Materials Science Forum Vols. 580-582

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https://doi.org/10.4028/www.scientific.net/MSF.580-582

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Paper Title Page

Characterization of Weldments and Materials Using Thermoelectric Power Measurements

Authors: Young Do Park, A.N. Lasseigne-Jackson, J.E. Jackson, Brajendra Mishra, D.L. Olson, T. Koenig

Abstract: Thermoelectric power coefficient measurement techniques have been developed for numerous applications to guarantee material integrity by providing a non-destructive electronic property correlation to material microstructure, phase stability, specific solute additions, and lattice strain. How the electron concentration, the effective mass, and the dominating scattering mechanisms allow for non-destructive evaluation of materials will be described. Because thermoelectric power (TEP) is dependent upon numerous variables, additional non-destructive techniques are necessary to further characterize or classify the material or weldment. The concept of an electronic metallography laboratory is developed using additional collaborative NDE technologies.

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Application of Air-Coupled Ultrasonic Techniques Using Carbon/Carbon Composites

Authors: In Young Yang, Yong Jun Yang, Jun Woo Park, Kil Sung Lee, Young Tae Cho, Je Woong Park, David K. Hsu, Kwang Hee Im

Abstract: Carbon/carbon(C/C) composite materials have obvious advantages over conventional materials, which consist of carbon fibers embedded in a carbon matrix. It’s low density, high thermal conductivity and excellent mechanical properties at elevated temperatures make it an ideal material for aerospace applications especially aircraft brake disks. Because of permeation of coupling medium such as water, it is desirable to perform contact-less nondestructive evaluation to assess material properties and part homogeneity. In this work, a C/C composite material was characterized with non-contact and contact ultrasonic methods using automated acquisition scanner. . Due to the acoustic impedance mismatch found between most materials and air, a major limitation for air-coupled transducers, through-transmission mode was performed. Especially ultrasonic images and velocities for C/C composite disk brake were measured and found to be consistent to some degree with the non-contact and contact ultrasonic measurement methods. 400 kHz frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the inhomogeneity in material property. Non-contact measured results were compared with those obtained by the motorized system using contact drycoupling ultrasonics and through transmission method in immersion. Results using a proposed peak-delay measurement non-contact method corresponded well to the ultrasonic velocities of the contact pulse overlap method.

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J-Integral Estimation for the 3-D Through-Thickness Centre-Cracks in Welds of Structural Steels

Authors: Chin Hyung Lee, Kyong Ho Chang

Abstract: For the fracture analysis of a crack in welds, residual stress analysis and fracture mechanics analysis must be performed sequentially. In this study, characteristics of residual stresses in welds of structural steels (SM490, SM520, SM570) were presented by carrying out three-dimensional (3-D) thermal elastic-plastic finite element (FE) analysis. Then, an FE analysis method which was able to calculate domain-independent values of the J-integral for a crack in a 3-D residual stress bearing body was developed to evaluate the J-integral for a mode-I centre-crack in welds of structural steels when mechanical stresses were applied in conjunction with residual stresses. The results show that the longitudinal residual stresses in welds increase with increasing yield stress of the welded steel (SM490

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New Technology for NDT Weld Inspections – Phased Arrays and Diffraction Sizing

Authors: Simon Labbé, Michael Moles

Abstract: This article describes new techniques and technology for inspecting welds using automated ultrasonics. The prime new technology is phased arrays, while the new techniques are Time-of-Flight Diffraction and S-scan back diffraction. The relationship of phased arrays with North American codes is briefly given, along with an inspection result, comparing radiography, pulse-echo phased arrays and TOFD.

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Implementation Status of Performance Demonstration for Nuclear Power Plant Piping Weld Ultrasonic Examination in Korea

Authors: Yong Sik Kim, Hee Jong Lee, Se Kyoung Kim

Abstract: The ASME B&PV code section XI adopted the performance demonstration requirements (Appendix VIII) for the ultrasonic examination of nuclear power plant piping weld in the 1989 winter addenda for the first time. Korea Electric Power Research Institute(KEPRI) and Korea Hydro and Nuclear Power Company(KHNP) finished developing Korean Performance Demonstration(KPD) system for the ultrasonic examination to apply pressurized light-water and pressurized heavy-water reactor power plants piping weld in accordance with ASME code section XI, appendix VIII on January 2004. KEPRI has been accomplishing the performance demonstration for nuclear power plant piping weld ultrasonic examination in Korea from April 2004. This paper describes the implementation status of the performance demonstration for nuclear power plant piping weld ultrasonic examination in Korea.

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Analysis on Thermal Strain of AC7A Aluminum Alloy Casting Mold for Automobile Tire by Finite Element Method

Authors: Je Se Choi, Yool Kwon Oh

Abstract: In the present study, AC7A aluminum alloy casting mold which consist of 8 pieces is introduced as an analysis model. Also, numerical work using a finite element method was applied to investigate the thermal strain that included the temperature distribution, stress and strain during the cooling process in AC7A casting mold. In addition, the numerical work was carried out that analysis results of the AC7A casting mold were compared with those of mild steel casting mold to prove the improvement and good quality. The numerical results such as temperature distributions, stress and strain are presented to help to make the effective and the best tire mold. In addition, the introduced technique of numerical work using a finite element method is very useful and especially needs to improve the precision of tire mold such as sectional type or puzzle type.

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A Numerical Study on Nonequilibrium Heat Transfer and Crater Formation in Thin Metal Films Irradiated by Femtosecond Pulse Laser

Authors: H.S. Sim, K.G. Kang, Seong Hyuk Lee, Jong Min Kim, Young Eui Shin

Abstract: The ultimate goals of this study are to investigate numerically nonequilibrium energy transfer between electrons and phonons, and to predict the crater formation shapes of gold thin film structures irradiated by femtosecond pulse lasers. In particular, the present article expands the onedimensional two-temperature model (1DTTM) to the two-dimensional model (2DTTM) considering wave interference, and it involves the quantum effect to predict thermal and optical properties. The predictions by using 2DTTM are extensively compared with those of 1DTTM, and the influence of film thickness on radiation heat transfer and optical characteristics are also examined. From the results, it is found that the predictions of 2DTTM are in good agreement with those of 1DTTM. As the gold film thickness decreases, the reflectivity decreases dramatically and the absorbed laser intensities at the top surface increases substantially because of wave interference in thin films.

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Determination of Optimum LASER Welding Parameters and the Development of a LASER Welding Technique to Enhance the Lateral Impact Strength of a Spacer Grid Assembly for a PWR Fuel Assembly

Authors: Kee Nam Song, Soo Sung Kim

Abstract: A spacer grid assembly, which is an interconnected array of slotted grid straps welded at the intersections to form an egg crate structure, is one of the core structural components of the nuclear fuel assemblies of a Pressurized light Water Reactor (PWR). The spacer grid assembly is structurally required to have enough buckling strength under lateral loads so that the nuclear fuel rods are maintained in a coolable geometry, and that control rods are able to be inserted. The ability of a spacer grid assembly to resist lateral loads is usually characterized in terms of its dynamic and static crush strengths. Since the crush strengths of a spacer grid assembly are known to depend on the weld qualities at the intersections of the slotted grid straps, high-tech welding methods, such as a TIG welding, LASER beam welding or Electron beam welding method, have been used recently in the nuclear fuel manufacturing fields. In this study, to meet the above requirements, two kinds of researches were carried out. First, by adjusting the LASER beam welding parameters, an optimum welding combination of the LASER beam welding parameters was obtained for welding a spacer grid assembly. Second, a new LASER beam welding technique was proposed to obtain a longer weld line and a smaller weld bead size by tilting the LASER beam. The buckling strength of the spacer grid welded by the new LASER beam welding technique was enhanced by up to 30 % when compared to that by the conventional LASER beam welding method.

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Effect of Micro Structure in Fuel Cell Electrode on Concentration of Species in Reaction Layer

Authors: Masahiko Sugimura, Kiyokazu Yasuda, Michiya Matsushima, Kozo Fujimoto

Abstract: Fuel cell is one of the promising candidates for mobile power source. In the fuel cell, the design considering micro structure is considered to be indispensable for developing a highperformance cell. In this work, the effect of the anode electrode structural design of the DMFC (direct methanol fuel cell) on the cell performance was investigated by three-dimensional numerical simulation. The influence of diffusion layer thickness in the electrode on the mass fraction of methanol and carbon dioxide in the reaction layer is examined for various operation conditions. As a result, we clarified that the micro structure change in the electrode significantly affected the mass fraction of the species in reaction layer in the fuel cell.

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A Brief Review of Challenges & Technologies to Weld Dissimilar Metals in Two Industries: The Upstream Oil & Gas and the Automotive

Authors: Manuel Marya

Abstract: In both Oil & Gas (OG) and automotive industries, welding is an essential part of fabrication routes and the challenges in welding metallic materials are frequently similar. Processes that are fast, robust, and therefore tolerate variations in process parameters (including operators for manual processes) and materials (i.e. compositions and properties) are important to reproduce high weld quality and facilitate non-destructive examinations (NDE). New grades of high-strength alloys, required to be weldable by common processes and preferably without post-weld heat treatments, are not only needed by both industries, but dissimilar-metal welding is also becoming unavoidable, thereby demanding for novel processes with either low heat inputs or high-energy densities. In this paper, technologies for dissimilar-metal welding are examined in reference with both OG and automotive applications.

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