Combined Effects Testing for Aluminum Alloy Environment Assisted Cracking (C2026-00373)

Fritz Friedersdorf, Dan Christy, Lauren Askew, Carly Cocke

Aircraft structures and components are subjected to dynamic environmental and mechanical conditions during both ground and flight operations. Aerospace structures are fabricated from mixed materials that also include protective surface finishes. Atmospheric corrosion, especially at fasteners, may initiate stress corrosion cracking (SCC) and corrosion fatigue. Relevant laboratory and outdoor atmospheric testing of these material systems that includes combined effects of corrosion and mechanical loads is challenging. Recent research has focused on test system development and evaluation. The test system has been used to evaluate coatings and quantifying the influence of galvanic crevice corrosion processes on the development and propagation of environment assisted cracks. Drying and relative humidity thresholds are significant for SCC initiation and propagation for susceptible alloys. Two regimes of cracking may be observed; SCC at low stress intensity ranges and corrosion fatigue dominated propagation at higher stress intensity ranges. The operative mechanisms and stress dependent behavior are depend on environmental conditions, alloy SCC susceptibility, crack orientation, and loading frequency among other factors. It is expected that this test system and methods will be useful for corrosion risk reduction and improving our understanding of the environment, loads, and material interactions that are significant to aircraft structural integrity.