Growth behavior of small surface cracks in coarse and ultrafine grained copper

Abstract

Since fatigue life of a plain specimen of ductile metals is controlled mainly by the propagation life of a small surface crack, to clarify the growth behavior of a small crack is crucial to the safe design of smooth members. However, little has been reported on the growth behavior of small surface cracks in ultrafine grained (UFG) metals. In the present study, stress-controlled fatigue tests for coarse grained (CG) and UFG copper were conducted. The surface damage evolution during cyclic stressing was observed by optical microscopy, and the growth behavior of a small surface crack was monitored by a plastic replication technique. The physical background of fatigue damage for CG and UFG copper was discussed from the viewpoints of the initiation and growth behavior of small surface cracks.