Bs. Henry et Ar. Luxmoore, THE STRESS TRIAXIALITY CONSTRAINT AND THE Q-VALUE AS A DUCTILE FRACTURE PARAMETER, Engineering fracture mechanics, 57(4), 1997, pp. 375-390
Ductile fracture of metals occurs as a result of nucleation, growth an
d coalescence of microscopic voids that initiate at inclusions and sec
ond phase particles. The main parameters that influence void nucleatio
n and growth, and hence ductile fracture, are the triaxiality factor a
nd the plastic strain. The triaxiality factor is widely used as a cons
traint parameter. Recent advances highlight the loss of J-dominance in
low constraint geometries and the importance of using two-parameter t
heories, namely J-T and J-Q to characterise near crack front states of
yielded crack geometries. In this paper we use three-dimensional fini
te element models of low constraint geometries to study the variation
of the triaxiality factor, plastic strain and e-value with the deforma
tion level. Comparisons between the triaxiality factor, the plastic st
rain and the e-value are made at different distances ahead of the crac
k front. Our numerical results show that, for a given material, there
exists a unique linear relationship between the triaxiality factor and
the e-value that is independent of specimen geometry, dimensions, cra
ck depth and deformation level. This unique relationship shows that th
e e-value dan be used as a ductile fracture parameter as it parameteri
ses both the stress triaxiality and the plastic strain. It can be conc
luded that the e-value and the stress triaxiality factor are equivalen
t constraint parameters. (C) 1997 Elsevier Science Ltd.