Papers by Author: Tae Won Kim

Abstract: Physical vapor deposition technique has been employed to develop a thin film of OLED, and atomic force microscopy was used to investigate the boundary characteristics such as uniformity of emitting layer, roughness, and surface morphology. In order to determine the deposition characteristic which associated with the materials failure in OLED, finite element simulation, together with alternative analytical modeling has been carried out by means of island growth mechanism analysis. The boundary growth of thin film can be determined from the velocity of island boundary using simple rate equations. The results obtained are compared with experimental observation. Generally good agreement has been achieved.

Abstract: A stochastic approach has been presented for superplastic deformation of Ti-6Al-4V alloy, and probability functions are used to model the heterogeneous phase distributions. Experimentally observed spatial correlation functions are developed, and microstructural evolutions together with superplastic deformation behavior have been investigated by means of the probability functions. The strain-rate dependent failure strain can be correctly predicted by the model. As shown by the results the probability varies approximately linearly with separation distance, and significant deformation enhanced probability changes occur during the process. Since an initial microstructure is the most crucial factor that determines the properties of final microstructure, Monte Carlo simulation has been used coupled with the probability functions for the reconstruction of microstructures. By imposing the precisely optimized distributions of phase on the test specimens, therefore finite element implementation shows better agreement with experimental data of the failure strain.

Abstract: OLED has many advantages such as possibility to make micro size, tiny driving power, and fast response time with high resolution. However, significant commercial level problems are being recognized resulting from the damage of emitting layer, degradation of organic layers, and generation of dark spot. It is therefore necessary to overcome the problems for the development of high performance products. Deposition characteristic associated with the materials failure in OLED has been determined, firstly, by means of the analysis of the surface morphology and roughness of thin film. Physical vapor deposition technique was employed to develop test specimens, and atomic force microscopy has been used to identify the uniformity of emitting layer. In addition, optimal control set enabling the roughness of thin film surface to be minimized is presented, and the results obtained are compared with the experimental data. Generally good agreement has been achieved. It is known that the luminance decay mechanisms are directly related to the reliability of finished products, and thus further investigation has been carried out using the luminance decay curves. As shown by the results, the luminance decay may be divided into two major components during the failure processes. One is simple exponential during operation and the other is rapid decline in the initial stages of operation. It can be thought that the simple exponential decline is related to a chemical degradation of Hole Transport Layer, whereas the rapid decline is probably due to the generation of an internal electric field.

Abstract: Rubber-modified epoxy resins are used as a matrix material for glass and carbon-fiber composites. Mechanical properties of fiber reinforced composites depend on the interfacial shear strength between the reinforced fiber and the matrix resin. This study is focused on the interfacial shear strength in the reinforced carbon fiber and rubber-modified epoxy resin system. To evaluate interfacial shear strength between the fiber and the resin, pull-out test is performed using a microdroplet method. Based on experimental results, numerical analysis was also simulated. It is concluded that the interfacial shear strength of carbon fiber/unmodified epoxy resin system was higher than that of carbon fiber/modified epoxy resin system. The reason for decreased the interfacial shear strength of rubber-modified system is that contractive forces in neat epoxy resin acting on carbon fiber were less than those in rubber-modified epoxy resin system.