The local cleavage fracture stress σF measured atthe cleavage initiation sites of a granular bainitic weld metal isonly an apparent fracture parameter dependent on stresstriaxialities at the local sites in the propagation controlledcleavage regime. This dependence can be explained by the stresstriaxiality modified Smith equation in which the intrinsiccleavage fracture stressσF 0 is introduced, considered to be aninvariant characterizing a material's fracture property. In thenucleation controlled cleavage regimeσF is temperaturedependent and coincident with the local yield stresses defined byVon Mises criterion at the local sites.It is suggested that the modified Smith model would provide aunified physical basis for the intrinsic correlation among variousmacroscopic fracture properties as well as their temperaturetransition behaviors from the temperature dependence ofmaterials' yield strength.
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