and 74∼77GPa respectively, and critical stress intensity was about 3.14MPam1/2. It can be considered that the strength improvement of high strength cement fiber composites may be due to the removal of macropores and the increase of various fracture toughness effects; grain bridging, frictional interlocking, polymer fibril bridging and fiber bridging.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.491-498
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• 1994

A fiber reinforced grouts were made using ordinary cement mortar and high effective water reducing agent (naphthalene sulfonate) were made by addition polypropylene fiber and carbon fiber. The physical properties of the grouts were investigated through the observation of the microstructure and the application of fracture mechanics. When the polypropylene fiber and carbon fiber were added respectively with 0.03 wt% to the grouts the compressive strength, flexural strength and Young's modulus were about 60∼63 MPa, 12.2∼12.4 MPa, 4.2∼4.8 GPa and 63∼68 MPa, 12.2∼12.6 MPa, 4.8∼5.1 GPa, and critical stress intensity were about 0.77∼0.82 MNm-1.5, and 0.80∼0.87 MNm-1.5 respectively, It can be considered that the strength improvement of fiber reinforced grouts (FRG) may be due to the removal of macropores and the increase of various fracture toughness, polymer fibril bridging and fiber bridging.

• The Korean Journal of Ceramics
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• v.3 no.3
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• pp.199-207
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• 1997

$Al_2O_3$/SiC particulate composites were fabircated by pressureless sintering. The dispersed phase was SiC of which the content was varied from 1.0 to 10 vol%. Three SiC powders having different median diameters from 0.28 $\mu\textrm{m}$ to 1.9 $\mu\textrm{m}$ were used. The microstructure became finer and more uniform as the SiC content increased except the 10 vol% specimens, which were sintered at a higher temperature. Under the same sintering condition, densification as well as grain growth was retarded more severly when the SiC content was higher or the SiC particle size was smaller. The highest flexural strength obtained at 5.0 vol% SiC regardless of the SiC particle size seemed to be owing to the finer and more uniform microstructures of the specimens. Annealing of the specimens at $1300^{\circ}C$ improved the strength in general and this annealing effect was good for the specimens containing as low as 1.0 vol% of SiC. Fracture toughness did not change appreciably with the SiC content but, for the composites containing 10 vol% SiC, a significantly higher toughness was obtained with the specimen containing 1.9$\mu\textrm{m}$ SiC particles.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.25-37
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• 1993

This paper describes the use of the J-integral, a one parameter of the non-linear fracture mechanics(NLFM), as a means to measure toughness of steel fiber reinforced concrete. This parameter can be conveniently evaluated from experimentally determined load-deflection curves from flexural tests when a maximum-load failure criterion is employed. And, for high strength concrete which was reinforced steel fiber, with two different fiber length in the form of notched beams, were tested under 3-point bending, and $J_{IC}$, as well as the linear elastic fracture mechanics(LEFM) parameters $K_{IC}$ and $G_{IC}$ were evaluated. The results suggest that $J_{IC}$ is a promising fracture criterion for all of these. while $K_{IC}$(or $G_{IC}$) almost certainly are not. Also it was found that a fiber addition of less than 0.5% did not improve the fracture toughness of the high strength concrete. However, at more than 1.0% in fiber contents, $J_{IC}$ showed significant increases. reflecting the changed character of the concrete; $K_{IC}$ and $G_{IC}$ did not.

• Korean Journal of Materials Research
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• v.10 no.12
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• pp.838-844
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• 2000

For the fabrication of titanium diboride($TiB_2$)- based cermet as applications of cutting tools and wear resistant materials, a binder metal with good mechanical properties and sinterability is essential. In this study, SUS316L was chosen for the binder metal to obtain a new $TiB_2$ cermet with superior hardness and toughness.$TiB_2$-SUS316L cermets were densified to relative density of more than 99% by pressureless sintering at temperature above $1650^{\circ}C$ The flexural strength was up to 1290MPa at 10vo1%SUS316L cermet in spite of the formation of $Fe_2$B phase during the sintering. The fracture toughness was obtained up to $6MPam^{1/2}$ with Victors hardness over 18Gpa. These hardness and fracture toughness combinations are better than those of conventional cermet. The high temperature strength remarkably decreased by the plastic deformations of SUS316L binder phase at nearby $800^{\circ}C$ .

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.1
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• pp.58-65
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• 2007

Mixed mode interlaminar fracture behaviors of carbon fabric/epoxy composites were investigated through MMF (Mixed Mode Flexural) test by varying mixed mode ratio ranging from 20% to 90%. Mixed mode interlaminar fracture criteria based on NL point and 5% offset point were also suggested in order to predict mixed mode interlaminar fracture behaviors. Fracture surfaces and crack propagating behaviors were examined through a travelling scope and a scanning electron microscope. According to the results, mixed mode interlaminar fracture behaviors can be predicted by mixed mode interlaminar fracture criterion with m=1.5 and n=0.5 on the basis of NL point or mixed mode interlaminar fracture criterion with m=2 and n=3 on the basis of 5% offset point. Fracture surfaces and crack propagating behaviors are sensitive to mixed mode ratios. MMF test can be successfully applicable in evaluating mixed mode interlaminar fracture toughness of carbon fabric/epoxy composites.

• The Journal of Korean Academy of Prosthodontics
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• v.60 no.1
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• pp.9-18
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• 2022

In vitro studies are essential to predict the clinical performance of ceramic widely used as restorative materials. Traditional experiments such as fracture toughness and flexural strength have been used to evaluate the properties of brittle ceramics. However, these experiments have a limitation that the load conditions, failure patterns, and load values at which failure occurs are not similar to human occlusal force ranges or clinical failures. On the other hand, the edge chipping test (ECT), which was recently introduced to study chipping fracture of ceramics, has similar failure patterns to clinical trials. In addition, the failure loads from ECT were similar to human occlusal force. ECT can be usefully used in the study of ceramic properties. In this literature review, a more clinically meaningful experimental study of ceramics by examining the meaning and limitations of traditional ceramic failure tests and comparing them with ECT.

• Textile Coloration and Finishing
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• v.30 no.2
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• pp.98-106
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• 2018

In this study, graphene oxide(GO) was synthesized by using Hummer's method. Then, GO was used as a additive for epoxy resin nanocomposites that were prepared by mixing Tetraglycidyl diamino diphenyl methane(TGDDM) and hardner(MDEA+M-MIPA). Thermal and mechanical properties of epoxy resin nanocomposites were confirmed by analytical methods such as TG-DTA, DMA, fracture toughness, tensile strength, and flexural strength. The fracture surfaces of epoxy resin nanocomposites with different content of the GO were observed by a Scanning Electron Microscope(SEM). The mechanism for mechanical properties of epoxy resin nanocomposites was analyzed by modeling of nanocomposites with different GO weight. Due to the GO, both the heat resistance and the glass transition temperature of the epoxy resin nanocomposites were improved. Interestingly, when 0.1wt.% of GO was added to the epoxy resin/hardner mixture, the properties of mechanical increased compared with the neat epoxy resin. This results were caused by an aggregation between the GO.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.172-176
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• 1998

Epoxy adduct carboxyl terminated butadiene acrylonitrile(CTBN) was prepared by blending of CTBN and epoxy resin. CTBN/PU/epoxy was prepared from polyurethane(PU), epoxy resin, and CTBN. The CTBN/PU/epoxy using 5 wt% of CTBN content showed shifting damping peak as PU content increased. It suggested that CTBN/PU/epoxy had good compatibility for all composition at 5 wt% of CTBN content. But miscibility of CTBN/PU/epoxy decreased with the increase of the CTBN content. PU content for maximum flexural properties of CTBN/PU/epoxy was 10 wt%, but decreased with the increase of the PU content. The fracture toughness of CTBN/epoxy was improved by addition of the PU. Fracture surfaces of CTBN/PU/epoxy showed the shear deformation and generation of stress whitening which is associated with the cavitation. Cavitation in the CTBN and shear defomation in the PU modified epoxy matrix are the toughening mechanisms for CTBN/PU/epoxy.