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Alloys investigated were Nimonic 90, IN 100, coated IN 100, B 1900, coated B 1900, MAR M200, and MAR M200DS (directionally solidified). Maximum temperatures ranged from 770 to 1120 C (1420 to 2050 F). Specimen geometries included tapered disks, double-edged wedges, and cambered airfoils. The disks and wedges were heated and cooled in fluidized beds. The airfoil specimens were heated by a Mach 1 natural gas burner and rapid-air cooled, with and without spanwise loading. Life calculations included two distinct failure modes: conventional low-cycle fatigue and cyclic creep. Required material properties were limited to conventional thermal, tensile, and creep-rupture data. The complete life calculation system included the calculation of transient temperature distributions, thermal strains, stresses, creep damage, fatigue damage, and finally cycles to first crack. Calculated lives were within a factor of two for 76 of the 86 data points analyzed. Cyclic creep accounted for 80 per cent of all the calculated damage.
nickel alloys, thermal fatigue, creep properties, fatigue (materials), stress cycle, grain size, crack initiation, damage, stress analysis
Consultant, Fatigue Branch, Lewis Research Center, National Aeronautics and Space Administration, Cleveland, Ohio