NUCLEATION AND BLUNTING OF NANOCRACKS IN BRASS

In situ tensile test of brass foil specimens in TEM shows that many di slocations were emitted from a loaded crack tip and a dislocation free zone (DFZ) was formed under condition of constant displacement. The D FZ is an elastic zone, where the stress may equal to the cohesive stre ngth sigma(th) when the applied stress is high enough. As a result, na nocracks would initiate discontinuously in the DFZ or, sometimes, at a blunted-crack tip. As soon as the nanocrack nucleated, it quickly blu nts into a void, which results in ductile fracture.