• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1741-1751
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• 2013

The main purpose of this study is to investigate the static behavior of a prestressed concrete (PSC) girder using pre-tension method. A 30m long full-scale pretension PSC girder is fabricated by the portable fabrication system and tested. All results have been compared to those obtained from F.E.A results. Deflections at the middle of girders have been measured for evaluation. Also, strains of concrete at the middle of span have been measured. From the results of experimental, the load when initial crack was developed was obtained to be 1.75 time the unfactered design load in the full-scale girder specimen. Also, the data of specimen are satisfied the desgin requirements of ductility on the Korea Bridge Design Specification(2010). In service state, the vertical deflection at center of test specimen when a initial crack was developed is satisfied the vertical deflection requirement under live load of the Korea Bridge Design Specification(2010). To verify the experimental results, we numerical analyze the test and confirmed that the data were similar with results from the test above. The pretension girder fabricated in site were found to have enough strength for safety under and after construction.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.155-160
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• 2008

Using a three-dimensional (3-D) FE analyses, this paper provides the shape optimization of the standard test specimen for the torsion test, as well as a method for analyzing effects of misalignment under the angular and concentric misalignment. For verification, FE analysis is performed, which is designed for the perfectly full-model. To optimize the design shape of the torsion-controlled fatigue test specimen, we performed sensitivity analysis using shape parameters. Additionally, two kinds of misalignment (angular misalignment and concentric misalignment) are applied to the circular and tubular specimens to show effects of misalignments in the FE analysis. The present results will provide valuable information for designing shafts for every kind of mechanical system under torsional force.

• Applied Microscopy
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• v.44 no.4
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• pp.133-137
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• 2014

We suggest a facile transmission electron microscopy (TEM) specimen preparation method for the direct (polymer-free) transfer of layer-area graphene from Cu substrates to a TEM grid. The standard (polymer-based) method and direct transfer method were by TEM, high-resolution TEM, and energy dispersive X-ray spectroscopy (EDS). The folds and crystalline particles were formed in a graphene specimen by the standard method, while the graphene specimen by the direct method with a new etchant solution exhibited clean and full coverage of the graphene surface, which reduced several wet chemical steps and accompanying mechanical stresses and avoided formation of the oxide metal.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.13-18
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• 2004

The objective of this study is to investigate fracture toughness and fatigue crack propagation behavior in the Reduced Activation Ferritic Steel (RAFs) JLF-I. The fracture toughness tests were performed with various size(plane size and thickness) and various side groove of specimens. The fatigue crack propagation behavior of the JLF-I steel was investigated by the constant-amplitude loading test for the stress ratios R=O.I, 0.3 and 0.5 respectively. The effects of stress ratios and specimen size on the fatigue crack growth behaviors for JLF-I steel were discussed within the Paris law. The test results showed the standard CT specimen with the side groove of 40 % represented a valid fracture toughness. The fracture resistance curve increased with increasing plane size and decreased with increasing thickness. However, the fracture resistance curve of half size specimen was similar to that of the standard specimen. The fatigue crack propagation rate of a half size specimen was similar to that of a full size specimen at the stress ratios of 0.1, 0.3 and 0.5 respectively. The fatigue crack propagation behavior of this material were evaluated by using a half size specimen.

• Journal of the Korean Institute of Gas
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• v.2 no.4
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• pp.42-46
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• 1998

Miniaturized specimen technology Permits mechanical behavior to be determined using a minimum volume of material. The technology is useful in case of not collecting a large amount of materials from industrial equipments. Five kinds of accelerated degradation materials were prepared by isothermal aging heat treatment at $630^{\circ}C$. Three kinds of specimens were prepared for impact testing. In order to increase plastic constraint of subsize specimen, side-groove was introduced. Results between subsize and full size impact testing were compared. Size effects correlations were developed for the impact properties of turbine rotor material. These correlations successfully predict the ductile brittle transition temperature (DBTT) of full size Charpy impact specimens based on subsize specimen data.

• Journal of the Korean Society of Safety
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• v.28 no.4
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• pp.26-32
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• 2013

A digital image correlation(DIC) method is a whole-field measurement technique that acquires surface displacements and strains from images information which characterized a random speckle as intensity grey levels. Recently years, this DIC method is being developed and used increasingly in various research. In this study, we tried to apply to aluminum alloy(Al 6061-T6) using DIC method and strain gauge. DIC results demonstrated the usefulness and ability to determine a strain. The test specimen used in this study was an aluminum alloy(Al 6061-T6, thickness 1 mm). For a strain measurement, a strain gauge was attached at the center of a specimen. A specimen was lightly sprayed with a white paint and a black dot pattern was sprayed on its fully dried white surface to obtain a random speckle. The experimental apparatus used to perform the tensile test consisted of universal dynamic tester(5 kN; T.O. Co.) under displacement speed of 0.5, 1.0 and 3.0 mm/min. A Model 5100 B Scanner(V. Co.) used to obtain a strain. A CCD camera connected to a PC uses to record the images of the specimen surface. After acquisition, the images were transferred to PC where the DIC software was implemented. An acquired image was evaluated by the DIC program. DIC method for displacement and strain was suggests and it results show a good consistent remarkably. DIC results demonstrated the usefulness and ability to determine surface strain was better than by using classical measurements. The strain field measurement using a DIC is so useful that it can be applied to map strain distributions at a full area. DIC method can evaluate a strain change so it can predict a location of fracture. The findings of the investigation suggest that the DIC method is an efficient and reliable tool for full-field monitoring and detailed damage characterization of materials.

• Earthquakes and Structures
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• v.25 no.2
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• pp.113-123
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• 2023

A novel type of buckling restrained brace with built-up angle steel was developed. The core segment was formed by welding angle steel, and the middle section was reduced by cutting technology to solve the problem that the end of BRB was easy to buckle. The experimental program has been undertaken to study the performance of BRBs with different unbonded materials (silica gel, kraft paper) and different filler materials (ordinary concrete, full light-weight concrete). Four specimens were designed and fabricated for low cycle reciprocating load tests to simulate horizontal seismic action. The failure mode, hysteretic curves, tension-compression unbalance coefficient and other mechanical parameters were compared and analyzed. The finite element software ABAQUS was used to conduct numerical simulation, and the simulation results were compared with the experimental phenomena. The test results indicated that the hysteretic curve of each specimen was plump. Sustaining cumulative strains of each specimen was greater than the minimum value of 200 required by the code, which indicated the ductility of BRB was relatively good. The energy dissipation coefficient of the specimen with silica gel as unbonded material was about 13% higher than that with kraft paper. The experimental results were in good agreement with the simulation results.

• Journal of the Korean Society of Safety
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• v.25 no.2
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• pp.7-11
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• 2010

Difficulties associated with full-scale pipe tests are rather obvious. That is, it is not only difficult to perform them but also very expensive and it requires lots of experience. And the process of the fracture test for the pipe specimen is very difficult and complicated. Because the pipe specimen, the test jig and the test equipment are very large and heavy, it requires lots of costs and times. In this study, to easily perform the fracture toughness test for a pipe specimen, load line displacement data was obtained using the image processing method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.7
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• pp.1159-1169
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• 2003

This paper investigates the effects of T-stress and plastic hardening mismatch on the interfacial crack-tip stress field via finite element analyses. Plane strain elastic-plastic crack-tip fields are modeled with both MBL formulation and a full SEC specimen under pure bending. Modified Prandtl slip line fields illustrate the effects of T-stress on crack-tip constraint in homogeneous material. Compressive T-stress substantially reduces the interfacial crack-tip constraint, but increases the J-contribution by lower hardening material, J$\_$L/. For bimaterials with two elastic-plastic materials, increasing plastic hardening mismatch increases both crack-tip stress constraint in the lower hardening material and J$\_$L/. The fracture toughness for bimaterial joints would consequently be much lower than that of lower hardening homogeneous material. The implication of unbalanced J-integral in bimaterials is also discussed.

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1261-1265
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• 1999

Effect of SiC particle size of the densification of Al2O3-SiC composite during pressureless sintering was investigated. Two types of SiC powders having average particle size of 0.15${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$ were used. Densification rate of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was slower than that of the specimen containg 3${\mu}{\textrm}{m}$ SiC particles. Although the relative density of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was below 90% of theoretical density after sintering at 155$0^{\circ}C$ the complete closure of open pores occurred. Therefore full densification could be obtained by subsequent HIP. On the other hand in the specimen containing 3${\mu}{\textrm}{m}$ SiC particles the complete closed pore was observed at 95% of theoretical density. Such a fast pore closure in the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles is likely to occur as a result of dense reaction layer formation on the specimen surface which is attributed to the high reactivity of small size particles with sintering atmosphere.