• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.55-62
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• 2000

A surface acoustic wave method for the evaluation of small fatigue crack initiated from a pit-type surface flaw is presented. In-situ ultrasonic experiments are performed for aluminum 2024-T3 alloy samples under the fatigue test. During the fatigue test, the surface acoustic wave reflection signal from the pit and crack is measured under different hold-stress levels. From the measured and predicted surface wave reflections the depths of fully and partially open cracks are determined and results are verified by comparing with SEM fractography The crack opening behavior of the fatigue crack is evaluated from the predicted effective crack depths. The method developed in this study can be applied to monitor and characterize crack initiation and propagation from pit-type surface flaws in the early stage of fatigue life.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.5
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• pp.672-686
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• 1999

The purpose of this study was to compare the casting problem and corrosion behavior in two types of HL Hexed abutments of the Steri-Oss system ; gold/plastic coping and gold coping. The anodic Polarization behavior, the galvanic corrosion between abutments and Type III gold alloys, before and after casting were analyzed, and the crevice corrosion of casting samples was analyzed with the CPPT test and the SEM. The results are as follows : 1. Anodic polarization behavior of samples ; Before casting, gold/plastic coping and gold coping was shown to have a similar corrosion pat-terns. Type III casting gold alloy was shown to have a lower corrosion potential and passivation film. Corrosion potential of the case of gold/plastic coping after casting was higher than that of gold coping, but the region of passivation film for gold/plastic coping was smaller than that of gold coping. 2. Galvanic corrosion behavior of samples ; Contact current density between casting gold alloys and gold/plastic before casting was higher than that between gold coping and casting gold alloy Galvanic corrosion of samples after casting was shown to have similar contact current density 3. Crevice corrosion behavior of samples ; Crevice corrosion resistance of casting sample using gold coping was lower than that of cast-ing sample using gold/plastic coping, and a severe corrosion pattern was observed at the abutment-casting gold alloy interface by the SEM.

• Geomechanics and Engineering
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• v.29 no.3
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• pp.311-320
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• 2022

TBM concrete segment requires a higher level of material properties compared to general concrete structures due to difficulties in maintenance and uncertainty in ground conditions. In this regard, recently, as one of the methods to achieve enhancement effect on concrete strength, many researchers have been focusing on adding CNTs to concrete mixture. However, even CNTs do not compensate the weakness that concrete exhibits brittle behavior after cracking. Separately, over the past few decades, a number of studies have been conducted on fiber reinforced concrete which exhibits ductile behavior due to fibers bridging cracks. However, only limited studies have been conducted to employ the advantages of the both materials together. In this study, an experimental program has been conducted to investigate the effect of CNTs on the workability and the compressive behavior of PVA-ECC which exhibits ductile tensile behavior with well-distributed cracks even without a conventional rebar. In addition to the compression test, SEM analysis has been also conducted for detailed investigation in the microstructure. The variable was the CNTs mix ratio, which were set to 0.00, 0.25, and 0.50 wt.% to the binding materials. It was observed though the test results that as the CNTs mix ratio increased, the workability considerably decreased with the reduced slump and slump flow. From the compression test results, it was also investigated that the compressive behavior was improved since the compressive strength, the strain corresponding to the compressive strength, and the modulus of elasticity increased with an increase of CNTs mix ratio. The contents of this paper will be useful for relevant research areas such as fiber reinforced concrete with CNTs which might be applied for high performance TMB concrete segments.

• Journal of the Korean Applied Science and Technology
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• v.39 no.2
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• pp.220-232
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• 2022

In this study, 223 people were sampled from February 1 to March 11, 2022, and causal relationship analysis (SEM) was performed. First, a causal relationship was established between coaching behavior and leader trust, and second, a causal relationship was established between leader trust and re-enrollment. Finally, although it was partially adopted between coaching behavior and re-registration, an indirect effect was also derived that the effectiveness of behavior existed as an indirect effect of trust in the leader in the relationship between autonomous behavior and re-registration. Therefore, coaching behavior perceived by customers is influenced by various variables, and trust in leaders appears to exert a huge influence on golf course management performance, emphasizing that human service is a part that needs attention in the changing golf market. It is thought that a management strategy based on the results and this study is necessary.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.529-541
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• 2016

Under the interaction between dam body, dam foundation and external environment, the dam structural behavior presents the time-varying nonlinear characteristics. According to the prototypical observations, the correct identification on above nonlinear characteristics is very important for dam safety control. It is difficult to implement the description, analysis and diagnosis for dam structural behavior by use of any linear method. Based on the rescaled range analysis approach, the algorithm is proposed to identify and extract the fractal feature on observed dam structural behavior. The displacement behavior of one actual dam is taken as an example. The fractal long-range correlation for observed displacement behavior is analyzed and revealed. The feasibility and validity of the proposed method is verified. It is indicated that the mechanism evidence can be provided for the prediction and diagnosis of dam structural behavior by using the fractal identification method. The proposed approach has a high potential for other similar applications.

• Structural Engineering and Mechanics
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• v.59 no.1
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• pp.15-36
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• 2016

The components of the seismic behavior factor of RC frames are expected to change as structural redundancy increases. Most researches indicate that increasing redundancy is desirable in response to stochastic events such as earthquake loading. The present paper investigated the effect of redundancy on a fixed plan for seismic behavior factor components and the nonlinear behavior of RC frames. The 3D RC moment resistant frames with equal lateral resistance were designed to examine the role of redundancy in earthquake-resistant design and to distinguish it from total overstrength capacity. The seismic behavior factor and dynamic behavior of structures under natural strong ground motions were numerically evaluated as the judging criteria for structural seismic behavior. The results indicate that increasing redundancy alone in a fixed plan cannot be defined as a criterion for improving the structural seismic behavior.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.781-791
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• 2023

Lateral pressure plays a significant role in the stress-strain relationship of compressed concrete. Concrete's internal cracking resistance, ultimate strain, and axial strength are improved by confinement. This phenomenon influences the nonlinear behavior of reinforced concrete columns. Utilizing behavior factors to predict the nonlinear seismic responses of structures is prevalent in seismic codes, and this factor plays a vital role in the seismic responses of structures. This study aims to evaluate the confining action on the behavior factor of reinforced concrete moment resisting frames (RCMRFs) with shear walls (SWRCMRFs). To this end, a diverse range of mid-rise SW-RCMRFs was initially designed based on the Iranian national building code criteria. Second, the stress-strain curve of each element was modeled twice, both with and without the confinement phenomenon. Each frame was then subjected to pushover analysis. Finally, the analytical behavior factors of these frames were computed and compared to the Iranian seismic code behavior factor. The results demonstrate that confining action increased the behavior factors of SW-RCMRFs by 7-12%.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.307-310
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• 2009

Nowadays, the usage of high strength steel has been growing in automobile industry mainly as structural parts since for its lightweight and high strength properties the oil crisis happened. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot press forming. The high-strength steel sheets are in so me instances used with an Al-Si-coating with a view to prevent scaling of components during hot press forming. How ever, friction and fracture characteristics of Al-Si-coated high-strength steel during hot press forming process have not yet been investigated. In this paper, the formed parts which were formed in hot bending process were investigated by using EDS. SEM and nano indenter in order to analysis the coating layer behavior.

• Structural Engineering and Mechanics
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• v.67 no.5
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• pp.545-553
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• 2018

Mode II delamination propagation is an important damage mode in laminated composites and this paper aims to investigate the behavior of this damage in laminated composite materials using acoustic emission (AE) technique. Three different lay-ups of glass/epoxy composites were subjected to mode II delamination propagation and generated AE signals were recorded. In order to investigate the propagation of delamination behavior of these specimens, AE signals were analyzed using Wavelet Packet Transforms (WPT) and Fast Fourier Transform (FFT). In addition, conventional AE analyses were used to enhance understanding of the propagation of delamination damage. The results indicate that different fracture mechanisms were the main cause of the AE signals. The dominant mechanisms in all the specimens were matrix cracking, fiber/matrix debonding and fiber breakage, with varying percentage of the damage mechanisms for each lay-up. Scanning Electron Microscopy (SEM) observations were in accordance to the AE results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.445-445
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• 2008

The behavior of ion trapping and migration in the yittria-stabilized zirconia pellets following high dose ion beam irradiation have been studied using SEM, EDX, and TGA. The ion beam was irradiated at room and higher temperatures and the differences in their results were interpreted in terms of dynamic annealing effects. The SRIM calculation was also performed to explain the cross sectional SEM image of the electrolytes.