Stress Relaxation Testing of Service Exposed IN738 for Creep Strength Evaluation PUBLIC ACCESS

[+] Author Affiliations
David A. Woodford

Materials Performance analysis, Inc., Santa Barbara, CA

Paper No. 99-GT-285, pp. V004T01A003; 8 pages
  • ASME 1999 International Gas Turbine and Aeroengine Congress and Exhibition
  • Volume 4: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; IGTI Scholar Award; General
  • Indianapolis, Indiana, USA, June 7–10, 1999
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7861-3
  • Copyright © 1999 by ASME


Standard size and miniature specimens of IN738 were taken from a service exposed turbine blade and vane for comparative stress relaxation testing at 800C, 850C and 900C. Base data taken from root section material were used to construct stress vs. creep rate parametric curves which could be used directly in design. Up to five decades in creep rates were obtained at each temperature from tests lasting less than one day. The data were also presented in the form of stress vs. predicted times to 0.5% creep which compared well with available long time creep data. Differences were noted in specimens taken from different locations in the airfoil regions which probably resulted from differences in grain size or orientation. Based on these measurements it was concluded that there was no significant effect of section size on creep strength as defined by this test, and that the alloy was quite insensitive to prior deformation and thermal exposures. A life management procedure, using a combination or creep strength evaluation based on the stress relaxation test and a separate fracture evaluation measurement, is outlined in which end of useful life is defined in terms of minimum acceptable performance levels.

Copyright © 1999 by ASME
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