Crack Initiation and Growth Behavior at Corrosion Pit in 7075-T6 High Strength Aluminum Alloy
Abstract
Research on fatigue crack formation from two types corrosion pits tangent to a circular hole in a 7075-T6 aluminum alloy subjected to uni-axial loads (R = 0.5, lambda = 0) in both an air and saltwater environment provides a method for exploring crack initiation and initial growth rates. This work focuses on a fracture mechanics approach to explore the transition from corrosion pit to crack growth. Specimens with a cylinder shaped through-pit tangent to a circular hole have a closed form solution to predict this delta K that closely resembles the finite element solutions. Specimens with a semi-circular corner-pit tangent to hole lack a closed form solution and finite element modeling was used to determine delta K of these specimens. Optical and electron microscopy provided an accurate way to measure and observe the crack growth rate (da/dN) and the cycles until initiation of the fatigue cracks. This research shows that corner-pit specimens initially have a slower crack growth rate than through-pit specimens due to the propagation of a quarter-circular crack front through the thickness of the sample. After initial crack growth, both corner-pit and through-pit samples have the same growth rate as their machine notched counterparts exposed air and saltwater environments.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2013
- Accession Number
- ADA581422
Entities
People
- Eric M. Hunt
Organizations
- Air Force Institute of Technology