Fatigue Crack Growth in Damage Tolerant Al-Li Sheet Alloys.

摘要

Modern Al-Li alloy development is motivated by prospective weight savings owing to decreased density and increased stiffness as compared with conventional alloys. Improvements in density and stiffness are joint consequences of lithium additions. Thus alloy development may be considered successful -in engineering terms- if other properties are simply maintained. This is the development strategy for damage tolerant Al-Li alloys. The present work compares the fatigue crack growth properties of two candidate damage tolerant Al-Li sheet alloys, 2091 and 8090, with those of the conventional and widely used 2024 alloy. There were three load histories: constant amplitude, gust spectrum, and constant amplitude with occasional peak loads. The results are interpreted with the aid of fractographic observations and measurements of fracture surface roughness. The practical significance of the results is assessed, and recommendations are made for further evaluations.