Joon Woo Bae

THREE DIMENSIONAL FINITE ELEMENT SIMULATION OF THE FRETTING WEAR PROBLEMS

The structural integrity of steam generators in nuclear power plants is very much dependent upon the fretting wear characteristics of Inconel 690 U-tubes. In this study, a finite element analysis was used to investigate fretting wear on the secondary side of the steam generator, which arises from flow-induced vibrations (FIV) between the U-tubes and supports or foreign objects. Two-dimensional and three-dimensional finite element analyses were adopted to investigate the fretting wear problems. The purpose of the two-dimensional analysis, which simulated the contact between a punch and a plate, was to demonstrate the validity of using finite element analysis to analyze fretting wear problems. This was achieved by controlling the value of the wear constant and the number of cycles. The two-dimensional solutions obtained from this study were in good agreement with previous results reported by Stromberg. In the three-dimensional finite element analysis, a quarterly symmetric model was used to simulate tubes contacting at right angles. The results of the analyses showed donut-shaped wear along the contacting boundary, which is a typical feature of fretting wear.

EXPERIMENTAL STUDY ON IMPACT FRETTING WEAR OF INCONEL TUBES UNDER HIGH TEMPERATURE AND PRESSURE

In nuclear power plant, fretting wear caused by flow induced vibration (FIV) accompanied with impact force can make serious problems between U-tubes and egg-crates which are located in steam generators. In order to guarantee the reliability of the steam generator, design based on consideration of the damage due to the fretting wear of the U-tube is inevitable. The purpose of this study is to elucidate fretting wear mechanism qualitatively and quantitatively. First, finite element models are developed to analyze the dynamic characteristics and estimate the impact force in steam generators. Based on the numerical results, fretting wear simulation is performed according to the environment to which the actual steam generators in nuclear power plant are exposed. Initial experimental results are obtained for various experimental parameters and the effect of work rate and temperature on fretting wear is evaluated.

ANALYSIS OF RESIDUAL STRESS FOR NARROW GAP WELDING USING FINITE ELEMENT METHOD

Reactor coolant loop (RCL) pipes circulating the heat generated in a nuclear power plant consist of so large diameter pipes that the installation of these pipes is one of the major construction processes. Conventionally, a shield metal arc welding (SMAW) process has been mainly used in RCL piping installations, which sometimes caused severe deformations, dislocation of main equipments and various other complications due to excessive heat input in welding processes. Hence, automation of the work of welding is required and narrow-gap welding (NGW) process is being reviewed for new nuclear power plants as an alternative method of welding. In this study, transient heat transfer and thermo-elastic-plastic analyses have been performed for the residual stress distribution on the narrow gap weldment of RCL by finite element method under various conditions including surface heat flux and temperature dependent thermo-physical properties.

Analysis of Fretting Problems Using a Numerical Method Based on Cauchy Singular Integral Equation

Numerical analysis by influence function method (IFM) is demonstrated in this study in order to investigate the fretting wear problems on the secondary side of the steam generator, caused by flow induced vibration. Two-dimensional numerical contact model is developed in terms of Cauchy integral equation. The distributions of normal pressures, shear stresses and displacement fields are derived between two contact bodies which have similar elastic properties. The work rate model is adopted to find the wear amounts between two materials. The results are compared with the solutions by finite element analyses, which validates the application of the present method to fretting wear problems.

DEVELOPMENT OF THE HIGH TEMPERATURE FRETTING WEAR SIMULATOR FOR STEAM GENERATOR

In nuclear power plant, fretting wear due to a combination of impact and sliding motions of the U-tubes against the supports and/or foreign objects caused by flow induced vibration, can make a serious problem in steam generator. A test rig, fretting wear simulator, is developed to elucidate fretting wear mechanism qualitatively and quantitatively. The realistic condition of steam generator of high temperature up to 320°C, high pressure up to 15 MPa, and water environment could be achieved by a test rig. The fretting wear simulator consists of main frame, water loop system, and control unit. Actual contact region under a realistic condition of steam generator was isolated using autoclave. Effects of various parameters such as the amounts of impact and sliding motions, applied loads and initial gaps and so forth are considered in this research. After the experiment, wear damage was measured by a three-dimensional profiler and the surface was also studied by SEM microscopically. Initial results were also presented.

Heparinized Tissue Matrices as Novel Biomaterials

Novel approaches using bioactive molecules in the purpose for overcoming the limitation of established materials have been studied. Their ultimate goal is focused on improved blood/cell compatible biomaterials for various biomedical applications. Heparin-bound bioactive materials using bovine pericardium have been developed. From results of heparinized cellular or acellular tissue matrices, the effect of heparin on the tissue in cell-related biological responses as well as improved blood compatibility was confirmed. These heparinized matrices can be useful for tissue regeneration through the control of growth factor in tissue engineering as well as cardiovascular application. Introduction The extensive research has been performed in the design of new polymers for a variety of medical devices and biomedical applications. Great progress in artificial organs, prosthetic devices, and medical diagnostics can be attributed to these scientific advances in biomedical polymers. Although a substantial amount of work in the blood/tissue compatible polymers has been carried out, the results are still inconclusive. This is caused partly by the fact that the relationships between surface properties and blood and cell interactions have not been thoroughly evaluated. A variety of approaches have been taken to improve the blood/tissue compatibility of biomaterials surfaces. Approaches involve: (a) physical coating of polymer, (b) surface modification by grafting hydrophilic component such as poly(ethylene oxide) (PEO) and incorporating bioactive agents such as potent anticoagulant (heparin) and cell adhesive molecules through either physical or chemical coupling, and (c) biological modification using protein or cell seeding. Heparin, a well-known polysaccharide as a representative anticoagulant can modulate the bioactivity of heparin binding growth factor and cell-related cytokines through different mechanisms. Therefore, the development of surface modification techniques using heparin can have great advantages for the design of blood/tissue compatible biomaterials. In our laboratory, various approaches to improved biocompatibility of biomaterials using heparin have been studied. In this paper biological tissues having heparin will be discussed in detail. Cellular and acellular matrices of bovine pericardium (BP, ABP, respectively)) were chemically modified by simple direct coupling of heparin. Materials & Methods Key Engineering Materials Online: 2005-06-15 ISSN: 1662-9795, Vols. 288-289, pp 453-456 doi:10.4028/www.scientific.net/KEM.288-289.453