Corrosion and Corrosion Fatigue of Airframe Materials.

In support of the National Aircraft Research Program of the Federal Aviation Administration FAA Lehigh University undertook a multidisciplinary program of research to study corrosion and corrosion fatigue of airframe materials. The program is complemented by a program sponsored by the Air Force Office of Scientific Research AFOSR. The objectives of these programs are 1 the development of basic understanding of the processes of localized corrosion and corrosion fatigue crack nucleation and growth in high-strength aluminum alloys used in airframe construction 2 the formulation of kinetic models for these elemental processes and 3 the integration of these models into probabilistic models that can provide guidance in formulating methodologies for service-life prediction. This report summarizes research performed under the FAA sponsored Phase I program for the period from 15 June 1992 to 14 June 1995. Experimental efforts during this period were focused upon 1 characterizations of the chemical microstructural and statistical aspects of pitting corrosion, and upon the kinetics of pitting of 2024-T3 aluminum alloy in aqueous environments 2 establishment of the criteria for the transition from pitting to corrosion fatigue crack growth i.e. crack nucleation and 3 studies of corrosion fatigue crack growth particularly in its early stage, or the so-called chemically short regime. The modeling effort, which cuts across the FAA and AFOSR programs, included the development and demonstration of a mechanistically based probability approach for service-life prediction and the formulation of a probability model for particle-induced corrosion pit growth that pertains to multiple-site-damage MSD analysis.