Fatigue and Fracture Characterization of Aircraft Aluminum Alloys Damaged by Prior Corrosion
Abstract
At the time of the initiation of this project, there was no comprehensive data describing corrosion's effect on the fatigue and fracture behavior of aluminum alloys typically found in aging aircraft. One of the primary objectives of this project was to perform experimental and analytic characterizations of these materials response for three aluminum alloys (2024-T3, 7075-T6 and 7178-T6, all widely used in order aircraft) in the presence of prior corrosion. Because the typical aircraft's operation cycle leads to the supposition that corrosion and fatigue are series events (as opposed to simultaneous corrosion and fatigue), we made experimental test specimens that had artificially-grown corrosion damage in them. The aim was to develop the necessary material response data to be used in structural integrity inspection interval determinations. Specifically, fatigue crack growth rates and fracture toughness data were developed. For each alloy, the experimental variables were material condition (ranging from no corrosion through several degrees of damage), stress ratio and relative humidity in the air environment. Here, we quantified corrosion damage as the percent of material lost, based on the nominal specimen thickness A multiple replication factorial experimental design provided the data and analysis of variance techniques were used to address the hypotheses that the experimental variables affect the crack growth rates and that any observed differences can be accounted for by considering only the thickness reduction caused by corrosion. For each alloy, crack growth rate relationships (e.g., da/dN versus delta K) were developed that account for corrosion damage. The fracture characterization focused on the plane stress fracture toughness values (K(sub c)) for varying levels of corrosion damage and varying specimen.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 19, 2002
- Accession Number
- ADA400498
Entities
People
- J. D. Baldwin
Organizations
- University of Oklahoma