Papers by Author: Noh Yu Kim

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Authors: Min Sung Hong, Jong Min Kim, Noh Yu Kim
Abstract: Electron beam welding (EBW) has an important role in industrial applications such as semi-conductor and LCD manufactures because of its high performance and accuracy. Since the operation is done in a vacuum room, it is very difficult to test the weldability as well as the correct welding area of the specimen. In this study, a measurement system of the EBW was developed based on the 3-axis LVDT controlled table. In addition, the algorithm to tracking the welding line has been developed. The weldability of the aluminum specimen was tested by a newly developed measurement system with ultrasonic C-scan inspection.
Authors: Noh Yu Kim, Sung Young
Abstract: In this work, finite element calculations were carried out to simulate wire pullout process of the shape memory alloy (SMA) wire/carbon fiber reinforced polymer (CFRP) hybrid composite. Three-dimensional cohesive zone model was used for the bonding interface between the SMA and the CFRP. Phase transformation behavior of the SMA wire was accounted for by using a multi-variant constitutive model. The numerical parameters were fitted using an experimental measurement reported by Jang and Kishi. Young’s modulus of the wire affected the force vs. elongation curve most effectively. It is shown that the actual shear stress profile is not constant but it varies significantly along the axial direction of the wire. Additional toughness due to the SMA wire was higher than the case of a purely elastic wire, and the toughness increment was approximately 21 kJ/m2. This value is comparable to the typical toughness value of CFRP.
Authors: Sang Soon Lee, Noh Yu Kim
Abstract: In this paper, the boundary element analysis of viscoelastic strain energy release rate ) (t G for the cracked linear viscoelastic solids has been attempted. The ) (t G has been defined as the derivative of the viscoelastic potential energy ) (t P with respect to crack length a . Numerical results show the applicability of the proposed method to the analysis of the cracked linear viscoelastic structures.
Authors: Noh Yu Kim, Hwan Seon Nah, Sang Soon Lee
Abstract: In order to evaluate the degradation of the epoxy coating in nuclear power plants, acoustic wave velocities of epoxy films are measured using defocused scanning acoustic microscopy system(SAM). Unlike metals, the surface of the epoxy coating on the concrete liner is so thin and wavy that the conventional ultrasonic techniques for acoustic velocity of epoxy coating are hard to apply. Acoustic velocities of bulk waves are determined from V(z,t) curves of mode-converted waves generated in the film by SAM. Epoxy films are fabricated and degraded under various accelerated aging conditions, and both of longitudinal and shear wave velocities of the epoxy film are measured. Approximately 10% of reduction in acoustic wave velocity is observed from experimental results when the aging is developed fully in epoxy films. It is also found that longitudinal wave is more sensitive to deterioration of epoxy coating than transverse wave.
Authors: Noh Yu Kim, Sang Soon Lee
Abstract: Elastic properties of high tension bolt are evaluated non-destructively by measuring acoustic longitudinal and shear wave velocities using mode-converted ultrasound. Mode-converted longitudinal and shear waves along bolt are captured to calculate acoustic wave velocities and determine elastic constants such as Young’s modulus and Bulk modulus based on acoustoelasticity. Ray analysis to select a specific mode conversion from longitudinal mode to shear mode is carried out and discussed with experimental results. From experiment results of maximum 5% of measurement error, it is shown that the proposed mode-converted ultrasonic technique is very effective and sensitive enough to characterize mechanical modulus of high-tension bolts quantitatively.
Authors: Sang Soon Lee, Noh Yu Kim
Abstract: The boundary element analysis is attempted to investigate the relaxation behavior of the bolt load in a single bolted joint fastening thermosetting polymers. More than 10 % relaxation is obtained after 4,000 minutes. The loss of bolt stress is more important because the stress in the polymer is much smaller. Such relaxation of the bolt stress can cause loosening for fasteners and loss of fastener effectiveness for bolts that rely on clamping force or preload to achieve needed joining forces. The experimental evaluation is required to clarify the effect of the loss of bolt load on function of the assembly.
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