Development of Fatigue and Crack Propagation Design and Analysis Methodology in a Corrosive Environment for Typical Mechanically-Fastened Joints. Volume 2. State-of-the-Art Assessment

摘要

Navy corrosion fatigue design requirements for metallic airframes and general design practices for satisfying these requirements are briefly reviewed. The phenomenon of and mechanisms responsible for corrosion fatigue crack initiation are reviewed. The mechanisms discussed include the stress-concentration pit mechanism, the film rupture mechanism, and the preferential dissolution mechanism. Two fracture mechanics models are described and discussed for quantitatively predicting the number of cycles to corrosion fatigue crack initiation: stress-initiation life model and strain-initiation life model. Methods are also discussed for using these initiation models for spectrum loading applications. Corrosion fatigue crack propagation mechanisms are reviewed and existing models are critiqued. Propagation models evaluated include a surface reaction controlled model, a transport controlled model, and a diffusion controlled model. These models recognize hydrogen embrittlement as the overwhelming cause of corrosion fatigue propagation enhancement. Models for load-environment interaction are described and discussed, including the generalized Wheeler model, the generalized Willenborg model, the generalized Closure model and the Vroman/Chang model.