# bending test of a bulk

Hello,

I want to do bending test with periodic boundary condition in 3 dimensions ( boundary p p p ). I mean, I should do something like fixing one end and bending from the other end in Y direction. I haven’t found the “fix deform” useful. I need a command which applies force in e.g. positive direction of Y, not like the erate command that increases box size in positive and negative directions together.
Please introduce a useful command for the purpose.

Thanks a lot,
Soroush

Hi Soroush,

If I understand you correctly, "fix rigid" and "fix move" are your friends.

First group your bulk into three regions, two at each end and one in
the center. Use "fix rigid" to fix your center region, then use "fix
move" to assign two end regions with downward velocity. You may have
to change your boundary conditions to "p s p" or "p m p".

Best,
Ray

If the box is periodic, what does it mean to bend the box or the
atoms at one end?

Steve

i know it does not have correct concept. But i have tested bending a bulk by deform command. But it wa not useful. deform command does not do bending!
would you please tell me the correct way?
Thanks

Hi,

There is actually an article that explain a way to bend the computanional box:
"Torsion and bending periodic boundary conditions for modeling the
intrinsic strength of nanowires" Wei Cai , William Fong, Erich Elsen,
Christopher R. Weinberger

http://micro.stanford.edu/~caiwei/papers/Cai08jmps-torsionbending.pdf

I'm trying to understand the article , but my brain power is low ...=(
Oscar G.

Thanks a lot, Oscar.
I will try to understand it.

Hi,

There is not actually a correct way (correct me if i'm wrong)... I'm
also working on the bending of materials, and the way i do it is
is somewhat of a bruteforce method i,e applying a force "F" at the
free end (cantilever beam problem). Using the aftermentioned method
you may be able to observe large deflections and observe the plastic
behavior, but unfoutounately the calculation of the later stiffness
(flexural moment) is not something trivial (I found There are 3
methods which might help in obtaining the calculation)

Oscar G.