A test specimen was developed to characterize growth behavior of fatigue cracks initiating from a corner flaw and growing to a through-thickness crack. Panels of various 7XXX and 2XXX aluminum alloys wee prepared with a centrically located open-hole with a corner notch on the order of 0.13-mm (0.005-in) to serve as a crack initiation site. A direct current potential drop (DCPD) calibration and stress intensity factor solution were formulated to describe partial-thickness crack growth from the initial starter notch through transition to a full-thickness crack. Testing was conducted in high-humidity air under constant and variable amplitude loading using servo-hydraulic equipment under computer control. Results agreed well with existing, closure-corrected long-crack data. Duplicate tests of the 7XXX alloys confirmed repeatability. The 2XXX alloys exhibited greater variability than the 7XXX alloys in the short crack regime. This was attributed to the larger grain size and more tortuous crack path observed in the 2XXX alloys.
With K. George, J. K. Donald, and R. J. Bucci, "Development of a Corner-Notched, Open-Hole Specimen for Material Evaluation," in Fatigue Testing and Analysis under Variable Amplitude Loading Conditions, STP 1439, P. C. McKeighan and N. Ranganathan, Eds. American Society for Testing and Materials, 2002.