• Magazine of the Korea Concrete Institute
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• v.3 no.4
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• pp.79-88
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• 1991

In this study, fracture tests were carried out in order to investigate the fracture behavior of SFRC(Steel Fiber Peinforced Concrete) with initial cracks. The relationships between loading. strain, mld-span deflections and CMOD(Crack Mouth Opening Displacement) of the beams were observed under the three point loading system. The effect of the fiber content and the initial crack ratio on the concrete fracture behavior were studied and the fracture toughness, the critical energy release ratio and the fracture energy were also calcul ated from the test results. From the test results, it was known that when the fiber contents are between 0.5% and 1.0%, and 1.5% the average fracture energy of SFRC specimens is about 7~10 times. and about 15 times better than that of the plam concrete specimens respectively.ively.

• International Journal of Highway Engineering
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• v.8 no.1 s.27
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• pp.139-152
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• 2006

Many experimental and numerical approaches have been developed to evaluate paving materials and to predict pavement response and distress. Micromechanical simulation modeling is a technology that can reduce the number of physical tests required in material formulation and design and that can provide more details, e.g., the internal stress and strain state, and energy evolution and dissipation in simulated specimens with realistic microstructural features. A clustered distinct element modeling (DEM) approach was implemented In the two-dimensional particle flow software package (PFC-2D) to study the complex behavior observed in asphalt mixture fracturing. The relationship between continuous and discontinuous material properties was defined based on the potential energy approach. The theoretical relationship was validated with the uniform axial compression and cantilever beam model using two-dimensional plane strain and plane stress models. A bilinear cohesive displacement-softening model was implemented as an intrinsic interface and applied for both homogeneous and heterogeneous fracture modeling in order to simulate behavior in the fracture process zone and to simulate crack propagation. A disk-shaped compact tension test (DC(T)) with heterogeneous microstructure was simulated and compared with the experimental fracture test results to study Mode I fracture. The realistic arbitrary crack propagation including crack deflection, microcracking, crack face sliding, crack branching, and crack tip blunting could be represented in the fracture models. This micromechanical modeling approach represents the early developmental stages towards a 'virtual asphalt laboratory,' where simulations of laboratory tests and eventually field response and distress predictions can be made to enhance our understanding of pavement distress mechanisms, such its thermal fracture, reflective cracking, and fatigue crack growth.

• Journal of Biomedical Engineering Research
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• v.19 no.5
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• pp.433-441
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• 1998

This study was performed to evaluate the effects of surface flaw on the fracture of all-ceramic materials. A feldspathic porce lain of VMK68, a cashable ceramic of IPS-Empress, and an alumina-glass composite of In-Ceram were used. Specimens were prepared as 12$\times$3$\times$1mm in dimensions, and a Vickers-produced indentation crack was made at the center of the tensile surface. Test specimens were immersed in dlstilled water and In oil, which were broken under a crosshead speed of 0.05 mm/min by 3-point bend test at 37$^{\circ}C$. The characteristic patterns of Vickers indentation and fracture surfaces were examined by an optical microscope and a scanning electron microscope. The fracture surfaces of the VMK68 and the IPS-Empress showed a median crack pattern at the fracture origin and indicated a tendency to cleavage hackle. The fracture surface of the alumina-glass composite, In-Ceram, showed a Palmqvist crack pattern at the fracture origin and indicated a tendency of toughening by the frictional Interlocking between the microstructurally rough fracture surfaces.

• Korean Journal of Metals and Materials
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• v.47 no.9
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• pp.533-541
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• 2009

Materials used for a reactor pressure vessel(RPV) are required high strength and toughness, which determine the safety margin and life of a reactor. Ni-Mo-Cr low alloy steel shows better mechanical properties than existing RPV steels due to higher Ni and Cr contents compared to the existing RPV steels. The present study focuses on effects of Ni, Cr contents on the cleavage fracture toughness of Ni-Mo-Cr low alloy steels in the transition temperature region. The fracture toughness was characterized by a 3-point bend test of precracked Charpy V-notch(PCVN) specimens based on ASTM E1921-08. The test results indicated that the fracture toughness was considerably improved with an increase of Ni and Cr contents. Especially, control of Cr content was more effective in improving fracture toughness than manipulating Ni content, though Charpy impact toughness was changed more extensively by adjusting Ni content. These differences between changes in the fracture toughness and that in the impact toughness were derived from microstructural features, such as martensite lath size and carbide precipitation behavior.

• Geomechanics and Engineering
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• v.28 no.6
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• pp.613-624
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• 2022

A study of the evolution of overburden fractures under the solid-fluid coupling state was conducted based on the geological and mining characteristics of the coal seam depth, weak strata cementation, and high-intensity mining in the mining areas of West China. These mining characteristics are key to achieving water conservation during mining or establishing groundwater reservoirs in coal mines. Based on the engineering background of the Daliuta Coal Mine, a non-hydrophilic simulation material suitable for simulating the weakly cemented rock masses in this area was developed, and a physical simulation test was carried out using a water-sand gushing test system. The study explored the spatial distribution and dynamic evolution of the fractured zone in the mining overburden under the coupling of stress and seepage. The experimental results show that the mining overburden can be vertically divided into the overall migration zone, the fracture extension zone and the collapse zone; additionally, in the horizontal direction, the mining overburden can be divided into the primary fracture zone, periodic fracture zone, and stop-fracture zone. The scope of groundwater flow in the overburden gradually expands with the mining of coal seams. When a stable water inrush channel is formed, other areas no longer generate new channels, and the unstable water inrush channels gradually close. Finally, the primary fracture area becomes the main water inrush channel for coal mines. The numerical simulation results indicate that the overlying rock breaking above the middle of the mined-out area allows the formation of the water-conducting channel. The water body will flow into the fracture extension zone with the shortest path, resulting in the occurrence of water bursting accidents in the mining face. The experimental research results provide a theoretical basis for the implementation of water conservation mining or the establishment of groundwater reservoirs in western mining areas, and this theoretical basis has considerable application and promotion value.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 1999.06a
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• pp.201-206
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• 1999

The influence of surface preparation methods after plasma cutting on the quality of welding zone is investigated. For comparison. three types of welded specimens are prepared by machining(YM), plasma cutting with light regrinding(WPG) and without regrinding(WP), by using three kinds of materials, carbon steel(S45C), stainless steel(Type304) and aluminum alloy (6061-T6). Nondestructive examination, hardness test, microstructure examination, and fracture toughness test are performed. The results show that there is no appreciable reduction in hardness or fracture toughness in WP specimens. But a little difference in heat affected gone size is observed.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.116-122
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• 1989

MOR test and concentric ring test were performed to evaluate the failure probability of sin/hip Si3N4 under uniaxial and biaxial stress state, respectively. Their failure probabilities were analized with KARA program based on Weibull PIA model and Batdorf model with 5 criteria, and they were compared with experiments. PIA model is in best accordance with experiments in higher fracture strength regions, especially for Pf 0.3. But in lower fracture strength region, none of the models predicts the failure probabilities appropriately.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.27-30
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• 2003

In order to apply fracture detection we fabricated the CP-FRP using carbon-powder and analyzed conductive mechanism of it. The composites showed lower initial resistance as the carbon powder and amount of glass fiber(TEX) was used much more. When those are compared with each other that before and after bending test, the more cracks observed in matrix after bending test. We become to know that the conductivity of the composites depends on percolation structure of carbon powder.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.115-116
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• 2012

In this study, fitness and fatigue test were performed to estimate the coating effects of abutment screw for implant system after fatigue test. The purpose of this study was to investigate fatigue fracture phenomena of dental implant fixture used titanium nitride coated abutment screw under cyclic load.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.761-769
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• 1994

Actual load acting on rail surface in the track is the combined mode loading due to the contact rolling load of the wheels. To investigate the fracture behavior on rail steel under combined modes I and II, fracture tests were performed by using the test jigs and fracture specimen which were designed by Richard. The analysis results of experimental fracture data were compared with various fracture criteria that have been introduced for determination of the crack propagation direction and the critical stress of fracture of a crack submitted to a mixed mode loading. From the results, it was shown that the actual crack propagation direction of rail steel agree with the crack propagation directions predicted by maximum tangential stress criterion and strain energy density criterion, and that fracture criterion follows principal strain criterion.