MICROMECHANISM OF DUCTILE FRACTURE INITIATION- VOID NUCLEATION AND GROWTH UDC 539.421:621.039.542.3

Abstract. Micromechanism of ductile fracture of most metals and alloys includes void nucleation, growth and coalescence. The voids nucleate at the second phase particles and non-metallic inclusions. Application of so-called global criteria of fracture mechanics such as COD and J-integral in characterization of ductile fracture onset does not provide satisfactory results for all cases of external loading. The problems arising in solving the phenomenon of severe plastic strain at crack tips and application of the results obtained to describe behaviour of various structures of different geometry are not insignificant. In present paper micromechanical model based on a particular criterion of flow in a porous solid has been applied. The model was initially established by Gurson, and later on modified by Tvergaard and Needleman. Unlike traditional flow criteria (for instance, with metals widely applied Von Mises criterion), established flow criterion introduces volume fraction (f) variable. Through application of this model, by combining experimental and numerical procedures, an effort is made to predict ductile fracture of metals. In present paper fracture initiation of smooth specimen has been analyzed; described model was incorporated into finite element (FE) program, so tha