Kwang Hwan Oh

Jangsung (South Korea)

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Kyung Seop Han

Pohang University of Science and Technology

Sungho Jeong

Gwangju Institute of Science and Technology

Jun Ho Jang

Samsung Medical Center

Hyundeok Im

Samsung (South Korea)

C.K. Jung

Pohang Iron and Steel (South Korea)

Kyung Seok Oh

Pohang Iron and Steel (South Korea)

Nam Hwang

Korea Photonics Technology Institute

Jason S. Koh

Korea Institute of Nuclear Safety

Dug Young Kim

Yonsei University

M K Lee

Gwangju Institute of Science and Technology

Cooperative Institutions

Gwangju Institute of Science and Technology

Ministry of Health and Welfare

Chonnam National University Hospital

Chonnam National University

Sungkyunkwan University

Jangsung (South Korea)

Yonsei University

Pohang University of Science and Technology

Korea Institute of Industrial Technology

Cardiovascular Institute of the South

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Detection and Evaluation of Localized Damage under Creep-Fatigue Loading at 1000°F Using Acoustic Emission Technique

Diffusion and defect data, solid state data. Part B, Solid state phenomena/Solid state phenomena (2006)

Kwang Hwan Oh Jun Ho Jang C.K. Jung Kyung Seop Han

Acoustic emission (AE) technique was applied as a non-destructive test method to detect and evaluate the localized damage at high temperature environment. The creep-fatigue crack growth tests were carried out with the acquisition of AE signal at 1000°F. Under trapezoidal waveform loadings, AE results showed different features according to each damage mode. During the creep period, low and steady emissions were shown, while emissions were burst and high counts rate was recorded during the fatigue loading. Based on these characteristics, damage contribution was expressed in terms of acoustic emission parameter as a part-time monitoring method. Comparisons of damage contribution with respect to lifetime showed the transient behavior from cycle-dependent to time-dependent process. In case of full-time monitoring, bilinear behavior between AE counts and life was represented. From both monitoring results, it was confirmed that creep and fatigue damage can be characterized by means of emission features and AE is possible way to evaluate the localized damage at elevated temperature.

Acoustic Emission

SIGNAL (programming language)

Transient (computer programming)

10.4028/www.scientific.net/ssp.110.45

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Interrelationship between Stress Intensity Factor and Acoustic Emission Parameter in the Opening Mode Fatigue Crack Propagation

Diffusion and defect data, solid state data. Part B, Solid state phenomena/Solid state phenomena (2006)

Kwang Hwan Oh Kyung Seop Han

Interrelationship between stress intensity factor and acoustic emission parameter in the opening mode fatigue crack propagation was investigated. Under various conditions with different cyclic amplitudes and crack lengths, counts rate behavior was examined. Experimental results indicated that stress intensity factor range ( K) could be divided into two parts according to its relationship with counts rate. This interrelationship was keeping the same trend regardless of load range or crack length for all tested materials. However, more distinct interrelationship was shown as the material has lower yield strength and higher ductility. Overall experimental data were somewhat scattered since sensitive characteristics of acoustic emission method. However, these empirical relations indicated that AE counts rate was uniquely correlates with single parameter, K.

Acoustic Emission

Mode (computer interface)

Intensity

10.4028/www.scientific.net/ssp.110.71

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Addendum to: Picosecond pulse generation for visible semiconductor laser operating at 650‐NM wavelength with the use of the gain‐switching technique

Microwave and Optical Technology Letters (2002)

Kwang Hwan Oh Nam Hwang Jason S. Koh Dug Young Kim

Abstract Originally published Microwave Opt Technol Lett 35: 65–67, 2002. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 342–342, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10584

Addendum

Picosecond

10.1002/mop.10584

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Processing and Characterization of Graphite Nanofibers Reinforced Aluminum Matrix Composites

Key engineering materials (2006)

Jun Ho Jang Kwang Hwan Oh Seongkwang Heo Kyung Seop Han

Graphite nanofibers (GNFs) reinforced aluminum matrix composites have been fabricated successfully by powder metallurgy methods. The GNF-Al mixtures were prepared through ultrasonication and ball milling. The GNF-Al composites were consolidated by hot isostatic pressing (HIP) and then a high density of compacts could be obtained. The microstructure and the distribution of nanofibers in matrix material were investigated by microscopy observations. A uniform distribution of nanofibers in aluminum matrix was obtained. The mechanical properties were measured by microhardness and compression tests. The optimal contents of nanofibers were determined in view of the mechanical properties. The results of thermal tests indicate that the addition of nanofibers were enhanced the thermal conductivity but, the dimensional stability such as thermal expansion was not improved significantly.

Powder Metallurgy

Hot pressing

Hot isostatic pressing

Thermal Stability

10.4028/www.scientific.net/kem.306-308.1067

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Development of Universal Test Method to Evaluate the Plastic Deformation of Sheet Metal

Key engineering materials (2011)

Kyung Seok Oh Kwang Hwan Oh Jun Ho Jang Kyung Seop Han

Universal test method to evaluate sheet metal formability was developed using finite element method based on axiomatic design. The newly developed formability test intended to generate the various modes of deformation and to control the onset of failure independently under each mode of deformation. The functional requirements (FRs) and the design parameters (DPs) of the test system were defined on axiomatic design approach and decomposed until the design reaches final stage. The independence axiom was applied throughout the design process to maintain the hierarchical independence of the formability test system. The flow diagram representing the system architecture was introduced after decomposition to give a help to establish the systematic design procedures and to determine the design parameters. Numerical simulation was carried out to determine the specific value of DPs which satisfies the FRs. Numerical results showed that modes of deformation varies accompanying various strain paths and good controllability of sheet forming is obtained for different kinds of materials. Experimental work was finally conducted to validate the proposed design. Stamping results represented that the outcome of the deformed geometry and strains are in good agreement with the numerical results.

Axiomatic design

Stamping

Independence

10.4028/www.scientific.net/kem.462-463.961

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Acoustic Emission as a Tool of Fatigue Assessment

Key engineering materials (2006)

Kyung Seop Han Kwang Hwan Oh

A series of laboratory investigations concerned about fatigue assessment with acoustic emission method was presented. Fatigue aspects including cumulative fatigue damage, fatigue crack growth and creep-fatigue interaction were considered. As a basic approach, residual strength and acoustic emission characteristics of fatigue damaged materials were considered from the nominal stress-life (S-N) viewpoint. Acquired signal indicated that counts emission quantity can be a good measure of cumulated fatigue damage. In the fatigue crack growth approach, interrelationship between acoustic emission parameter and stress intensity factor was examined with different stress level and crack length. Experimental results were somewhat scattered since sensitive characteristics of acoustic emission method. However, their empirical relation indicated that counts rate correlated with fracture mechanics parameter. Finally, acoustic emission application was extended to the creep-fatigue interaction at elevated temperature. Emission response under each damage mode was compared and characterized. Based on these characteristics, creep-fatigue interaction was evaluated by use of acoustic emission parameter. Overall investigations concluded acoustic emission is very effective tool of fatigue assessment.

Acoustic Emission

Fatigue limit

Residual strength

Paris' law

10.4028/www.scientific.net/kem.306-308.271

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Citations (6)

Consideration of a Local Aluminum-Induced Crystallization Process Guided along the µ-Holes Fabricated with fs Laser Pulses

Journal of Laser Micro/Nanoengineering (2014)

Kwang Hwan Oh

A polycrystalline silicon (poly-Si) film is produced by the aluminum-induced crystallization (AIC) process guided along the µm-sized laser hole and characterized for application to a seeding layer of poly-Si solar cells.We investigated the crystallization of amorphous silicon (a-Si) films using the AIC process with a structure of glass/Al/SiO 2 /a-Si in which the silicon oxide (SiO 2 ) layer has holes with 1 ~ 2 µm in diameter so that the AIC process occurred only through the hole.The purpose of our experiment is to see the poly-Si grain growth, if possible, from a single poly-Si seed in the AIC process.For the experiment, the microhole array of about 1 ~ 2 µm in diameter is prepared in the SiO 2 layer of the structure using femtosecond laser pulses and the AIC process is carried out with the conventional heat treatment procedure.As results, it is observed that the crystallization of a-Si occurred only in the area under the microhole and the grain of poly-Si grew to the size of over 3 µm.Furthermore, it was shown that the grain grew with one dominant crystal orientation.

10.2961/jlmn.2014.03.0016

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Investigation of Thermochemical Reaction of Metallic Grooves Manufactured with Laser Micromachining in Liquid

Journal of Laser Micro/Nanoengineering (2016)

Kwang Hwan Oh

Chemical reaction governing the overall etching process is the most significant factor in the determination of etching characteristics in laser-induced etching. A method of the sample preparation for measuring chemistry of the etchant and etched metallic groove is demonstrated. Also, chemical analyses of the used etchant and etched groove and derivation of the possible reactions between the stainless steel 304 workpiece and phosphoric acid during laser irradiation and non-irradiation are carried out based on the measured data of XPS, UV-VIS absorption, and ICP-mass, respectively in this paper.

Groove (engineering)

Phosphoric acid

Isotropic etching

10.2961/jlmn.2016.01.0005

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Citations (5)

Fabrication of high-aspect-ratio microgrooves with laser-assisted wet etching for micro heat pipe

Kwang Hwan Oh M.K. Lee Seung‐Hwan Kwon Sungho Jeong

Fabrication of high-aspect-ratio microgrooves with good profile and surface quality is realized using laser-assisted wet etching technique for the application to micro heat pipe.

Aspect ratio (aeronautics)

Dry etching

Isotropic etching

10.1109/cleo.2006.4628599

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Citations (1)

Acoustic Emission Behavior during Fatigue Crack Propagation in 304 Stainless Steel

Key engineering materials (2004)

Kwang Hwan Oh C.K. Jung Yayong Yang Kyung Seop Han

This study investigated acoustic emission behavior during fatigue crack growth test under constant and variable amplitude loading in 304 stainless steel. To describe the acoustic emission behavior, counts rate(dη/dn) was related with stress intensity factor range (SIFR, ΔK) in log-log plot. As a result of test, the relationship was represented a curve, which forms rise and fall behavior in counts rate as the SIFR increases. AE response to a single overload was sudden drop and slow recovery in counts rate, which was similar to crack growth retardation behavior. Under block loading, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental results indicated that stress intensity factor controls the counts rate (dη/dn) as well as crack growth rate (da/dn) regardless of load range or crack length.

Acoustic Emission

Paris' law

10.4028/www.scientific.net/kem.261-263.1325

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Citations (16)