Dislocation Transport of Oxygen During Fatigue Crack Growth.

摘要

Studies of particular interest to the aerospace industry, crack propagation under cyclic loading and environmental effects on the fatique crack growth rate are reported. An increase in growth rate in an oxygen environment as compared to growth rate in vacuum is indicated for Monel 404 and commercially pure titanium. Little increase in growth rate is observed for aluminum 7075-T651 and 2219-T87 alloys. Enhanced concentration of oxygen in the metal matrix due to propagation of a fatigue crack in an oxygen environment compared to a vacuum environment is indicated for Monel 404, commercially pure titanium, aluminum 7075-T651 and aluminum 2219-T87. This is consistent with a dislocation transport mechanism. Sample roughness appeared to contribute little error to the measurements. A rough estimate of dislocation transport depths of 125 to 600 A is made based on expected oxide thickness. The fracture surfaces from oxygen and vacuum environments appear the same for each material except Monel 404.