Effect of overheating on creep-rupture properties of S-816 alloy at 1,500 degrees F Page: 4 of 76
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NACA TN l081
(1) Change of creep-rupture life due to the exposure to a higher
temperature changing the internal structure of the metal. This effect
is designated "temperature damage" in subsequent discussions.
(2) Acceleration of creep when the temperature is increased in the
presence of stress, subsequently referred to as "stress damage."
In addition, the cyclic removal and reapplication of the stress
during the overheat experiments in the absence of stress could alter
the creep-rupture characteristics. The influence of overheats could
also be expected to vary depending on the stress level and rupture time
at the nominal test temperature. In consideration of these factors,
the following general experimental program was established.
Determination of Temperature Damage From Overheating
in Absence of Stress
The following data were obtained in the determination of temperature
. _Fdamage from overheating in the absence of stress:
(1) The basic measurement was the effect on rupture time of continu-
ous cyclic overheats to 1,6500, 1,8000, 1,9000, and 2,0000 F until rupture
occurred. For tests under a 16,200-psi stress at 1,5000 F (rupture in
1,210 hours) the load was removed and an overheat applied twice daily.
For tests under a 22,000-psi stress at 1,5000 F (rupture in 94 hours)
the overheats were applied every 5 hours.
(2) The accumulative damage of overheats was established by stopping
the overheats after various amounts of the total rupture life had been
used up. The tests were then allowed to proceed to rupture at a constant
load at 1,5000 F. This procedure enabled the development of curves of
percent of the nominal life at 1,5000 F against the amount of overheating.
(3) The relation of the occurrence of overheating to the degree to
which creep had proceeded at 1,5000 F was checked by delaying overheats
until the second stage of creep. This provides information as to whether
there is a difference in the damage from overheats depending on the degree
of prior service.
As part of this procedure, specimens were overheated before starting
the rupture tests at 1,5000 F. This type of test would primarily indi-
cate whether such experiments provide reliable data regarding the effects
of overheats during service.
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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/m1/4/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.