1991 Volume 40 Issue 457 Pages 1310-1316
A crystallographic study has been performed on the growth behaviour of microstructurally small fatigue cracks using coarse grained materials of 3%Si iron. The orientation of grains around cracks was determined by analyzing etch pits developed on the specimen surface, and the correlations between the crack path or crack growth rate and the crystallographic parameters such as slip plane and slip direction were examined. Macroscopic growth direction of transgranular cracks tends to be consistent with the primary or secondary slip directions, or the resultant direction of both. Furthermore, the angle between the crack growth direction and the intersection of primary slip plane and specimen surface in adjacent grain exerts a significant influence on the growth behaviour. As the angle is larger than approximately 40°, cracks can not grow, or can grow with a marked deflection, into the adjacent grain. With increasing the angle, cracks show deep decrease in crack growth rate and/or temporary arrest at the grain boundary.
