• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.876-888
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• 2005

Tensile properties and fracture toughness of monolithic aluminum, fiber reinforced plastics and glass fiber/aluminum hybrid laminates under tensile loads have been investigated using plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed different characteristic behaviors according to the Al kind, fiber orientation and composition ratio. Fracture, toughness of A-GFML-UD which was determined by the evaluation of $K_{IC}$ and $G_{IC}$ based on critical load was similar to that of GFRP-UD and was much higher than monolithic Al. Therefore, A-GFML-UD presented superior fracture toughness as well as prominent damage tolerance in comparison to its constituent Al. By separating Al sheet from GFMLs after the test, optical microscope observation of fracture zone of GFRP layer in the vicinity of crack tip revealed that crack advance of GFMLs depended on the orientation of fiber layer as well as Al/fiber composition ratio.

• Composites Research
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• v.14 no.3
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• pp.51-56
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• 2001

It is known that the elastic modulus, maximum stress, and maximum strain of fiber-reinforced polymer composites are affected by high pressure. Fracture behavior is also known to be affected by high pressure. In this work, the pressure effect on the compressive fracture toughness of thick quasi-isotropic composites was investigated. Dog-bone type specimens of stacking sequence, [0$^{\circ}$/$\pm$45$^{\circ}$/90$^{\circ}$]$_{11s}$ were used. Compressive fracture tests were conducted under four pressure levels. The pressure levels applied were 0.1 MPa, 100 MPa, 200 MPa, and 300 MPa. Fracture toughness for each pressure level was determined from the compliance method. The results show that the compressive fracture toughness increases with increasing pressure. Specifically, fracture toughness increases 44% as the pressure increases from 0.1 MPa to 300 MPa.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.187-187
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• 1997

Silicon nitride is the most excellent materials among structural ceramics. It has been reported that fracture toughness was improved with adding second phase particles, whisker, fiber etc. However, containing of second phase particles enhanced fracture toughness, however flexural strength was degraded. As adding nanosize SiC particles into silicon nitride, the physical properties of fluxural strength, fracture toughness, the modulus of elasticity. In this study, 2wt% $Al_2$O$_3$ and 4 wt% $Y_2$O$_3$ were added into UBE E-10 and 0, 10, 20, 30, 40, 50 vol% nano-SiC powder (Sumitomo T1 powder) were added, respectively. It is hot pressed at 185$0^{\circ}C$ for 1 hour. Most of structural ceramics for engineering application are wear resistance. In this study, wear behaviors (in water) of silicon nitride with varying the amount of nano-size silicon carbide were investigated, and was compared to physical properties. Simultaneously wear mechanism will be found out.

• Journal of the Korean Ceramic Society
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• v.43 no.8 s.291
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• pp.469-471
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• 2006

The effects of $Cr_2O_3$ on the microstructural evolution and mechanical properties of $Al_2O_3$ polycrystalline were investigated. The microstructure of $Al_2O_3-Cr_2O_3$ composites (ruby) was carefully controlled in order to obtain dense and fine-grained ceramics, thereby improving their properties and reliability with respect to numerous applications related to semiconductor bonding technology. Ruby composites were produced by Ceramic Injection Molding (CIM) technology. Room temperature strength, hardness, Young's modulus and toughness were determined, as well as surface strengthening induced by thermal treatment and production of a fine-grained homogenous microstructure.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.61-65
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• 2001

The fracture toughness of ceramics can be measure by such various methods as DT (double torsion), CN (chevron notch) etc. But, the application of these methods to the engineering ceramics is very difficult because of its very high hardness. So, IF (indentation fracture) method is generally used for the evaluation of fracture toughness of ceramics. The Median crack induced by the sharp Vickers indenter was compared with the detected AE (acoustic emission) signal. On the silicon nitride ceramics, the AE test results agree fairly well with the median crack occurance and growth process. But, on the alumina, very many complicated crack signals were detected besides median crack. It can be considered that the IF methods must be used in limited engineering ceramics materials.

• Earthquakes and Structures
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• v.10 no.4
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• pp.769-788
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• 2016

The present study aimed at investigating the effect of a special plaster on the out-of-plane behavior of masonry walls. A reference specimen, plastered with conventional plaster, and a specimen plastered with a special plastered were tested under reversed cyclic lateral loading. The specimens were identical in dimensions and material properties. The special plaster contained an additive, which increased the adherence strength of the plaster to the wall. The amount of the additive in the mortar was adjusted based on the preliminary material tests. The influence of the plaster on the wall behavior was evaluated according to the initial cracking load, type of failure, energy absorption capacity (modulus of toughness), and crack pattern of the wall. Despite having limited contribution to the ductility, the special plaster increased the ultimate load capacity of the wall about 25%. The failure mode of the wall with special plaster resembled the plastic failure mechanism of a reinforced concrete slab in the formation of yielding lines along the wall. The deflection at failure and the modulus of toughness of the wall with special plaster were measured to be in order of 60% and 75% of the corresponding values of the reference wall.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.5
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• pp.425-434
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• 1984

The concept of intermittent interlaminar bonding is investigated as a means of improving the fracture toughness of cross-ply Gr/Ep composites without significant loss of tensile strength and modulus. The concept of linear elastic fracture mechanics(LEFM)is used to study the effects of strong bonded area and bonding composites. The experimental results indicate that the fracture toughness and notch strength of intermittent interlaminar bonded composities are improved and the tensile strength only decreased by 3-8% in comparison to those of the fully bonded composites. Damage zones around the crack tip are detected by the modified X-Ray non-destructive testing technique and the fractography. The improvement of toughness is explained based on the damage zones. The mechanisms of damage zone are shown to be caused by subcrack along the fiber on the 0.deg. ply, matrix cracking along the fiber on the 90.deg. ply, interlaminar delamination, and ply pull-out of the 0.deg. ply.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.11
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• pp.2860-2870
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• 1994

When crack are detected in aged turbine rotors of power plants, information on fracture resistance of the aged material at operating temperature is needed for determination of critical loading condition and residual life of the turbine. In this study, fracture toughness (J$_lc$) and tearing modulus(T$_mat$) of virgin and thermally degraded 1Cr-1Mo-0.25V steel, which is one of the most widely used rotor steels, were measured at 538.deg. C according to ASTM E813 and ASTM E1152, respectively. Five kinds of specimen with different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C.$ It was observed that J$_lc$ and T$_mat$ value decreased as the degradation level increased. Analysis of microstructures using a scanning electron microscope showed that the decrement of J$_lc$ is related to segregation of impurities at grain boundaries. It was also verified that the DC electric potential drop method is accurate and reliable for crack length monitoring at elevated temperature.

• Structural Engineering and Mechanics
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• v.46 no.2
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• pp.295-322
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• 2013

Steel fiber reinforced self-compacting concrete (SFRSCC) is a relatively new composite material which congregates the benefits of self-compacting concrete (SCC) technology with the profits derived from the fiber addition to a brittle cementitious matrix. Steel fibers improve many of the properties of SCC elements including tensile strength, toughness, energy absorption capacity and fracture toughness. Modification in the mix design of SCC may have a significant influence on the SFRSCC mechanical properties. Therefore, it is vital to investigate whether all of the assumed hypotheses for steel fiber reinforced concrete (SFRC) are also valid for SFRSCC structures. Although available research regarding the influence of steel fibers on the properties of SFRSCC is limited, this paper investigates material's mechanical properties. The present study includes: a) evaluation and comparison of the current analytical models used for estimating the mechanical properties of SFRSCC and SFRC, b) proposing new relationships for SFRSCC mixtures mechanical properties. The investigated mechanical properties are based on the available experimental results and include: compressive strength, modulus of elasticity, strain at peak compressive strength, tensile strength, and compressive and tensile stress-strain curves.

• Advances in concrete construction
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• v.2 no.2
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• pp.145-162
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• 2014

In this study, the fracture toughness $K_{IC}$ of high performance concrete (HPC) was determined by conducting three-point bending tests on eighty notched HPC beams of $500mm{\times}100mm{\times}100mm$ at high temperatures up to $450^{\circ}C$ (hot) and in cooled-down states (cold). When the concrete beams exposed to high temperatures for 16 hours, both thermal and hygric equilibriums were generally achieved. $K_{IC}$ for the hot concrete sustained a monotonic decrease tendency with the increasing temperature, with a sudden drop at $105^{\circ}C$. For the cold concrete, $K_{IC}$ sustained a two-stage decrease trend, dropping slowly with the heating temperature up to $150^{\circ}C$ and rapidly thereafter. The fracture energy-based fracture toughness $K_{IC}$' was found to follow similar decrease trends with the heating temperature. The weight loss, the fracture energy and the modulus of rapture were also evaluated.