Effect of overheating on creep-rupture properties of S-816 alloy at 1,500 degrees F Page: 3 of 76
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NACA TN 4081
An investigation was carried out to evaluate the effects of brief
overheats to temperatures of 1,6500, 1,8000, 1,9000, and 2,0000 F on the
creep-rupture properties of S-816 alloy at 1,5000 F. The objective of
the investigation was to obtain basic information on the changes in
creep-rupture properties of the alloy due to overheating which can occur
during jet-engine operation.
The effects of overheating were evaluated in terms of the changes
in creep-rupture characteristics at 1,5000 F under stresses within the
range of rupture strengths of the S-816 alloy for 100 to 1,000 hours.
The possible damage from overheating was considered to include internal
metal structure changes induced by exposure to the higher temperatures
and loss in life by creep if stress was present during the overheats.
Temperature damage was evaluated by starting tests at 1,5000 F and then
periodically overheating with the stress removed during the overheat
periods. Stress damage during overheats was evaluated by leaving stress
on the specimens during the overheats.
Overheat periods were predominately 2 minutes in duration and were
applied cyclically at approximately 5- or 12-hour intervals. These
schedules were adopted to provide the most useful general results after
consideration by the Subcommittee on Power-Plant Materials of the
National Advisory Committee for Aeronautics of the variable conditions
under which overheating can occur in jet-engine service. It should be
clearly recognized that the intent was to develop general principles and
not to evaluate the specific conditions of overheating which can occur
in a specific jet engine. The investigation was also limited to the
effects on creep-rupture properties. The overheat conditions did not
include the effects of differential restrained expansion (thermal shock)
or the possible effects on such other properties as fatigue strength
and corrosion resistance.
This investigation was carried out by the Engineering Research
Institute of the University of Michigan under the sponsorship and with
the financial assistance of the NACA. It was part of a general research
investigation studying metallurgical factors involved in the use of heat-
resistant alloys in aircraft propulsion systems.
Overheating can be expected to have two main effects on creep-
rupture life at some lower nominal temperature:
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Rowe, John P. & Freeman, J. W. Effect of overheating on creep-rupture properties of S-816 alloy at 1,500 degrees F, report, December 1957; (https://digital.library.unt.edu/ark:/67531/metadc57081/m1/3/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.