Effects of a Straightening Operation on Performance of Inconel 550 Buckets Page: 4 of 26
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NACA RM E55L06 3
The straightened buckets (group 1) were not inserted in the test
w wheel until 438 hours at rated speed had been accumulated on the engine.
This was done as a precautionary measure to protect another alloy being
run in the same engine test, because it was feared that the straightened
buckets might fail near the base of the airfoil. Such failures in past
investigations of this type have resulted in severe damage to the remain-
ing buckets in the engine. Normally, bucket failures occur in the mid-
dle third of the airfoil, and fractured fragments pass from the engine
without doing serious damage to the other buckets.
Engine Operation
The buckets selected for engine evaluation were operated in a J33-9
engine under cyclic conditions. Cycles were of 20-minute duration and
consisted of 15 minutes at rated speed of 11,500 rm and approximately
5 minutes at idle speed of 4000 rpm.
Engine operation was interrupted to obtain data on bucket elonga-
tion, to check buckets for cracks, to replace failed buckets, to over-
haul the engine when necessary, and to shut down at the end of each day.
The engine testing phase of the investigation was terminated after 878
hours (rated speed).
Stress and temperature distribution in turbine buckets during engine
operation. - Since the buckets used for this study were from the same
lots as those of reference 1, the centrifugal stresses and temperature
distribution for these buckets would be the same as those of reference
1 (see fig. 1).
Bucket temperatures were measured during engine operation with two
thermocoupled S-816 buckets. Temperatures were recorded by an electronic
potentiometer.
Bucket-elongation measurements. - Two buckets of each group were
scribed at 1/2-inch intervals, as shown in figure 2. Elongation meas-
urements were made at approximately 8-hour intervals for the first 25
hours of test time and at approximately 20-hour intervals for the re-
mainder of the test life. The elongation of each scribed segment was
measured with an optical extensometer having a sensitivity of 0.001 inch.
Accuracy of the elongation measurement is, however, influenced by the
degree of bucket distortion and warpage.
Macro- and microexamination of buckets. - Three buckets from one of
the groups (group 2) and six buckets from each of the other groups were
macroetched in an 80 percent HCL - 20 percent E202 solution to reveal
grain size and flow lines. These buckets were also used for macro- and
microstudies and stress-rupture tests.
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Gyorgak, C. A.; Johnston, J. R. & Weeton, J. W. Effects of a Straightening Operation on Performance of Inconel 550 Buckets, report, February 29, 1956; (https://digital.library.unt.edu/ark:/67531/metadc62056/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.