Synchrotron Based X-Ray Strain Mapping in Fatigued Materials Subjected to Overload

摘要

Fatigue crack growth involves localized fracture at the crack tip, and it intrinsically depends upon the local internal strain/stress fields and accumulated damage in the vicinity of the tip. The purpose of this report is to directly correlate variations in crack growth rate with variations in the relevant local strains around the crack tip. The so-called 'overload effect', namely the prominent crack growth rate retardation after a single overload cycle in an otherwise constant amplitude is studied. Our high spatial resolution measurements around fatigue crack are greatly facilitated by indexing our measurements to the fatigue crack itself. This crack based positioning is accomplished by measuring the beam intensity transmitted through the sample, with a transmission detector, so that a radiographic transmission profile can be constructed. Such transmission profiles enabled precise location of the crack and the crack tip in the x-ray beam.