Modeling creep and fatigue of copper alloys
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I. INTRODUCTION
COPPER alloys, with their combination of high thermal conductivity and relatively high mechanical strength and toughness over a wide range of temperatures, are likely the best materials for complex structural applications subjected to conditions of extreme heat flux under load. Such applications range from molds for the continuous casting of steel[1–4] to the first wall of a fusion reactor.[5–8] Continuous-casting molds must withstand contact with molten steel and remove sufficient heat to continuously solidify a solid shell. To produce high-quality steel slabs, billets, and strip, a copper mold must maintain tight dimensional tolerances and consistent surface temperatures while being subjected to constant thermal cycling (due to both short and long liquid level changes). To be economical, it must survive many months with minimum wear while over 50,000 tons of steel is pulled through it. Most important of all, it must be 100 pct safe from complete fracture, because contact between the molten steel and cooling water (separated by only a thin layer of copper) could be catastrophic.[2] New alloys are difficult to introduce, owing to the difficulty of safely demonstrating their ability to satisfy these requirements. The first wall of the proposed fusion reactor, ITER (international thermonuclear experimental reactor), must be designed to face both thermal and nuclear radiation from several million 8C plasma. This thin wall must maintain dimensional stability and withstand stresses induced by mechanical loads and temperature gradients as well as the irradiation creep and swelling induced by the high neutron fluence.[6,7,8] Achieving and proving reliable performance of the first-wall material is a key technical challenge that may determine the feasibility of commercial fusion reactors. Despite the widespread use of stainless steel in current G. LI, formerly Graduate Student, Department of Nuclear Engineering, University of Illinois, is Lead Engineer in Heat Transfer and Fluid Systems Design, AEPD, General Electric Aircraft Engines, Cincinnati, OH 452156301. B.G. THOMAS, Professor, Department of Mechanical and Industrial Engineering, and J.F. STUBBINS, Professor and Head, Department of Nuclear, Plasma and Radiological Engineering, are with the University of Illinois at Urbana-Champaign, Urbana, IL 61801. Manuscript submitted July 20, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
nuclear reactors, copper alloys are the leading candidate materials for the ITER first wall. The accurate prediction of the mechanical behavior and lifetime of the entire structure is crucial to applications such as these. To do this requires accurate models that include a robust characterization of material properties such as the thermal conductivity, thermal-expansion coefficient, and mechanical constitutive relations. The latter includes elastic, plastic, and creep behavior and fracture toughness, crack growth, and failure prediction under a variety of loading conditions, such as fatigue cycling. Furthermore, these constants
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