Improvement of Fracture Toughness and Low-Cycle Fatigue Life for INCONEL718 Welded Joint in the LE-7 Rocket Engine Main Injector

Welded joint structural failure has been observed in the LE-7 engine main injector, which is subjected to high thermal stress during an engine start and stop sequence. Failure analysis showed that these failures were caused by extremely-low-cycle fatigue due to a low number of hot-fire tests in a ve...

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Bibliographic Details
Published inTransactions of the Japan Society of Mechanical Engineers Series A Vol. 61; no. 588; pp. 1707 - 1712
Main Authors Hasegawa, Keiichi, Ando, Kiyoshi, Kitade, Shouji, Sakamoto, Mitsumasa, Fukushima, Yukio, Okita, Koichi
Format Journal Article
LanguageJapanese
Published The Japan Society of Mechanical Engineers 1995
Subjects
Fracture Toughness
INCONEL718
LE-7
Low-Cycle Fatigue
Rocket Engine
Solution Heat Treatment
Thermal Shock
Thermal Stress
Welded Joint
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Summary:Welded joint structural failure has been observed in the LE-7 engine main injector, which is subjected to high thermal stress during an engine start and stop sequence. Failure analysis showed that these failures were caused by extremely-low-cycle fatigue due to a low number of hot-fire tests in a very high-strain condition. It was revealed that the welded joint has a considerably short low-cycle fatigue life and low fracture toughness, contrary to expectation. Based on several kinds of material tests, countermeasures such as design change of the welded structure, modification of the welding process, strengthening during non-destructive inspection and application of solution heat treatment were taken to improve welded joint strength characteristics. Using the modified main injector, a complete qualification test of LE-7 engine was performed without occurrence of failure and the first H-II rocket was launched successfully.
ISSN:0387-5008
1884-8338
DOI:10.1299/kikaia.61.1707