Papers by Author: Han Ok Ko

Abstract: Fracture toughness data from the cleavage resistance test of structural steels often show a large scatter. Geometry dependency as well as the scatter makes it difficult to evaluate appropriate fracture integrity of cracked components. To address these restrictions, several stochastic models have been proposed by Beremin group, Mudry and other researchers while each of them employs specific estimation scheme and micro-mechanical parameters. The purpose of this paper is to investigate applicability of the Weibull stress model in transition temperature regime and to quantify constraint effect among different-sized CT and PCVN specimens. The constituting parameters m and σu are determined at three temperatures by maximum likelihood estimate (MLE) technique in use of FE analysis results and experimental data of PCVN specimens. Also, failure probabilities of PCVN and CT specimens are calculated from the Weibull parameters, which are used for derivation of a prototype of toughness scale diagram. The diagram provides a technical basis to resolve transferability issue in the same material under different temperatures and constraint conditions.

Abstract: A seamless analysis of IT-related products, such as cellular phone, LCD monitor and note PC etc., which are thin and complex geometry is one of great concerns in product design. However, there is a considerable amount of gap between the industrial application and fundamental academic studies due to a time consuming detailed mesh generation. In order to settle the bottleneck, an auto mesh generation program based on a modified grid-based approach is proposed in this paper. At first, base mesh and skin mesh were generated using informations on entities which extracted from an IGES (Initial Graphics Exchange Specification) file. Secondly, a provisional core mesh with a rough boundary geometry was constructed by superimposing the skin mesh into the base mesh generated from CAD model. And then, positions of boundary nodes were redistributed to delineate exact geometry of the provisional mesh. Finally, good qualified meshes were constructed by moving the positions of the nodes and splitting elements along boundary edges. In conclusion, it is anticipated that the developed program can be used as a promising pre-processor for static or dynamic analysis of various IT-related products.