Abstract :
Slant fracture iswidely observed during
crack growth in thin sheet specimens made of ductile
materials, providing a good case for investigating
three-dimensional criteria for mixed-mode
ductile fracture. To gain an understanding of slant
fracture events and to provide insight for establishing
a slant fracture criterion, stable tearing fracture
experiments on combined tension-torsion (nominal
mixed-mode I/III) specimens and nominal
Mode I Arcan specimens made of Al 2024-T3 are
analyzed using the finite element method under
three-dimensional conditions. Two types of finite
element models are considered for the study of
slant fracture: (a) combined tension-torsion specimens
containing stationary, flat and slant cracks
subject to loads corresponding to the onset of crack
growth, and (b) stable tearing crack growth with
slanting in a nominal Mode I Arcan specimen.
Analysis results reveal that there exists a strong
correlation between certain features of the crackfront
effective plastic strain field and the orientation
of the slant fracture surface. In particular, itis observed that (a) at the onset of crack growth
in the combined tension-torsion experiments, the
angular position of the maximum effective plastic
strain around the crack front serves as a good
indicator for the slant fracture surface orientation
during subsequent crack growth; and (b) during
stable tearing crack growth in the Mode I Arcan
specimen, which experiences a flat-to-slant fracture
surface transition, the crack growth path on
each section plane through the thickness of the
specimen coincides with the angular position of
the maximum effective plastic strain around the
crack front.
