Study of the Influence of Metallurgical Factors on Fatigue and Fracture of Aerospace Structural Materials
Abstract
Direct SEM measurement of closure local to crack tips in several structural alloys was performed. Growth rates for both large and small cracks in an aluminum alloy, a nickel-base superalloy, and an intermetallic alloy were correlated by formulating correctly the crack driving force. It was determined that apparent differences in crack growth rates under varying circumstances, including variable amplitude loading, were caused not by differences in the intrinsic crack advance mechanism, but rather by inaccuracies in determining the proper transfer function between the conventional cyclic stress intensity, and the true local crack driving force. The relationship between microstructure and fracture toughness was investigated for state-of-the-art Al-Fe-X alloys. Relevant fracture mechanisms and origins of fracture toughness were identified, and analyzed in terms of microstructural factors (dispersoids and oxide fragments). The origin of the brittle-to-ductile transition in Al-Fe-X was identified, and shown to be controlled by the tearing modulus. Concepts for increasing toughness were established. Aircraft.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1989
- Accession Number
- ADA206605
Entities
People
- David L. Davidson
- Gerald R. Leverant
- James Lankford
- Kwai S. Chan