I've published work on fracture strength of 50 um +/- silicon membranes,
about 4 mm or so in area.  See references 43, 47, and 51 at:

http://www.aquarianmicro.com/papers.html

I have found student ANSYS and ANSYS to be useful tools in predicting
accurately the stress in single crystal silicon membranes, with
complicated edge structures (fillets) as well as bosses.  The standard
membrane analytical equations in the texts by Timoshenko and di Giovanni
also do well, provided one uses an adjustment of the membrane deflection
parameters (in the linear and cubic terms).

You should also look at references by Chris Muhlstein at Penn State; the
JMEMS paper by Wilson and Beck; work by Stuart Brown; and references
therein.  Alissa Fitzgerald's PhD thesis from Stanford is also a very
good work to read and understand.  It is available through University
Microfilms in Ann Arbor, Michigan.  There are outstanding controversies
regarding the mechanism of the nucleation of fracture in single crystal
and poly-silicon, as well as the effect of early-onset fracture on the
mechanical resonance frequency of cantilevers.

Sincerely,

Albert K. Henning, PhD
Director of MEMS Technology
NanoInk, Inc.
215 E. Hacienda Avenue
Campbell, CA  95008
408-379-9069  ext 101
ahenning@nanoink.net

-----Original Message-----
From: Andrea Mazzolari [mailto:mazzolari@fe.infn.it]
Sent: Saturday, April 19, 2008 2:20 PM
To: mems-talk@memsnet.org
Subject: [mems-talk] Silicon fracture strength

Hi all,
i need to bend very thin (50um or less) silicon crystals. I'm looking
for information about silicon fracture strength in order to be able to
predict the maxium bending radius which can be achieved.
Any suggestion to some literature treating this topic ? I've tried to
search for it, but i've been not very lucky.