• Computers and Concrete
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• v.17 no.4
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• pp.553-566
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• 2016

Fracture energy is one of the key parameters reveal cracking resistance and fracture toughness of concrete. The main purpose of this study is to determine fracture behavior, mechanical properties and microstructural analysis of high strength basalt fiber reinforced concrete (HSFRC). For this purpose, three-point bending tests were performed on notched beams produced using HSFRCs with 12 mm and 24mm fiber length and 1, 2 and $3kg/m^3$ fiber content in order to determine the value of fracture energy. Fracture energies of the notched beam specimens were calculated by analyzing load versus crack mouth opining displacement curves by the help of RILEM proposal. The results show that the effects of basalt fiber content and fiber length on fracture energy are very significant. The splitting tensile and flexural strength of HSFRC increased with increasing fiber content whereas a slight drop in flexural strength was observed for the mixture with 24mm fiber length and $3kg/m^3$ fiber content. On the other hand, there was no significant effect of fiber addition on the compressive strength and modulus of elasticity of the mixtures. In addition, microstructural analysis of the three components; cement paste, aggregate and basalt fiber were performed based on the Scanning Electron Microscopy and Energy-Dispersive X-ray Spectroscopy examinations.

• Computers and Concrete
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• v.5 no.4
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• pp.343-358
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• 2008

This article focuses on concrete structures submitted to impact loading and is aimed at predicting local damage in the vicinity of an impact zone as well as the global response of the structure. The Discrete Element Method (DEM) seems particularly well suited in this context for modeling fractures. An identification process of DEM material parameters from macroscopic data (Young's modulus, compressive and tensile strength, fracture energy, etc.) will first be presented for the purpose of enhancing reproducibility and reliability of the simulation results with DE samples of various sizes. The modeling of a large structure by means of DEM may lead to prohibitive computation times. A refined discretization becomes required in the vicinity of the impact, while the structure may be modeled using a coarse FE mesh further from the impact area, where the material behaves elastically. A coupled discrete-finite element approach is thus proposed: the impact zone is modeled by means of DE and elastic FE are used on the rest of the structure. The proposed approach is then applied to a rock impact on a concrete slab in order to validate the coupled method and compare computation times.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.85-95
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• 2018

Water affects the mechanical properties of coal and stress wave propagation. To comprehensively investigate the effect of water content on the properties of coal, laboratory tests including X-Ray Diffraction (XRD) analysis, P-wave test, S-wave test, static and dynamic compression test with different water contents were conducted. The compressive strength, elastic modulus and failure strain and their mechanism of coal specimen under coupled static-dynamic load with the increased water content were observed. Meanwhile, energy transmission and dissipation characteristics of a stress wave in coal specimens with different water contents under dynamic load and its relation with the failure features, such as fragmentation and fractal dimension, of coal was analyzed. Furthermore, the dynamic interpretation of water infusion to prevent coal burst based on water infusion model of coal seam roadway was provided.

• Journal of the Korean Society of Safety
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• v.30 no.5
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• pp.67-73
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• 2015

In this paper, the simple truss model was modified to predict the punching shear strength of long-span prestressed concrete (PSC) deck slabs under wheel load including the effects of transverse prestressing and long span length between girders. The strength of the compressive zone arounding punching cone was evaluated by the stiffness of inclined strut which was modified by considering aging effective modulus. The stiffness of springs which control lateral displacement of the roller supports consists of the steel reinforcement and prestressing which passed through the punching cone. Initial angle of struts was determined by the experimental observation to compensate for uncertainties in the complexities of the punching shear. The validity of computed punching shear strength by modified simple truss model was shown by comparing with experimental results and the experimental results were also compared with existing punching shear equations to determine level of predictability. The modified simple truss model appeared to better predict the punching shear strength of PSC deck slabs than other available equations. The punching shear strength, which was determined by snap-through critical load of modified simple truss model, can be used effectively to examine punching shear strength of long span PSC deck slabs.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.53.2-53.2
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• 2011

Ti metal has superior mechanical properties along with biocompatibility, but it still has the problem of bio-inertness thus forming weaker bond in bone/implant interface and long term clinical performance as orthopaedic and dental devices are restricted for stress shielding effect. On the other hand, despite the excellent biodegradable behavior as being an integral constituent of the natural bone, the mechanical properties of ${\beta}$-tricalcium phosphate $(Ca_3(PO_4)_2;\;{\beta}-TCP)$ ceramics are not reliable enough for post operative load bearing application in human hard tissue defect site. One reasonable approach would be to mediate the features of the two by making a composite. In this study, ${\beta}$-TCP/Ti ceramic-metal composites were fabricated by spark plasma sintering in inert atmosphere to inhibit the formation of $TiO_2$. Composites of 30 vol%, 50 vol% and 70 vol% ${\beta}$-TCP with Ti were fabricated. Detailed microstructural and phase characteristics were investigated by FE-SEM, EDS and XRD. Material properties like relative density, hardness, compressive strength, elastic modulus etc. were characterized. Cell viability and biocompatibility were investigated using the MTT assay and by examining cell proliferation behavior.

• 보존과학연구
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• s.29
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• pp.149-162
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• 2008

Because stone cultural heritages in Korea are mostly situated outdoors without any notable protection, there are severe damages from physical, chemical and biological weathering. And this in turn causes deformation and structural damage. To counteract this problem and increase durability, various kinds of conservation materials are used in the conservation and restoration treatment. However, there are not many practical and technological experiments on this subject. Accordingly this research is for analysis of effect for treatment to make use a resin of the ethyl silicate for the granite in Mt. Nam of Gyeongju. It takes a long time to confirm the test result regarding durability and side effects of the conservatives after treatment. So we built up an artificial environment through freezing and melting test, and evaluated the conservation materials. As a result of this experiment, porosity and absorptivity was increased in accordance with processing of freezing and melting test. But other things such as elastic wave speed, elastic modulus, uniaxial compressive strength and tensile strength was decreased. It will make a plan to form a method of research systematically for mechanism and element of weathering and to elicit a correlation among experiment of artificial weathering and practical natural weathering from next research.

• Structural Engineering and Mechanics
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• v.21 no.5
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• pp.553-570
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• 2005

Dynamic and static analyses of existing structures are very important to obtain reliable information relating to actual structural properties. For this purpose a series of material test, dynamic test and static collapse test of the existing two brick chimneys, in Tokoname, are carried out. From the material tests, Young's modulus and compressive strength of the brick used for these chimneys are estimated to be 3200 MPa and 7.5 MPa, respectively. The results of static collapse test of the existing two brick chimneys are discussed in this paper and composed with the results from FEA (Finite Element analysis). From the results of dynamic tests, the fundamental frequencies of Howa and Iwata brick chimneys are estimated to be about 2.69 Hz and 2.93 Hz, respectively. Their natural modes are identified by ARMAV (Autoregressive Moving Average Vectors) model. On the basis of the static and dynamic experimental tests, a numerical model has been prepared. According to the European code (Eurocode n. 8: "Design of structures for earthquake resistance") non-linear static (Pushover) analysis of the two chimneys is carried out and they seem to be vulnerable to earthquakes with 0.25 to 0.35 g.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.145-148
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• 2006

Cold gas dynamic spray is a relatively new coating process by which coatings can be produced without significant heating during the process. Cold gas dynamic spray is conducted by powder sprayed by supersonic gas jet, and generally called the kinetic spray or cold-spray. Cold-spray was developed in Russia in the early 1980s to overcome the defect of thermal spray method. Its low process temperature can minimize thermal stress and also reduce the deformation of the substrate. Most researches on cold-spray have focused on micro scale coating, but our research team tried to apply this method to macro scale deposition. The macro scale deposition causes deformation of a thin substrate which is usually convex to the deposited side. In this research, the main cause of the deformation was investigated using 6061-T6 aluminum alloy and properties of deposited aluminum layer such as coefficient of thermal expansion, Elastic modulus, hardness, electric conductivity were measured. From the result of the analysis, it was concluded that compressive residual stress was the main reason of substrate deformation while CTE had little effect.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.975-978
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• 2008

To strengthen the technological competitiveness of the construction market in Korea, researches have been performed to replace the prescriptive design codes (PD) to the performance-based ones (PBD). As one of the basic requirements for PBDs, development of the optimized concrete material models for domestic applications have been tried by comparing and verifying the pre-existing models with the observations and quality evaluations of ready mixed concretes that are used in the domestic market. This paper shows the summary of the present state of the research progress in the areas of compressive strength and elastic modulus.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.23-27
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• 2015

Recently, the use of ion-exchange strengthened glass has increased sharply, as it is now used as the cover glass for smart phone devices. Therefore, many researchers are focusing on methods that can be used to strengthen ion-exchange glass. However, research on how the improved strength can be maintained under thermal environment of device manufacturing is still insufficient. We tested the degradation of the characteristics of ion-exchange soda-lime glass samples, including their surface compressive stress characteristics, the depth of the ion-exchange layer (DOL), flexural strength, hardness, and modulus of rupture (MOR) values. Degradation of the characteristics of the ion-exchange glass samples occurred when they were heat-treated at a temperature that exceeded $350^{\circ}C$.