• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.99-108
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• 2012

Ultra High Performance Concrete(UHPC) has compressive strength higher than 180 MPa. The use of steel fibers in the dense UHPC matrix increases tensile strength, ductility and bond strength between UHPC and rebars. However, to apply the advance material behavior of UHPC to the design of a structure, we need design formulas. The crack formula is one of them. This paper investigated experimentally the bond behavior of a rebar and K-UHPC, the UHPC developed by Korea Institute of Construction Technology, and, modified CEB-FIP crack formula based on the test. In addition, this paper tested the crack behavior of K-UHPC reinforced with rebars to verify the modified crack formula. The result showed that the modified formula is reasonable to predict the width of cracks in the reinforced K-UHPC structures.

• Geomechanics and Engineering
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• v.16 no.5
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• pp.495-501
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• 2018

Geogrid application that has proved to be an effective and economic method of reinforcing particles, is widely used in geotechnical engineering. The discrete element method (DEM) has been used to investigate the micro mechanics of the geogrid deformation and also the interlocking mechanism that cannot be easily studies in laboratory tests. Two types of realistically shaped geogrid models with square and triangle apertures were developed using parallel bonds in PFC3D. The calibration test simulations have demonstrated that the precisely shaped triangular geogrid model is also able to reproduce the deformation and strength characteristics of geogrids. Moreover, the square and triangular geogrid models were also used in DEM pull-out test simulations with idealized shape particle models for validation. The simulation results have been shown to provide good predictions of pullout force as a function of displacement especially for the initial 30 mm displacement. For the granular material of size 40 mm, both the experimental and DEM results demonstrate that the triangular geogrid of size 75 mm outperforms the square geogrid of size 65 mm. Besides, the simulations have given valuable insight into the interaction between particle and geogrid and also revealed similar deformation behavior of geogrids during pullout. Therefore, the DEM provides a tool which enable to model other possible prototype geogrid and investigate their performance before manufacture.

• Structural Engineering and Mechanics
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• v.81 no.2
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• pp.163-178
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• 2022

This paper aimed to study the local bond-slip behavior between ultra-high-performance concrete (UHPC) and a reinforcing bar after exposure to high temperatures. A series of pull-out tests were carried out on cubic specimens of size 150×150×150 mm with deformed steel bar embedded for a fixed length of three times the diameter of the tested deformed bar. The experimental results of the bond stress-slip relationship were compared with the Euro-International Concrete Committee (CEB-Comite Euro-International du Beton)-International Federation for Prestressing (FIP-Federation Internationale de la Precontrainte) Model Code and with prediction models found in the literature. In addition, based on the test results, an empirical model of the bond stress-slip relationship was proposed. The evaluation and comparison results showed that the modified CEB-FIP Model code 2010 proposed by Aslani and Samali for the local bond stress-slip relationship for UHPC after exposure to high temperatures was more conservative. In contrast, for both room temperature and after exposure to high temperatures, the modified CEB-FIP Model Code 2010 local bond stress-slip model for UHPC proposed in this study was able to predict the test results with reasonable accuracy.

• Journal of Welding and Joining
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• v.33 no.3
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• pp.25-31
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• 2015

Due to environmental regulations (RoHS, WEEE and ELV) of the European Union, electronics and automotive electronics have to eliminate toxic substance from electronic devices and system. Specifically, reliability issue of lead-free solder joint have an increasing demand for the car electronics caused by ELV banning. The authors prepared engine control unit and cabin electronics soldered with Sn-3.0Ag-0.5Cu (SAC305). To compare with the degradation characteristics of solder joint strength, thermal cycling test (TC), power-thermal cycling test (PTC) and series tests were conducted. Series tests were conducted for TC and PTC combined stress test using the same sample in sequence and continuously. TC test was performed at $-40{\sim}125^{\circ}C$ and soak time 10 min for 1000 cycles. PTC test was applied by pulse power and full function conditions during 100 cycles. Combined stress test was tested in accordance with automotive company standard. Solder joint degradation was observed by optical microscopy and environment scanning electron microscopy (ESEM). In addition, to compare with deterioration of bond strength of quad flat package (QFP) and chip components, we have measured lead pull and shear strength. Based on the series test results, consequently, we have validated of series test method for lifetime and reliability of Pb-free solder joint in automotive electronics.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.7
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• pp.743-748
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• 2011

The performance of HFO-1234yf as a substitute for R-134a was evaluated in a household freezer/refrigerator. A series of tests such as 'refrigerant charging test, pull-down test, cooling speed test, and energy consumption test were carried out under the AHAM (Association of Home Appliance Manufacturers) standard. The results of a drop-in test were compared with those of a test conducted using R-134a. A test under a severe ambient air condition ($43^{\circ}C$) was also conducted. The result shows that the refrigeration cycle performance of HFO-1234yf is as good as that of R-134a ; however, the diameter of capillary tube should be increased in order to improve its performance in the cooling speed test.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.9
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• pp.1858-1864
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• 2009

In this paper, we design a non-volatile memory IP, 1-kb one-time programmable (OTP) memory, used for power management ICs. Since a conventional OTP cell uses an isolated NMOS transistor as an antifuse, there is an advantage of it big cell size with the BCD process. We use, therefore, a PMOS transistor as an antifuse in lieu of the isolated NMOS transistor and minimize the cell size by optimizing the size of a OTP cell transistor. And we add an ESD protection circuit to the OTP core circuit to prevent an arbitrary cell from being programmed by a high voltage between the terminals of the PMOS antifuse when the ESD test is done. Furthermore, we propose a method of turning on a PMOS pull-up transistor of high impedance to eliminate a gate coupling noise in reading a non-programmed cell. The layout size of the designed 1-kb PMOS-type antifuse OTP IP with Dongbu's $0.18{\mu}m$ BCD is $129.93{\times}452.26{\mu}m^2$.

• Restorative Dentistry and Endodontics
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• v.39 no.2
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• pp.95-103
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• 2014

Objectives: This study evaluated the effect of three antioxidizing agents on pullout bond strengths of dentin treated with sodium hypochlorite. Materials and Methods: Root canals of 75 single-rooted human teeth were prepared. Fifteen teeth were irrigated with normal saline for a negative control group, and the remaining 60 teeth (groups 2 - 5) with 2.5% NaOCl. The teeth in group 2 served as a positive control. Prior to post cementation, the root canals in groups 3 - 5 were irrigated with three antioxidizing agents including 10% rosmarinic acid (RA, Baridge essence), 10% hesperidin (HPN, Sigma), and 10% sodium ascorbate hydrogel (SA, AppliChem). Seventy-five spreaders (#55, taper .02, Produits Dentaires S.A) were coated with silica and silanized with the Rocatec system and ceramic bond. All the prepared spreaders were cemented with a self-adhesive resin cement (Bifix SE, Voco Gmbh) in the prepared canals. After storage in distilled water (24 h/$37^{\circ}C$), the spreaders were pulled out in a universal testing machine at a crosshead speed of 1.0 mm/min. Pull-out strength values were analyzed by one-way ANOVA and Tukey's HSD test (${\alpha}$ = 0.05). Results: There were significant differences between study groups (p = 0.016). The highest pullout strength was related to the SA group. The lowest strength was obtained in the positive control group. Conclusions: Irrigation with NaOCl during canal preparation decreased bond strength of resin cement to root dentin. Amongst the antioxidants tested, SA had superior results in reversing the diminishing effect of NaOCl irrigation on the bond strength to root dentin.

• Tunnel and Underground Space
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• v.24 no.5
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• pp.395-403
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• 2014

In this study, a steel pipe type rockbolt manufactured from special material was developed which has high strength and lightweight characteristics. Achievement of grout filling between rockbolt and hole wall was investigated through grout injection tests. Yield force of the developed rockbolt was also examined through tensile tests, which was compared with that of the deformed bar type rockbolt. In addition, the strength and elongation properties of the developed rockbolt were investigated through pull-out tests at three domestic sites showing different RMR classes. It is finally supposed that the developed rockbolt can be suitable for the permanent tunnel support because it has high strength and high durability rather than deformed bar type rockbolt.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.2
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• pp.405-413
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• 2013

In this paper, a high-reliability differential paired 24-bit eFuse OTP memory with program-verify-read mode for PMICs is designed. In the proposed program-verify-read mode, the eFuse OTP memory can do a sensing margin test with a variable pull-up load in consideration of programmed eFuse resistance variation and can output a comparison result through a PFb (pass fail bar) pin by comparing a programmed datum with its read one. It is verified by simulation results that the sensing resistance is lower with $4k{\Omega}$ in case of the designed differential paired eFuse OTP memory than $50k{\Omega}$ in case of its dual-port eFuse OTP memory.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.320-329
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• 2005

The use of diverse methods for the retaining system has been continuously increased in order to maintain the stability during excavation. However, ground anchor system occasionally may have the restriction in urban excavation sites nearby the existing structures because of space limitation. In this case, soil nailing system with relatively short length of nails could be efficiently useful as an alternative method. The general soil nailing support system, however, may result in excessive deformations particularly in excavating the zone of weak soils or nearby the existing structures. Therefore, applying the pretension force to the soil nails then could play important roles to reduce deformations mainly in an upper part of the nailed-soil excavation system as well as to improve the local slope stability. In this study, a newly modified soil nailing technology named as the PSN(Pretention Soil Nailing) is developed to reduce both facing displacements and ground surface settlements during top-down excavation process as well as to increase the global slope stability. Up to now, the PSN system has been investigated mainly focusing on an establishment of the design procedure. In the present study, the field tests including pull-out tests were fulfilled to investigate the behavior of characteristics for PSN system. All results of tests were also analyzed to provide a fundamental and efficient design.