Seong In Moon

Determination of equivalent single crack based on coalescence criterion of collinear axial cracks

In a nuclear power plant the steam generator tubes cover a major portion of the primary pressure-retaining boundary. Thus, very conservative approaches have been taken in the light of steam generator tube integrity. According to the present criteria, tubes wall-thinned in excess of 40% should be plugged whatever the cause. However, many analytical and experimental results have shown that no safety problems exist even with thickness reductions greater than 40%. The present criterion was developed about 20 years ago when wear and pitting were dominant causes for steam generator tube degradation, and it is based on tubes with single cracks regardless of the fact that the appearance of multiple cracks is more common in general. The objective of this study is to review the conservatism of the present plugging criteria of steam generator tubes and to propose a new coalescence model for two adjacent through-wall cracks existing in steam generator tubes. Using the existing failure models and experimental results, we reviewed the conservatism of the present plugging criteria. In order to verify the usefulness of the proposed new coalescence model, we performed finite element analysis and some parametric studies. Then, we developed a coalescence evaluation diagram.

Investigation on the interaction effect of two parallel axial through-wall cracks existing in steam generator tube

It is commonly required that steam generator tubes wall-thinned in excess of 40% should be plugged. However, the plugging criterion is known to be too conservative for some locations and types of defects and its application is confined to a single crack. In the previous study, the conservatism of the present plugging criterion of steam generator tubes was reviewed and a crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed. Since parallel axial cracks are more frequently detected during in-service inspections than collinear axial cracks, the studies on parallel axial cracks spaced in circumferential direction are necessary. The objective of this paper is to investigate the interaction effect between two parallel axial through-wall cracks existing in a steam generator tube. Finite element analyses were performed and a new failure model of the steam generator tube with these types of cracks is suggested. Interaction effects between two adjacent cracks were investigated to explain the deformation behavior of cracked tubes.

Synthesis and Electrochemical Study of Zr-Doped LiNixMnyCo(1-x–y)O2 as Cathode Material for Secondary Li-Ion Battery

In this work, a simple way was contrived to enhance the rate capability and cycle life of LiNixMnyCo(1-x-y)O2 by doping Zr into the material. Zr-doped LiNixMnyCo(1-x-y)O2 was synthesized by solution-based synthetic route, and its electrochemical performance was investigated as 2016 coin-type half cell. With doping, some impurity peaks appeared in the XRD pattern, which seems to be related to Zr containing oxides. The enhanced characteristics in the rate capability and cycle life might be the result of the protective effect of Zr oxide against the decomposition of electrolyte and a faster Li diffusion rate.

Simplified impact analysis based on equivalent static analysis for impact design of TFT-LCD panels

This paper presents a new computational approach to simulate impact response of a large TFT-LCD panel. The approach is based on the static load analysis equivalent to impact analysis. The static problem equivalent to the impact one is found from the concept of solid mechanics to estimate the maximum deflection and stress. To show the plausibility of the proposed approach, it is applied to a simple, idealized problem, a beam subject to impact loading. Based on explicit FE analyses using the LS-DYNA FE program, time variation of energy within the beam is investigated systematically, from which the steady state internal energy stored in the beam and the maximum stress are characterized in terms of the shock duration. Noting that the maximum stress is related to the internal energy, an equivalent static problem to the impact problem is found by equating the strain energy to the internal energy. Comparison of the maximum stress for the equivalent static problem with that for the impact problem shows that the ratio can be uniquely characterized by the shock duration, and moreover varies slightly, from 1.2 to 1.0, which suggests that the impact problem can be solved by the equivalent static analysis which is much easier to solve in practice. Thus the proposed approach provides significant advantages in design optimization of a large TFT-LCD monitor against chock failure, and enables the designer to avoid ad hoc modeling of the transient dynamics so that product design cycle could be shortened. Introduction As the TFT-LCD (Liquid Crystal Display) gets more attention for the next generation display device, the user requirements for the mechanical functionalities as well as the electrical user specifications for the device become much tighter. Due to its brittle characteristics of TFT-LCD panels, maintaining mechanical integrity under severe impact loading is one of the key design concerns. For instance, shock failure of electronic devices during either the manufacturing or shipping processes has been an increasing burden of production cost especially for a large panel of 40 inches size or larger, that are now mainly used for TV sets. A major concern during the shock loading is of course the local material failure of the TFT-LCD panel [1]. A typical design-supporting tool against failure under impact loading is detailed impact simulation based on the Lagrangian FE analysis with the explicit integration scheme [1-3]. Despite its popularity, such impact analyses still suffer from several problems. For instance, compared to static analysis, the accuracy of results depends on computational algorithm employed in the analysis [2]. Moreover, impact analysis typically requires tight convergence control, which limits freedom of mesh generation, as the convergence criterion depends on the smallest mesh size [1]. As results, impact analysis typically requires both enormous human interactions in modeling and computational costs. As competitive market needs the shorter cycle for product design, the use of the impact simulation to optimum design against shock failure is getting All correspondances are to be sent to Professor Koo at jckoo@skku.edu, Fax: +82-31-290-7916 Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 114-119 doi:10.4028/www.scientific.net/KEM.270-273.114

A Development of Optimization Tool for Mechanical Shock Proof Design of a Digital Display Panel

Because of the harsh user environment of Lap-Top (Notebook) PCs, developing rugged components and assembly is to be one of the major interests in the industry. User requirements for the reliability of the PCs have been rapidly raised as the market grows. Especially mechanical shock failures of a display unit of those PC kinds have been an important concern of designers. Brittle and non-homogeneous material characteristics of the thin TFT-LCD display panel have hampered to make a reliable design strategy to meet the tightening shock user specification. In order to satisfy the requirement, many different design cases should be elaborated in both numerical simulations and proto-typings prior to the volume production that usually consist of tedious time consuming processes. As compared the life cycle of the fast changing product, the reduction of design processes gets tremendous attention from not only PC designers but LCD makers. In order to achieve the mechanical shock requirement of a couple of hundred times of gravitation, an explicit Lagrangian FE model is being used as a major analysis tool. Since the nature of the explicit formulation and the relatively large deformation of thin parts in a LCD panel, the FE model should be carefully built especially in terms of element distribution. Otherwise the analysis could be very expensive either by the lengthy computation or the singularity occurring in middle of the calculation. Meanwhile, the LCD display manufacturers often have many production models similar in exterior shape but different in construction for the various customers. Each different construction may perform differently under the same mechanical shock loading. This paper presents an optimization tool for the shock-proof design of notebook TFT-LCDs. Constructing geometries of the key design features, generating proper meshes for the entire display unit, cranking up an explicit FE codes, and analyzing the results are combined in a unified tool with user friendly features. A good agreement to the prototyping test also has been shown using a design example.

Assessment of steam generator tubes with dual axial through-wall cracks

In this paper, conservatisms of current plugging criteria on steam generator tubes are reviewed and six new failure prediction models for dual through-wall cracks are proposed. In order to determine the optimum ones among these local or global failure prediction models, a series of plastic collapse tests and corresponding finite element analyses are carried out with respect to two adjacent axial through-wall cracks in thin plates. Then, reaction force model, plastic zone contact model and COD (Crack Opening Displacement) base model were selected as the optimum ones for integrity assessment of steam generator tubes with dual cracks.

Simplified Static Analysis for Shock Behavior Evaluation of Thin Glass Plates

Recently, mechanical shock failures of a flat display unit such as TFT-LCD device have been an important concern of designers. In order to achieve the mechanical shock requirement, it is necessary to perform the detailed FE analyses which could be very expensive either by the lengthy computation or by the complicated geometry modeling. The objective of this study is to propose a simplified analysis methodology to simulate impact behavior of thin glass plates. The static problem equivalent to the impact one is found from the concept of solid mechanics to estimate the maximum deflection and stress under impact loading. To show the plausibility of the proposed approach, it is applied to the idealized problem which is a two dimensional beam subjected to impact loading. Based on explicit FE analyses using the LS-DYNA FE program, it was shown that the impact problem can be solved by the equivalent static analysis which is much easier to solve in practice. Therefore, the proposed approach provides significant advantages in design optimization of a TFT-LCD device against shock failure, and enables the designer to avoid ad hoc modeling of the transient dynamics so that product design cycle could be shortened.

An Effective Method for Measuring Elastic Modulus of Large TFT-LCD Panels

Measurement of mechanical properties of a thin large crystallized material such as TFT-LCD panel is challenging with traditional material testing equipments. Since TFT-LCDs are constructed with combination of brittle glass panels, polymer sheets, and liquid crystal, their properties are not only anisotropic but also usually non-linear. Accurate measurement of the properties often requires very expensive facilities. Especially when the size of the test sample is as large as 40-inch or wider, direct measurement cost of even elastic modulus is prohibitive. On the other hand, machining of the large TFT-LCD to make a smaller size specimen that could be fit into a material tester is not possible due to leaking liquid crystal. A new method for the measurement of elastic modulus of large TFT-LCD panel is presented in this article. The suggested method provides a simple, economic, and user-friendly way for measuring the elastic modulus of large panels with considerable level of accuracy. The measured elastic modulus is verified by the combination of part level modal test and analysis, and impact test and analysis at the assembled digital TV level.