Abstract :
Dynamic ductile fracture is a three stages
process controlled by nucleation, growth and
finally coalescence of voids. In the present work,
a theoretical model, dedicated to nucleation and
growth of voids during dynamic pressure loading, is
developed. Initially, the material is free of voids but
has potential sites for nucleation. A void nucleates
from an existing site when the cavitation pressure
pc is reached. A Weibull probability law is used
to describe the distribution of the cavitation pressure
among potential nucleation sites. During the
initial growth, the effect of material properties is
essentially appearing through the magnitude of pc.
In the later stages, the matrix softening due to the
increase of porosity has to be taken into account.
In a first step, the response of a sphere made of
dense matrix but containing a unique potential
site, is investigated. When the applied loading is
a pressure ramp, a closed form solution is derived
for the evolution of the void that has nucleated
from the existing site. The solution appears to bevalid up to a porosity of 0.5. In a second part, the
dynamic ductile fracture of a high-purity grade tantalum
is simulated using the proposed model. Spall
stresses for this tantalum are calculated and are
in close agreement with experimental levels measured
by Roy (2003, Ph.D. Thesis, Ecole Nationale
Supérieure deMécanique et d’Aéronautique,
Université de Poitiers, France). Finally, a parametric
study is performed to capture the influence of
different parameters (mass density of the material,
mean spacing between neighboring sites, distribution
of nucleation sites. . .) on the evolution of
damage.
