Hi!

The fracture tougness for different crystal directions in silicon can
be found for example in P.B Hirsch et al. "Dislocation dynamics and
the brittle-ductile transition in precracked silicon" G Michot et al.
"Fracture and crack tip plasticity in silicon and gallium arsenide"
both in Proceedings of the Sixth Int. Symp. on Structure and
Properties of Dislocations in Semiconductors, 1989, Oxford

In the (110) direction a values around Kc=0.9 MPa.sqrt(m) are given.

C. Marxer
imt, University of Neuchatel