Effect of Size on the J Fracture Criterion

Abstract

Experimental evidence showing the size dependence of Ju in ferritic steels is presented. This behavior is described in terms of a relatively simple mechanistic model for cleavage fracture. It is shown that the mechanisms of cleavage fracture and ductile slow crack growth are always in competition and this leads to the behavior frequently encountered in fracture tests where initially ductile crack extension leads to fast brittle failure. The size eifect is also discussed in terms of a shift in the ductile brittle transition temperature. The implications on failure assessment procedures are mentioned.