A microstructural interpretation of the fracture strain and characteristic fracture distance

Fracture toughness is a function of both the spacing of the primary inclusions and the extent of growth of the voids nucleated at these inclusions. Only by includng the effect of void growth can the high toughness of the HP 9-4-20 be understood. The HP 9-4-20 and the base + Ni + Si steel have comparable values of X /SUB O/ , but the higher toughness of the HP 9-4-20 is due to a much larger value of (R /SUB V/ /R /SUB I/ )exclamationR /SUB o/ . Second, there should be a close relationship between the growth of the voids nucleated at the primary inclusions and the measure of ductility appropriate to the characteristic distance model of ductile fracture. Finally, it is suggested that the characteristic fracture distance will be determined by both the spacing of the primary inclusions and the extent of growth of the voids which they nucleate. It is emphasized that these comments apply only to alloys containing a unimodal dispersion of primary inclusions which are weakly bound to the matrix. Distributions of much smaller particles strongly bound to the matrix are admissible, but large inclusions strongly bound to the matrix are not