Volume 1, Issue 9 (October 2004)
Development of a DCPD Calibration for Evaluation of Crack Growth in Corner-Notched, Open-Hole Specimens
A direct current potential drop (DCPD) calibration was developed for an open-hole specimen to characterize fatigue crack growth (FCG) behavior of cracks initiating from a small corner flaw and transitioning to a through-thickness crack. A single Mode I stress intensity (KI) solution was derived covering the entire range of crack growth. The purpose of using this specimen geometry was to: 1) capture short crack behavior for specific crack length intervals of damage tolerance criteria and 2) use the data to evaluate predictive FCG methodology. Driven by these objectives, a non-standard specimen was chosen that better simulated the geometry and stress state of the component of interest: an aircraft wing design detail. Thin panels of selected 7XXX and 2XXX aluminum alloys were prepared with a centrally located open-hole with a corner notch of 0.13 mm (∼0.005 in.) to serve as a crack initiation site. Testing was conducted in high-humidity air under constant and variable amplitude loading. Short crack 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. Evaluation of the predictive methods is beyond the scope of this paper and will be published separately.