Effects of frequency on fatigue behavior of type 316 low-carbon, nitrogen-added stainless steel in air and mercury for t
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I. INTRODUCTION
FATIGUE has long been recognized as one of the major causes for the rupture of materials and catastrophic damages in structural components. Fatigue behavior is strongly affected by the environment, and by material and loading conditions.[1] As a candidate target-container material of the spallation neutron source (SNS) being designed and constructed at the Oak Ridge National Laboratory (Oak Ridge, TN), the type 316 low-carbon, nitrogen-added (LN) stainless steel (SS) is required to have good fatigue resistance under severe working environments. The function of the neutron-source system, in which the spallation target is central, is to convert a short-pulsed, highaverage-power 1-GeV proton beam into low-energy, shortpulsed neutron beams optimized for use by neutron-scattering instruments.[2] The main work in the materials research and development (R&D) program for the neutron-source system covers the mercury target-container module. This component is subjected to the most severe conditions, in terms of the radiation effects, stress, and compatibility with mercury. A description of the target-container module and the overall materials R&D program is given in References 3 and 4. The H. TIAN, formerly Research Assistant, Department of Materials Science and Engineering, The University of Tennessee, Knoxville, TN 37996-2200, is Research Associate, Idaho National Laboratory, Idaho Falls, ID 83415-2218. P.K. LIAW, Professor and Iran Rachaff Chair of Excellence, D.E. FIELDEN, Staff Member, C.R. BROOKS, Professor, and M.D. BROTHERTON, Research Assistant, are with the Department of Materials Science and Engineering, The University of Tennessee, 434 Dougherty Hall, Knoxville, TN 37996-2200. Contact e-mail: [email protected] L. JIANG, Materials Scientist, is with the GE Global Research Center. B. YANG, Research Associate, H. WANG and J.P. STRIZAK, Research Staff Members, and L.K. MANSUR, Materials R&D Leader, are with the Oak Ridge National Laboratory, Oak Ridge, TN 37831. Manuscript submitted October 25, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
SNS will operate in a pulsed mode, with a proton-beam pulse frequency of 60 Hz. These pulsed fluxes also lead to pressure waves in the mercury created by beam heating, which, in turn, produce time-varying stresses that cause fatigue loading of the vessel at different frequencies and loading modes. The stress mode changes at different parts of the container. Two of the most common loading conditions are the tension-tension and tension-compression stress modes. Thus, it is important to study the fatigue behavior of type 316 LN SS under these stress modes. However, most of the mechanical data for 316 LN SS have been gathered in monotonic-loading conditions, and relatively less information for fatigueloading conditions has been obtained.[5,6] Some studies have been performed on 316 LN SS by the Oak Ridge National Laboratory, on the tensile behavior of irradiated specimens[7,8] and on 316 L with regard to liquid-metal corrosion and embrittlement, when the metal is in co
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