AN ANALYSIS OF DUCTILE FRACTURE INITIATION TOUGHNESS IN IRON, ITS BINARY-ALLOYS AND NICKEL

The ductile crack initiation toughness (J(IC)) data, obtained for a nu mber of single phase, essentially particle-free materials, have been a nalysed in light of the existing models for J(IC) developed for engine ering alloys having a substantial volume fraction of second phase part icles. The mechanism of void nucleation ahead of the blunted crack and also the characteristic distance (l(c)) of the void from the crack ti p in single phase materials have been determined through a careful exa mination of the interrupted fracture toughness test specimens. The pap er presents an approach to the calculation of J(IC) in terms of the cr itical strain criterion model originally developed by Rice and Johnson and Ritchie and Thompson. This approach not only incorporates the exp erimentally measured l(c) values but also the plastic flow related ene rgy dissipation in the Hutchinson-Rice-Rosengren (HRR) zone beyond the process zone. It is shown that the suggested approach is capable of e stimating J(IC) for a number of single phase materials with a wide ran ge of measured J(IC) values.