• Polymer(Korea)
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• v.28 no.4
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• pp.285-290
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• 2004

Nondestructive damage sensitivity of carbon nanotube(CNT) and nanofiber (CNF)/epoxy composites with their adding contents was investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison with CNT and CNF. The fracture of carbon fiber was detected by acoustic emission (AE), which was correlated to the change in electrical resistance, ΔR under double-matrix composites (DMC) test. Stress sensing on carbon nanocomposites was performed by electro-pullout test under uniform cyclic loading. At the same volume fraction, the damage sensitivity for fiber fracture, matrix deformation and stress sensing were highest for CNT/epoxy composite, whereas for CB/epoxy composite they were the lowest among three carbon nanomaterials (CNMs). Damage sensitivity was correlated with morphological observation of carbon nanocomposites. Homogeneous dispersion among CNMs could be keying parameters for better damage monitoring. In this study, damage sensing of carbon nanocomposites could be evaluated well nondestructively by the electrical resistance measurement with AE.

• Journal of the Korean Geotechnical Society
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• v.25 no.7
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• pp.5-10
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• 2009

The ground anchor is not usually used in soft clay and loose sand, because the pullout resistance of anchors can not be guaranteed. However, there is a method to increase the capacity of anchors using electric discharge geotechnical technologies, which are also known as pulse discharge and electric-spark technologies. The pulse-discharge anchor has a bulbed (or underreamed) bond length that is expanded by high voltage electrokinetic pulse energy. 24 anchors were installed in the weathered soil and sandy clay at the Geotechnical Experimentation Site at Sungkyunkwan University in Suwon, Korea. In this study, in order to define a relation between expansion rate of the anchor diameter and ultimate load, anchor load tests were carried out in accordance with testing procedures by AASHTO (AASHTO 1990) and FHWA (Weatheb 1998). And then several anchors were exhumed to measure the diameter of the pulse discharge anchors.

• Proceedings of the KOSOMBE Conference
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• v.1995 no.05
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• pp.19-22
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• 1995

A biomechanical study was made to demonstrate the superior mechanical performance of the newly designed Miniplate staple to the conventional Coventry staple in high tibial osteotomy(HTO). Using twenty fresh porcine tibiae, the fixational strengh of the two different types of staple in HTO was compared. To minimize the error due to the specimen-to-specimen individuality, the bone mineral density of the tibiae was measured with a bone densitometry (Dual photon absorptionometer, Luner, USA) and those with $0.8\;{\sim}\;1.2\;gm/cm^2$ at the proximal tibia was used in the biomechanical test. Testing was performed on a material testing system (Autogram ET-5, Shimatzu, Japan) with aid of a commercial data processor (IBM 80386/ ASYST). Using two differant loading modes, 'pull-out' and 'push-out', the maximum resistant force required to release the staple from the substrate bone was recorded. In the pull-out test, ten non-osteotomized specimens were used and the staple was pullout by subjecting an axial tension on the head of the staple inserted. While in the pull-out test where ten tibiae osteotomized in the usual way of HTO were used, the staple was not directly loaded. In this testing, as a mimic condition of the natural knee, the distal part of the specimen tibia was pushed horizontally in order for the staple to be pulled out while the proximal tibia was fixed. The pull-out strength of Coventry staple and miniplate staple were found to be $27.88\;{\pm}\;5.12\;kgf$ and $182.47\;{\pm}\;32.75\;kgf$, respectively. The push-out strength of Coventry staple and miniplate staple were $18.40\;{\pm}\;4.47\;kgf$ and $119.95\;{\pm}\;19.06\;kgf$, respectively. The result revealed that miniplate staple had the pull-out/ push-out strength at least fivetimes higher than Coventry staple. Based on the measured data, it was believed that the newly designed miniplate staple could provide much better postoperative fixation in HTO. The postoerative application of long leg casting may not be needed after HTO surgery.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.251-260
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• 2001

Damage Profess of CFRP laminates under monotonic tensile test was characterized by the correlation between Acoustic Emission(AE) and Ultrasonic Test(UT). The amplitude distribution of AE signal from a specimens is an aid to the determination of the extent of the different fracture mechanism such as matrix crack, debonding, fiber pullout and fiber fracture as load is increased. In addtion, the characteristics of ultrasonic amplitude attenuation are useful lot analysis of the different type of fracture mechanism. Different orientation of carbon fiber reinforced plastic specimens were used to investigate the AE amplitude range and ultrasonic amplitude attenuation. Finally, loading-unloading tests were carried out to check Felicity effect. During the tests, ultrasonic amplitude attenuation was investigated at the same time and compared with AE parameters. The result showed that two parameters of both AE and UT could be effectively used for analysis of fracture mechanism in CFRP laminates.

• Steel and Composite Structures
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• v.1 no.3
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• pp.329-340
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• 2001

Cyclic response of "shear" connections between steel outrigger beams and reinforced concrete core walls is presented in this paper. The connections investigated in this paper consisted of a shear tab welded onto a plate that was connected to the core walls through multiple headed studs. The experimental data from six specimens point to a capacity larger than the design value. However, the mode of failure was through pullout of the embedded plate, or fracture of the weld between the studs and plate. Such brittle modes of failure need to be avoided through proper design. A capacity design method based on dissipating the input energy through yielding and fracture of the shear tab was developed. This approach requires a good understanding of the expected capacity of headed studs under combined gravity shear and cyclic axial load (tension and compression). A model was developed and verified against test results from six specimens. A specimen designed based on the proposed design methodology performed very well, and the connection did not fail until shear tab fractured after extensive yielding. The proposed design method is recommended for design of outrigger beam-wall connections.

• Journal of The Korean Digital Architecture Interior Association
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• v.12 no.3
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• pp.59-66
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• 2012

Autoclaved Lightweight Concrete(ALC) features such as a high performance insulation, the fire resistance, the advantage of easy handing construction, and lightweight panels applied the curtain wall system. ALC materials are certified as non-toxic environmental and eco-friendly productions. But ALC external panels mixed with blast furnace slag pounder and silica fume have to be coated with a stucco compound or plaster because of resisting the ambient environment. This study is that mixing tests to evaluate a performance analysis of exterior paints to be make-up pigments(organic or inorganic) coated with panel surface. Testing compared by KS F 2476; flow test, KS F 2426; compression strength test, KS F 2762; bond strength test. In results, the case of the inorganic binder, ratio of alumina cement : anhydrite is 90:10 to 80:20 at the highest level of intensity. In the case of the organic binder, adhesive strength rating at surface of ALC, the pullout strength is below 0.5 $N/mm^2$ but the normal concrete is over 2.0$N/mm^2$. A contents ratio of EVA resin is more than 3% and then bond strength is effectively.

• Computers and Concrete
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• v.24 no.5
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• pp.413-422
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• 2019

In this study, 3D Meso-scale finite-element model is presented to study the mechanical behavior of steel microfiber-reinforced polymer concrete considering the random distribution of fibers in the matrix. The composite comprises two separate parts which are the polymer composite and steel microfibers. The polymer composite is assumed to be homogeneous, which its mechanical properties are measured by performing experimental tests. The steel microfiber-polymer bonding is simulated with the Cohesive Zone Model (CZM) to offer more-realistic assumptions. The CZM parameters are obtained by calibrating the numerical model using the results of the experimental pullout tests on an individual microfiber. The accuracy of the results is validated by comparing the obtained results with the corresponding values attained from testing the steel microfiber-reinforced polymer concrete incorporating 0, 1 and 2% by volume of microfibers, which indicates the excellent accuracy of the current proposed model. The results show that the microfiber aspect ratio has a considerable effect on the mechanical properties of the reinforced polymer concrete. Applying microfibers with a higher aspect ratio improves the mechanical properties of the composite considerably especially when the first crack appears in the polymer concrete specimens.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.259-271
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• 2006

This paper aims to predict the corrosion of a fully cement-grouted rockbolt induced by chloride diffusion in a cement mortar grout. From the viewpoint of the long-term durability, a rockbolt may be deteriorated by chemical components, such as sulphate and chloride, in groundwater. Especially, the steel rod of a rockbolt is corroded mainly by chloride. The rockbolt corrosion results in the volume expansion of a rod and then the cracking of a cement grout. In this study, the chloride diffusion coefficient of a cement mortar grout was used to evaluate the possibility of rockbolt corrosion by chloride, and to predict the long-term durability of a rockbolt. The electric acceleration test method was adopted to measure the chloride diffusion coefficient. In addition, a simple pullout testing system was newly proposed to measure the pullout capacity of a rockbolt more easily in a laboratory condition. From the experiments, it was showed that the chloride could diffuse in the cement grout more easily than in ordinary concrete materials. As a result, it was considered that a rockbolt might be easily corroded in a short term by the diffusion of chemical components with high concentration, although it was fully grouted.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.69-75
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• 2014

Rock fall protection system installed against rock slope is one of the most conventional way to protect nearby infra structures. Despite of wide application of typical rectangular nets, virtually installed to protect rock slope face, several problems have also been pointed out up to date. Rectangular draped nets are vulnerable to a sudden external shock such as rock fall, because it doesn't have any systematical buffers or shock absorbers. Furthermore, it has been widely recognized from the some cases of rock fall accident in Korea that rock fall protection nets cause wide range of failure in the rock slope faces due to insufficient pullout bearing capacity of fixing parts. Therefore, in this study, we tried to make a consideration about the problems of existing standard rock fall protection nets in Korea, and develop a new type of hexagonal net with a shock absorber based on design rock fall energy. In this paper, laboratory and full scale test procedure is described to analysis the performance of newly developed hexagonal rock fall net, and the key results are presented and discussed.

• Journal of Korean Society of Steel Construction
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• v.10 no.4 s.37
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• pp.629-639
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• 1998

This paper summarizes the results of full-scale cyclic seismic performance tests on three column-tree type steel moment connections. Each test specimen consisted of a $H-600{\times}200$ beam and a $H-400{\times}400$ column of SS41 (SS400). Key parameter included was column PZ (panel zone) strength relative to beam strength. The seismic performance of specimen with stronger PZ tended to be inferior. Total plastic rotations available in the specimens ranged from 1.8 to 3.0 (% rad). The limited test results in this study seem to support the speculation that permitting PZ yielding shall be more beneficial to enhancing total plastic rotation capacity of the moment connection. Beam flange fracture across the heat affected zone and divot-type pullout of the column flange were observed in the tests. A conceptual mechanical model consistent with observed test results was also sought.