Papers by Author: Jae Kyoo Lim

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Authors: Sang Youn Han, Tae Hee Lee, Jae Kyoo Lim
Authors: Ho Chel Yoon, Montasser Dewidar, Jae Kyoo Lim
Abstract: Structure adhesive bonding method is widely used in the industry because it is possible to joint complex shape and dissimilar materials. Especially in the car industry, requests of lightweight car have adhesive bonding method be applied in the many parts. Also it is possible for stress to distribute uniformly through the adhesive layer, and stress concentration is released. Since strength, stiffness durability is much better, this method is determined as the technique replaced weld defect. But, it has much shorter history then other joint method such as spot weld and mechanical joint method. Evaluation of strength and durability is not established. As the fundamental research of design of adhesive bonding joints, considers over-lap length, adhesive thickness, surface treatment and environment which affect strength and durability of single-lap joints. In this research, a real part of bus folding door was used and tested to compare durability of spot welding and adhesive bonding.
Authors: Cong Hoa Vu, Do Won Seo, Jae Kyoo Lim
Abstract: Ductile fracture occurs due to micro-void nucleation, growth and finally coalescence into micro-crack. In this study a new ductile fracture condition that based on the microscopic phenomena of void nucleation, growth and coalescence was proposed. Using this condition and combining with finite element model to predict the fracture locations in bulk metal forming. The macroscopic behavior of the material is described according to the flow rules of Levy-Mises. An idealized spherical void within an finite matrix is assumed. The void volume is calculated by taking the increasing volume of the continuum, caused by plastic straining, incorporated in the yield functions. In the model there includes the strain-hardening coefficient of the Ludwik-Holomom stress-strain relationship and concentration of stress. The accumulated damage value is a phenomenon in this model. The results show that it is in close accordance with observations of some experimental specimens. However, in order to obtaining the high trustiness many experiments have to be carried out.
Authors: Rui Hua Hu, Jae Kyoo Lim, Chul In Kim, Ho Chel Yoon
Abstract: There is an increasing interest in developing fully biodegradable materials for industrial applications. Composite combining biodegradable polymer and natural fiber could be a fully biodegradable material. This work focus on the investigation on China jute fiber reinforced PLA composites. Composites with three different fiber volume fractions were fabricated by film stacking hot press method. Mechanical properties have been investigated and the microstructure of the composites was observed. Fiber surface treatment by silane was applied in order to investigate the effects on the properties of the composites. The moisture absorption rates in a hygrothermal environment were also measured.
Authors: Jin Yi Lee, Ji Seoung Hwang, Se Ho Choi, Jae Kyoo Lim
Abstract: It is important to estimate the intensity distribution of a magnetic field as a possible magnetic method in an industrial nondestructive evaluation application. A magnetic camera provides the distribution of a quantitative magnetic field with homogeneous lift-off and same spatial resolution. Magnetic flux leakage near a crack on the specimen can be amplified by using a 3- dimensional magnetic fluid, that is to say a magnetic lens. This study introduces the experimental consideration of the effects of magnetic lenses for concentrating of magnetic flux. The experimental results showed that the magnetic fluid has a sufficient lens effect for magnetic camera and effect of improvement in probability of detection.
Authors: Jae Kyoo Lim, Seok Yoon Han
Abstract: In order to analyze beam structures more accurately and effectively, a two-node orthotropic beam element is proposed. This beam element is formulated using a consistent higher order deformation theory of orthotropic beams of which the transverse normal deformation can be effectively estimated. The stiffness matrix and the vector of equivalent nodal forces of the beam element are derived explicitly by the Galerkin method. In order to examine the reliability and the characteristics of the beam element, the analytical and the finite element solutions of a simple cantilevered beam are compared with each other. As a result, the following conclusions are obtained; (1) the accuracy of the suggested orthotropic beam element is very excellent and so the transverse normal deformation and shear stress of an orthotropic beam can be effectively estimated. (2) It can be used for accurately analyzing the general beam structures regardless of the Euler's or the Timoshenko's beam.
Authors: Do Won Seo, Yang Bae Jeon, Jae Kyoo Lim
Abstract: Spot welding is a process that sheet metals are joined in one or more spot by heating at the faying interface. In this process, the spatter is dispersed from melted area. It has been reported that spatter generation has adverse effects on weld quality. However, no systematic study has been carried out to find out its effect on weld quality in resistance spot welding processes. In this study, specially designed specimens are used to perform experimental investigation of spatter generation and its effect. Major finding of this study show trends in tensile-shear strength for various amounts of spatter generated during spot welding process. Thus, optimum welding conditions are proposed in view of spatter generation and tensile-shear strength.
Authors: Anil Kunwar, Roma Gurung, Seok Geun Park, Jae Kyoo Lim
Abstract: Green chemistry approach (hydrothermal process) is utilized for grafting maleic anhydride (MA) into linear low density polyethylene (LLDPE), thereby enhancing the compatiblility of the latter in its blend with polylactic acid (PLA). The grafting of MA into LLDPE is confirmed by Fourier Transform-Infrared Spectroscopy (FT-IR) analysis. LLDPE-g-MA content in PLA matrix is varied as 4% wt., 8% wt. and 12% wt. when preparing glass fiber reinforced PLA/LLDPE-g-MA thermoplastic composite via hot pressing. Single Edge Notch Bend (SENB) specimens have been prepared from the composites and three point bend test was performed.The load-displacement plot of the test results indicates that the ductility index (DI) increased for the samples with increased LLDPE-g-MA content. The observation of the fractured surface of specimens in Scanning Electron Microscope (SEM) suggests that the improved DI value is because of the increased matrix ductility owing to the plasticizing effect of the LLDPE-g-MAH inclusion.
Authors: Do Won Seo, Ho Chel Yoon, Yang Bae Jeon, Hyo Jin Kim, Jae Kyoo Lim
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