THERMAL-STRESS FATIGUE CRACKING OF TURBINE BUCKETS OPERATED AT 1700° F IN A TURBOJET ENGINE WITHnLONG PERIODS OF OPERATION BETWEEN STARTS

摘要

Thermal-stress fatigue cracking occurred in some buckets of each alloy group early in the test and in 48 to 100 percent of the buckets of each alloy group at the conclusion of the test (after 33 starts and 357 hr at rated speed). Although thermal-fatigue cracking occurred early, only two buckets fractured (broke into two or more pieces) during the test. Increased operating time between starts permitted substantial increases in accumulated rated-speed operating time for all alloys before bucket cracking occurred. Compared with the previous investigation (TN D-125) increased operating time between starts decreased the number of starts to cause cracking of buckets for alloys B & B and forged Udimet 500, but not for alloys Sel-1 and Inconel 713. Increased operating time between starts also increased the number of buckets cracked for a given number of starts for alloys Sel-1, B & B, and forged Udimet 500. The mode by which bucket cracks progressed to fracture was the same as described in TN D-125. The fractures occurred by mechanical-fatigue progression of thermal-stress fatigue cracks.