Mc. Burstow et Ic. Howard, PREDICTING THE EFFECTS OF CRACK-TIP CONSTRAINT ON MATERIAL RESISTANCECURVES USING DUCTILE DAMAGE THEORY, Fatigue & fracture of engineering materials & structures, 19(4), 1996, pp. 461-474
In recent years much interest has been focused on the geometry depende
nce of the resistance to stable ductile crack growth of engineering ma
terials, and in particular, in explaining this in terms of ''constrain
t'' effects. This paper describes the results of work using the Rousse
lier ductile damage model in finite element studies to simulate the gr
owth and coalescence of voids, and hence the mechanics of ductile crac
k growth, to predict the effect of constraint on resistance to fractur
e. Using the modified boundary layer solution, where constraint is con
trolled by the application of remote displacements, it was possible to
simulate resistance curves for different constraint conditions. This
has produced a ''net'' of resistance curves, within which the curve fo
r any specimen geometry can be found from a knowledge of the crack tip
constraint for that specimen. This has been tested by comparing the r
esults with those obtained from two specimens for which the constraint
conditions are known. Good agreement has been achieved. The results s
how that, although constraint has very little effect on conditions at
the crack tip at initiation of crack growth, beyond that constraint pl
ays an important part in defining the resistance curve. For low constr
aint geometries there is a very large loss in crack tip constraint whi
ch results in a large increase in the slope of the resistance curve. O
n the other hand, high constraint geometries exhibit very little depen
dence on crack tip constraint.