• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.4
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• pp.3-9
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• 2013

Falling related injuries are categorized as the most serious and common medical problems experienced by the elderly. Hip joint fracture, one of the most serious consequences of falling in the elderly, occurs in only about 1% of falling. In this study, according to the loading conditions, the analysis is the behavior of the femur. The CT images using the commercial program "Mimics" the bones of three-dimensional CAD data generated, and we will analyze the results of finite element analysis. The boundary conditions on the basis of existing research has been simplified. In this paper, the whole femur was assumed to be isotropic linear elastic material. Predicted the behavior of the femur according to the loading condition, it can be help the development of high-precision artificial bones and joints can be treated with surgery and will be able to perform efficiently.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.577-580
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• 2004

Recently, DFRCCs (Ductile Fiber Reinforced Cementitious Composites), materials with remarkable ductility when compared to ordinary fiber-reinforced concrete (FRC), have been developed and studied actively in the US, Japan, and many European countries. The transformation of failure behavior from brittle to ductile is achieved by incorporating with fracture mechanics concept especially micro-mechanical models approach of cementitious composite materials in manufacturing ordinary fiber-reinforced composites. The purpose of this study is to accurately understand the shear behavior of DFRCC repaired RC beams. Using a four-point bending test, the shear strengths and shear stress-deflection relations of DFRCC repaired RC specimens are obtained. The results show that DFRCC can be effectively used for repairing materials for concrete structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.342-345
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• 2006

The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of HPFRCC(High performance fiber-reinforced cementitious composite). Acoustic emission(AE) method was used to evaluate the characteristics of fracture process and the micro-failure mechanism of HPFRCC. For these purposes, three kinds of fibers were used : PP(Polypropylene), PE(Polyethylene), SC(Steel cord). In this study, the AE characteristics of HPFRCC with different fiber type(PE.15, PP2.0, SC0.75+PE0.75) distributions under four-point-bending were studied. The result show that the AE technique is a valuable tool to study the failure mechanism of HPFRCC.

• Transactions of Materials Processing
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• v.15 no.8 s.89
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• pp.609-614
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• 2006

Micro-alloyed steels(MA steels) for cold forging was developed to replace the usual quenched and tempered steel. MA steels have several advantages over the conventional quenched and tempered carbon steels. First of all, energy consumption could be lowered due to the elimination of spherodizing annealing and quenching/tempering heat treatment. Also, bending during quenching could be avoided when MA steels are applied for manufacturing of long fastener parts. However, larger amount of load is exerted on the dies compared than in the case of conventional mild steels, which might lead to the earlier fracture of dies, when MA forging steels are applied in forging practice. Therefore, die lift could be a critical factor to determine whether HA forging steels could be widely applied in cold forging practice. In the present study, authors have investigated the forging characteristics of non-heat treated micro-alloyed steel by using a series of experimental and numerical analyses. Firstly, microstructural features and its effect on the deformation behavior have been studied. Numerical analysis has been done on the forging of guide rod pin to investigate for the optimization of forging process and die stress prediction.

• Transactions of Materials Processing
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• v.17 no.4
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• pp.240-248
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• 2008

The effect of alloying elements(Mn, S, Mo, B) on the high temperature deformation behavior of Fe-29%Ni-17%Co (Kovar) alloy were investigated. And the effect of high temperature oxidation on the hot ductility was also studied. The hot ductility of Kovar alloy was drastically increased with the addition of Mn and lowering of S content. It has been found that the brittle intergranular fracture at high temperature cracking is closely associated with the FeS sulfide along the grain boundary. When Mn was added, the type of sulfide was changed to MnS from FeS and ductile intergranular fracture and transgranular fracture were promoted. The formation of oxide layer was found to have minimized the hot ductility of the Kovar alloy significantly. Grain boundary micro-cracks in the internal oxide region were noted following deformation due to high temperature, one of which acting as a notch that caused the poor hot workability of the oxidized specimen. The addition of Mo to the Kovar alloy could also retard the decrease in the hot ductility of the oxidized specimen through the prevention of notching due to internal oxidation. Hot ductility was remarkably improved by the addition of Boron. The improvement of hot ductility results from the grain boundary migration mainly due to the dynamic recrystallization at lower temperature range ($900{\sim}1000^{\circ}C$).

• Economic and Environmental Geology
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• v.32 no.1
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• pp.93-100
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• 1999

In rock, there are many microsopic structures which influence the mechnical behavior of rock. Many microstructures interact with each other, and furthermore, material constants vary discontinuously within rock, as most rocks are composed of several minerals. Taking into account this feature, it may be possible to contemplate a microstructure of rock as a unit cell by which the rock is constituted periodically. If this idealization is acceptable, the homogenization method can be applied. In this research, various microcracks on rock specimens were observed through a stereoscopic microscope under uniaxial compression. On the other hand, local stress distribution in the periodic-micro structure was calculated by the homogenization method. Then it is shown that there is a possibility to establish a relation between the behavior of microcrack and macroscopic load quantitatively by the linear fracture mechanics.

• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.581-596
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• 2016

A comprehensive review on sliding and solid particle erosion wear characteristics of silicon carbide (SiC) ceramics and SiC composites is provided. Sliding or erosion wear behavior of ceramics is dependent on various material characteristics as well as test parameters. Effects of microstructural and mechanical properties of SiC ceramics are particularly focused to understand tribological performance of SiC ceramics. Results obtained between varieties of pairs of SiC ceramics indicate complexity in understanding dominant mechanisms of material removal. Wear mechanisms during sliding are mainly divided in two groups as mechanical and tribochemical. In solid particle erosion conditions, wear mechanisms of SiC ceramics are explained by elastic-plastic deformation controlled micro-fracture on the surface followed by radial-lateral crack propagation beneath the plastic zone.

• Advances in concrete construction
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• v.3 no.1
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• pp.15-37
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• 2015

Ongoing efforts for improved fracture toughness of engineered cementitious materials address the inherent brittleness of the binding matrix at several different levels of the material's geometric scale through the addition of various types of reinforcing fibers. Crack control is required for crack widths that cover the entire range of the grain size spectrum of the material, and this dictates the requirement of hybrid mixes combining fibers of different size (nano, micro, macro). Use of Carbon Nano-Tubes (CNT) and Carbon Nano-Fibers (CNFs) as additives is meant to extend the crack-control function down to the nanoscale where cracking is believed to initiate. In this paper the implications of enhanced toughness thus attained at the material nanostructure are explored, with reference to the global smeared constitutive properties of the material, through consistent interpretation of the reported experimental evidence regarding the behavior of engineered cementitious products to direct and indirect tension.

• Structural Engineering and Mechanics
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• v.84 no.2
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• pp.253-268
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• 2022

Using non-destructive Acoustic Emission (AE) and optical Digital Image Correlation (DIC) methods, the moment-curvature behavior of steel and GFRP bars reinforced concrete beams under flexure was explored in this study. In the tension zone, laboratory studies were carried out on steel-RC and GFRP-RC beams with varying percentages of longitudinal reinforcement ratios of 0.33 %, 0.52%, and 1.11%. The distinct mechanism of cracking initiation and fracture progression of failure in steel-RC and GFRP-RC beams were effectively correlated and picked up using AE waveform characteristics of the number of AE hits and their amplitudes, AE energy as well as average frequency and duration. AE XY event plots and longitudinal strain profiles using DIC gives an online and real-time visual display of progressive AE activity and strains respectively to efficaciously depict the crack evolution and their advancement in steel-RC and GFRP-RC beams. They display a close matching with the micro and macro-cracks visually observed in the actual beams at various stages of loading.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.52-59
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• 2003

Tests of concrete CLWL-DCB specimens had been conducted with displacement-controlled dynamic loading. The crack velocities for 381mm crack extension were 0.80 mm/sec ~ 215m/sec. The external work and the kinetic and strain energies were derived from the measured external load and load-point displacement. The fracture resistance of a running crack was calculated from the fitted curves of the fracture energy required for the tests. The standard error of the fracture energy was less than 3.2%. The increasing rate of the fracture resistance for 28 mm initial crack extension or micro-cracking was relatively small, and then the slope of the fracture resistance increased to the maximum value at 90∼145 mm crack extension depending on crack velocity. The maximum fracture resistance remained for 185 mm crack extension, and then the faster crack velocity showed the faster decreasing rate of the maximum fracture resistance. The maximum fracture resistance increased proportionally to the logarithm of the crack velocity from 142 N/m to 217 N/m when the crack velocity was faster than 0.273 m/sec. The maximum fracture resistance of the fastest tests was similar to the average fracture energy density of 215 N/m. To measure the fracture resistance of concrete, the stable crack extension should be larger than 90∼145 mm depending on crack velocity.