Plane strain deformation experiments were performed on elliptical inclusion
s of cohesive sand embedded within a slab of pitch, with the aim of investi
gating the mode of fracturing of brittle inclusions within a ductile matrix
. Under pure and simple shear. the inclusions failed in three different mod
es: tensile fracturing (Mode 1), shear fracturing (Mode 2a) and extensional
shear fracturing (Mode 2b). Jeffrey's (1922) theory of the Row of a viscou
s medium around an ellipsoidal body was applied to the experimental results
to determine the principal tensile and compressive stresses within an incl
usion, and analyze the failure modes using Griffith's Criterion. The analys
is reveals that the aspect ratio (R) and the orientation (theta) of the inc
lusion control the principal tensile and compressive stresses within it, an
d in turn govern the mode of brittle deformation. At a particular inclusion
orientation. the tensile stress increases, whereas the compressive stress
decreases monotonically with increasing aspect ratio of the inclusion. The
principal stresses also vary with inclusion orientation for a given aspect
ratio, but not monotonically. The analysis delimits the Fields of each mode
of brittle deformation of inclusions in R- theta space under pure shear an
d simple shear. (C) 2001 Elsevier Science Ltd. All rights reserved.