Papers by Author: Young Jin Kim

Abstract: In this paper the fretting wear of press-fitted specimens under partial slip conditions was simulated using finite element method and numerical analysis based on Archard's equation. An elasto-plastic analysis of contact stresses in a press-fitted shaft in contact with a boss was conducted with finite element method and the amount of microslip and contact pressure due to bending load was estimated. The predicted wear profile of press-fitted specimens at the contact edge was compared with the experimental results. It is found that the depth of fretting wear by repeated slip between shaft and boss reaches the maximum value at the contact edge. The initial surface profile is continuously changed by the wear at the contact edge, and then the corresponding contact stresses and strain are redistributed.

Abstract: As the TFT-LCDs are getting more attention for the next generation display device, specifications of the mechanical functionalities of the device is to be more tighter as well as the electrical user specifications. Due to its brittle characteristics of TFT-LCD panels, maintaining mechanical integrity under an impact loading situation is the one of the key design concerns. Furthermore, as the TFT-LCDs are popularly adopted for various mobile equipments such as cellular phones and digital cameras, shock failure of the display should be prohibitive for the design engineers. A major incident being monitored during the shock loading is of course the local material failure of the TFT-LCD panel that might happen at its maximum deformation. The present work delivers a systematic approach for the shockproof design of mobile TFT-LCD. A specially designed shock test setup evaluated by a set of rigorous FEM analyses is shown and comments for the shockproof method is to be also delineated.

Abstract: The present paper provides plastic limit load solutions for axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3-D) finite element (FE) limit analysis using elastic-perfectly plastic behavior. As a loading condition, both single and combined loadings are considered. Being based on detailed 3-D FE limit analysis, the present solutions are believed to be valuable information for structural integrity assessment of cracked pipes.

Abstract: The wall thinning due to erosion, corrosion and flow accelerated corrosion is one of critical issues in nuclear industry. To secure against loss of integrity of pipes with a flaw, ASME Code Section III and Code Case N-597 etc have been used in design and operating stages, respectively. However, despite of their inherent conservatisms, it may reach unanticipated accidents due to degradation at local region. In this paper, a new evaluation scheme is suggested to estimate load-carrying capacities of wall thinned pipes. At first, computational fluid dynamics analyses employing steady-state and incompressible flow are carried out to determine pressure distributions in accordance with conveying fluid. Then, the discriminate pressures are applied as input condition of structural finite element analyses to calculate local stresses at the deepest point. A series of combined analyses were performed for different fluid flow velocities as well as d/t, Rm/t and l/t ratios. The efficiency of proposed scheme was proven from comparison with conventional analyses results and it is recommended to consider the fluid structure interaction effect for exact integrity evaluation.

Abstract: During the past couple of decades, several limit load solutions have been proposed to resolve steam generator (SG) tube integrity issue. However, for estimation of specific load carrying capacity under different conditions, these solutions have to be modified by using lots of experimental data. The objective of this paper is to introduce a new burst pressure estimation scheme based on fracture mechanics analyses for SG tubes with a crack. In this context, closed-form equations were derived to get relevant parameters from three dimensional elastic-plastic finite element analyses and, then, a series of structural integrity analyses were carried out using the predicted J-integrals from the equations. Finally, in comparison with the experimental data as well as corresponding estimation results from conventional limit load solutions, it was proven that the proposed estimation scheme can be used as an efficient tool for integrity evaluation of cracked SG tubes.

Abstract: Railway wheels and axles have been one of the most critical components in a railway vehicle. The service conditions of railway vehicles have became more severe in recent years due to the increase of the speed. It is very important to evaluate the reliability of wheels with regard to safety, because wheel failure can cause derailment with loss of life and property. One of the major reasons of the railway wheel damage is the contact zone failure by wheel/rail contact. One of the methods for preventing the failure and increasing the fatigue life is to grind periodically the contact surface before reaching the failure. The increase or decrease of the contact fatigue life by the surface removal of the contact surface were shown by many researchers. However, the reason why fatigue life increases or decrease has not been investigated obviously. In this study, the effect of the surface removal depth on the contact fatigue life for a railway wheel is evaluated through the employment of rolling contact fatigue tests and the finite element analysis. It is found that the contact fatigue life increased with the removal depth. But in the case that the removal depth is greater than the optimal depth, the contact fatigue life decreased. It seems to be obvious that the residual strain is the main factor determining the fatigue life according to the removal depth

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.

Abstract: 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.

Abstract: Risk-based inspection (RBI) guideline based on API 581 provides a methodology for calculating the risks of equipment in refinery or petrochemical plant. However, there is a major limitation of its application to the petrochemical plant directly since only a representative material is considered in calculating the risk, especially in part of the consequence of failure, even though the equipment is composed of numerous materials. The objectives of this paper are to develop an enhanced RBI program to resolve shortcoming inclusive of the above issue and to evaluate the risks of equipment in petrochemical plant using the program. In this respect, the mole fractions of materials were used to fully incorporate the characteristics of different materials. The proposed RBI program consists of qualitative, semi-quantitative and quantitative risk evaluation modules in which toxic materials as well as representative materials were selected automatically for comparison with those in the current guideline. The RBI program has been applied to evaluate the risks of equipment in Naphtha Cracking Center (NCC) which is a typical facility of petrochemical plant. Thereby, promising evaluation results were obtained and applicability of the proposed RBI program was proven.

Abstract: The heavy load carrying facility, such as ladle crane, is operating under severe working environment. It usually carries melted iron to the furnace, and thus, the accident due to crane failure may cause detrimental damage to the entire steel making factory. While the ladle crane is designed for 20 years of safe operation in a steel making company, several critical cracks due to fatigue loading have been reported during the maintenance process. In order to prevent fatal failure due to crack growth, ladle crane has been periodically inspected and maintained. However, the inspection and maintenance including repair and replacement cause the whole manufacturing line to stop, it is critical to set the appropriate inspection interval and replacement criteria. For this reason, the importance of plant maintenance (PM) has been highly raised to provide efficient plant operation. Recently, a number of engineering methodologies, such as fitness for service guidelines (FFS) and plant lifecycle management (PLM) system, have been applied to improve the plant operation efficiency. Also, a network-based business operation system, which is called ERP (Enterprise Resource Planning), has been introduced in the field of plant maintenance. However, there hasn’t been any attempt to connect engineering methodologies to the ERP PM(Plant Maintenance) system. In this paper, an engineering methodology which provides life time evaluation under fatigue loading has been implemented to the web-based ERP PM system along with real-time fatigue monitoring system. In order to monitor the real time loading, a web-based fatigue monitoring system for ladle crane has been developed and installed inside the ladle crane. For the estimation of fatigue life, 3-dimensional finite element (FE) analyses were conducted for actual transients. Finally, the fatigue life time estimation program is developed by integrating FE analysis results and real-time monitoring data. For the direct calculation of remained fatigue life, an artificial neural network (ANN) algorithm has been applied. The proposed system is expected to play a great role in determining appropriate inspection and maintenance schedule which has become critical issue for the efficient plant maintenance.