Fatigue crack growth tests were performed on randomly 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 growing fatigue crack were made.
In the regime with relatively low growth rates, fatigue crack growth behavior was strongly affected by grain orientation, and the growth direction and rate were found to differ depending on grains. However, the effect of grain orientation seems to disappear in the high growth rate regime. It was also found that the grain boundary had an obstructive effect on the transgranular crack growth rate and that the growth rate decreased when the crack tip approached to the grain boundary.
