Abstract :
Crack deflection in single-crystal brittle occurs
when a crack, propagating on one cleavage plane,
‘chooses’, from energy considerations, to continue
propagating on another cleavage plane. This phenomenon
was identified during dynamic crack propagation
experiments of thin, rectangular [0 0 1] single-crystal
(SC) silicon specimens subjected to three-point bending
(3PB). Specimens with long pre-cracks (hence propagating
at a ‘low’ energy and velocity) cleave along
the vertical (1 1 0) plane, while the same specimens but
with short pre-cracks (and therefore with higher propagation
energy and velocity) cleave along the inclined
(1 1 1) plane. The same specimens with intermediate
pre-crack length show that the crack first propagates on
the (1 1 0) plane and then deflects to the (1 1 1) plane.
We show that the deflection is due to variations of the
material property that resists cracking, , the dynamic
cleavage energy,with velocity and crystallographic orientation.
We propose selection criteria to explain the
deflection: The crack will deflect to the plane with the
lowest dynamic cleavage energy. We further suggest
that crack deflection is the basic mechanism controlling
the way the crack consumes energy while propagating
and is the main cause of surface perturbationsThe spatial temporal fracture energy along the (1 1 0)
cleavage plane is evaluated
