Direct, Real Time Observation and Mechanism of Fatigue Crack Growth

Relation between Growth Rate and Crack Tip Opening Displacement

Abstract

Fatigue crack growth tests were performed on grain-oriented 3% silicon iron in a high-resolution, field emission type scanning electron microscope, using a specially designed servo-hydraulic fatigue loading system, and direct, real time observations of a growing fatigue crack were made.
Good correlation was found between crack growth rate, da/dn, and crack tip opening displacement, CTOD, under constant amplitude load testing. The ratio of growth increment to CTOD, however, was reduced with decrease of crack growth rate. Fatigue crack growth behavior and relation between growth rate and CTOD under Hi-Lo two step loading tests were also discussed.