Fracture and Fatigue-Crack Propagation Characteristics of 7075-T7351 Aluminum Alloy Sheet and Plate

摘要

The program was directed to provide information relative to damage tolerance of panels of 7075-T7351 sheet and plate. This implied the generation and analysis of information on flat panels containing centrally located flaws and testing, either under monotonically increasing load or under cyclic loads. The information obtained provided insight into the two major aspects of damage tolerance - residual strength and fatigue-crack propagation - from tests on panels ranging in thickness from 1/16 inch to 1 inch and in width from 8 inches to 36 inches. The program has shown that there are at least two bench marks in crack growth behavior from the monotonically increasing load test: (1) onset of slow growth at which a flaw initially present begins to grow slowly with increasing load, and (2) critical instability at which unstable and rapid crack growth occurs that results in failure. From the data obtained a generalized residual strength analysis was developed which identifies a fracture toughness property for thin and transition thickness materials as well as presents design data and fracture or residual strength predictions for structural applications. The program has also resulted in the identification of an empirical expression that appears to be quite useful in predicting fatigue-crack propagation and the remaining lifetime of a panel containing a fatigue crack. (Author)