FRACTURE MODES ENCOUNTERED FOLLOWING THE APPLICATION OF A MAJOR TENSILE OVERLOAD CYCLE

Monotonic modes of failure, induced at the fatigue crack tip by application of a major tensile overload cycle, have been studied in a low-carbon structural steel. Tests were performed on fatigue cracks grown at a load ratio of 0.6 and a constant baseline stress intensity range corresponding to fatigue crack growth rates in the Paris regime. Both void growth and quasi-cleavage fracture were observed at the overload location. The quasi-cleavage fracture was associated with increased post-overload fatigue crack growth rates, prior to the occurrence of a transient retardation of the growth rate. A residual compressive stress field, generated by the overload cycle, ahead of the blunted crack tip was considered to be the primary mechanism responsible for the retardation phenomenon.