Papers by Author: Jung I. Song

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Authors: Yi Qi Wang, W.K. Joo, Chae Sil Kim, Jung I. Song
Abstract: High-temperature oxidation resistance of 7 wt.%Y2O3-ZrO2 thermal barrier coatings (TBCs) irradiated by high-intensity pulsed ion beam (HIPIB) has been investigated in a cyclic oxidation condition at 1050 °C ×1 h. The ceramic coating of a tetragonal ZrO2 phase structure was prepared on GH33 superalloy substrates with a NiCoCrAlY bond coat by using electron-beam physical-vapor deposition (EB-PVD). The ceramic coating is composed of columnar grains forming dense clusters spacing with several-μm gaps among grain clusters. The characteristics of the columnar grains disappeared after HIPIB irradiation at the ion current densities of 100-200 A/cm2, and the irradiated surface presented a smoothed, densified feature after the remelting and ablation due to the HIPIB irradiation. The thickness of the densified layer is about 1 μm. After oxidation with 15 cycles at 1050 °C ×1 h, the oxidation kinetics curves of the as-deposited and irradiated TBCs showed a parabolic shape. The weight gain of original sample is about 0.8-0.9 mg/cm2, while the values of the HIPIB-irradiated TBCs decreased to some extent. The lowest weight gain is obtained for the irradiated TBCs at 200 A/cm2 with one shot, being 0.3-0.4 mg/cm2, and those at 100 A/cm2 have a medium weight gain of 0.6-0.7 mg/cm2. The cross-sectional morphologies of HIPIB-irradiated TBCs show less oxidation of the NiCoCrAlY bonding layer, with a thinner thermally grown oxide (TGO) layer. The morphology observation is consistent with the results of cyclic oxidation test. It is found that the inward diffusion of oxygen through TBCs can be significantly impeded by the densified top layer by the HIPIB irradiation, thus limiting the oxidation of the bonding layer, improving the overall oxidation resistance of the irradiated TBCs.
Authors: Byung Il Kim, Byeong Wook Noh, Young Woo Choi, Sung In Bae, Jung I. Song
Abstract: Impact behaviors of Aluminum Honeycombs Sandwich Panel (AHSP) by drop weight test were investigated in this study. Two types of specimens with l/2" and l/4" cell size were tested by two impactors with the weight of 5.25kgf and 11.9kgf respectively. Transient, contact and elastic-plastic analyses were performed by finite element method. Impact behavior of AHSP about impact sites appeared nearly the same in low impact energy, but it was different in high impact energy. Face was the strongest about impact and short-edge was the weakest. The damaged area of AHSP was enlarged with the increase of impactor weight that is corresponding to impact energy. After 3-point bending test, fracture modes of AHSP were analyzed with AE counts, lower face sheet was fractured in the long-edge direction first, and then separation between face sheet and core happened. In the short-edge direction after core wrinkled, lower face sheet was torn, impact behavior by FE analysis were increased localized damage in high velocity because the faster velocity of the impact was, the smaller the stress of core was. Consequently, impactor weight had an effect on widely damaged area, while the impact velocity gave rise to localized damaged area.
Authors: Jeong Seok Oh, Jun Komotori, Jung I. Song, Tae Gyu Kim
Abstract: Rotational bending fatigue tests were carried out on a medium carbon steel with a thermally sprayed Co-based alloy coating. The effect of two different fusing treatments on the fatigue strength of fused specimens was investigated. Fusing treatment was performed using a vacuum furnace, and an induction heating system. When the specimens were treated in vacuum furnace at 1373 K for 4 h, the diffusion layer providing a strong adhesive force were formed at the interface between the coating and substrate. As a result, fatigue strength remarkably increased in comparison with the uncoated specimens. On the contrary, for the treated specimens with an induction heating system at 1373 K for 120 s, since these specimens had a lower adhesive force due to no formation of diffusion layer, leading to delamination of the entire coating.
Authors: Sheikh Md. Rasel, Foisal Ahmed Mirza, Ali Md. Afsar, Jung I. Song
Abstract: The main objective of this study is to examine the two dimensional surface crack problems in a system with an interface between two elastic-plastic solids of different yield strength subjected to mode I mechanical loading. The surface cracks growth is considered to occure along the interface direction of bimaterials which is perfectly bonded to each others. A two dimensional finite elementmethod is used to solve the structural problem. Solid 183-node elements are utilized to simulate the strain singularity around the crack front. The crack surface is subjected to a compressive load by three point bending. The stress intesity factors are computed by using the displacement correlation technique. The primary goal is to develop a model crack tip stresses and strains in a manner that is useful for crack growth initiation and propagation in a FGM.
Authors: W.K. Joo, Yi Qi Wang, H.T. Yang, W.C. Lee, C.Y. Sim, Jung I. Song
Abstract: The microstructures and mechanical properties of OFHC copper/STKM 11A for D-tube joints brazed using BAg filler metal at 870 °C for 20 minutes in NH3 atmospheres were performed. Interfacial microstructures were observed in reaction layer. A brazing strength causes of decline with defects of pin hole and base metal by lack of penetration. In tensile test, the properties of joints clearance of 0.01mm are better than other joints clearance that has yield strength of elasticity area with the brazing length of 2.5mm, and also suitable for the case of brazing length of 5.0mm. According to the results of FEA (finite element analysis) on the tensile test, the maximum stress and strain were generated apart from the interface in large deformation. Diffused layer was formed by counter diffusion action of base metal and filler metal layer, and crack between two base metals was not discovered. This is the main reason that fracture of test piece does not appear in copper base metal, and brazing department forms good junctures.
Authors: Byeong Wook Noh, Young Woo Choi, Jung I. Song, Sung In Bae
Abstract: The Combine is necessary equipment in the agricultural industry. The components of the Combine are worked for a long time under inferior environmental condition. Especially reaping knife is worked in high frequency domain, and submit fatigue load while use. So, fatigue test was performed to obtain the S-N curve of real component, and load history is measured through field test. The local stresses due to these loads have been calculated by FEM. These results have been used as the input values for the multi-axial fatigue analysis of real components. For the assessment of multi-axial fatigue damage, the critical plane methods have been employed. The used parameters of critical plane methods are Morrow’s, Smith-Waston-Topper’s, and Brown-Miller’s, those were modified for the high cycle fatigue region within elastic behavior. In addition, design improvement is performed about shape of reaping knife to increase the endurance limit, and durability test for improved knife is performed. It is found that the fatigue life of improved reaping knife is increased, and durability test result show that life of reaping knife is increased enough.
Authors: Young Woo Choi, Byeong Wook Noh, Jung I. Song, Sung In Bae
Abstract: The fatigue life of hexagon head and socket head bolts, attached to vehicle a wheel, is assessed and the estimation of the residual life of existing bolts in vehicle wheel is investigated. Fieldmeasured load histories were applied in this test. Tensile tests and fatigue tests were performed to evaluate the effect of tightening torque and to obtain the basic experimental data. Miner’s rule was used to predict the fatigue life of bolts. The results indicate the prediction of fatigue life of the bolts was in good agreement with the real life of vehicle wheel bolts in this test.
Authors: Byeong Wook Noh, Jung I. Song, Sung In Bae
Abstract: In this study, fatigue strength of load-carrying cruciform fillet welded joints were evaluated using a new method proposed by Yamada, for geometric or structural stress in welded joint, that is, one-millimeter stress below the surface in the direction corresponding to the expected crack path. Validity of the method is verified by analyzing fatigue test results for load-carrying cruciform welded specimens has different size of weld toe radius, leg length and plate thickness reported in literature. Structural stress concentration factor for 1mm below the surface was calculated by finite element analysis for each specimen respectively. When compared to the basic fatigue resistance curve offered by BS7608, the one-millimeter stress method shows conservative evaluation for load-carrying cruciform fillet welded joints.
Authors: Foisal Ahmed Mirza, Sheikh Md. Rasel, Myung Soo Kim, Ali Md. Afsar, Byung Sun Kim, Jung I. Song
Abstract: Composites with polypropylene (PP) and lyocell fibers were manufactured by compression molding technique. In order to improve the interfacial adhesion between the natural fibers and thermoplastic matrix during manufacturing, maleic anhydride grafted polypropylene (MAPP) as a coupling agent has been employed. Physical properties such as void contents and water absorption rate were studied. Tensile and flexural tests were carried out to evaluate the composite mechanical properties. Tensile test results showed the higher strength and modulus of composite than pure polypropylene (PP). In addition, strength and modulus were found to be influenced by the variation of MAPP contents (1%, 2%). Unlike tensile properties, flexural properties were not improved. However, between 1 and 2 wt% MAPP content, the composites containing 2 wt % MAPP showed better flexural properties than 1 wt % MAPP.
Authors: W.K. Joo, B.I. Kim, Sung In Bae, Chae Sil Kim, Jung I. Song
Abstract: The mechanical properties of bone have been found varying at different structural levels. The different mechanical properties might indicate some important information, such as the ultrastructure of various bone tissue. Descriptions of the structural features of bone are intensive in current studies. However, the mechanical properties of bone, in particular those at the micro-and nanostructural level (material level) remain poorly understood. To probe the mechanical properties at the microstuctural level, the nanoindentation technique is applied. Nanoindentation as a promising technique is widely used in the materials science community for probing the mechanical properties of thin films, small volumes, and small microstructural features. Nanoindentation has been shown to be an effective method to probe the mechanical properties of microstructures at the micron scale.
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