Method for Relating Plastic Flow Properties to Fatigue Crack Propagation Including Effects of Stress Ratio

摘要

Accurate predictive models for fatigue crack propagation, including effects of mean stress, could expedite material characterization tasks of the Navy. To this end, the accuracy of the tensile ligament instability model of fracturing has been improved by considering that the crack-growth-induced strain hardening, which stabilizes creep-induced stress-relaxation,is that of plastic flow only, rather than that of elastic plus plastic strain. R-effect data on Ti-6Al-4V from two literature sources is examined. The growth in vacuum is simply predicted, while that in air must be corrected for its faster growth rate and lower threshold of zero growth. A simple graphical method for matching predicted to actual growth is described. Procedures include SI as well as English units of measurement.