Changing the way the stress is calculated gives more realistic results - my assumption regarding Hooke's law was perhaps invalid.

On Mon, Feb 7, 2011 at 3:37 PM, Andre Smit wrote:
Robert

I'm having problems relating the model's output to the actual test output. One issue that is confusing is that if I reduce the displacement interval from 0.001 to 0.0001, say and the time during this interval to ensure a consistent loading rate, then the results change significantly, both the maximum load at failure and the displacement at maximum load. This is unexpected. I can't think what the problem can be - any ideas on your side?

On Wed, Jan 26, 2011 at 10:50 AM, Robert Cimrman wrote:

Ok, interesting. Well, I cannot help you much at this point :)

You might want to try a finer mesh, just to compare with the current one...

r.

On Wed, 26 Jan 2011, Andre Smit wrote:

I think the iterations are indirectly sorting this out. In fact I found
that the initial stiffness(0) doesn't influence the results at all. I've
attached results of compression (comp) and tension (tens)  tests at rate
of 1mm/sec as well as the script in its current state. Based on lab
tests, comparative compression failure at this rate occurs at 6.6 N/mm2
whereas tension failure occurs at 3.0 N/mm2. So the script is accurately
predicting compression failure but under-estimating tension failure.
Still exploring ...

a

On Wed, Jan 26, 2011 at 10:19 AM, Robert Cimrman <cimr...@ntc.zcu.cz>
wrote:
Well, this flag is used essentially only in the generic
solver used by simple.py. In the strain rate solver script we
solve every time step regardless this flag.

The first time step is different, however, as strain equals
strain0 (no previous strain defined), and so initial dstrain
is zero. Maybe this causes some problems?

r.

On Wed, 26 Jan 2011, Andre Smit wrote:

Alright, that fixes it! Now I understand the reason for
quasistatic! In
the non-linear analyses, the time stepper is set
programatically - is is
possible to force solving for the first time step here
as well as in:

for ii, disp in ds:
#my_output(dformat % (ii + 1, ds.n_step, disp))

force0 = 0.0

pb.ts.is_quasistatic = True  # <<<===========
Force quasistatic
pb.time_update(ts)

On Wed, Jan 26, 2011 at 9:57 AM, Robert Cimrman
<cimr...@ntc.zcu.cz>
wrote:

So the problem is the single dot outside the
linear curve,
right?

What if you add

'quasistatic' : True,

to the time-stepper options? As it is now, the
first time
step is not solved but taken from the initial
conditions
(unspecified = zero) and boundary conditions
(nonzero!), so
it is not in equlibrium!

r.

On Wed, 26 Jan 2011, Andre Smit wrote:

Sorry - forgot to attach the figure - your point is
taken re
the nodal
residual. Forces are calculated and summed on each of
the
nodes in the
Top region. I checked this a while back and plotted in
Paraview - the
forces are zero at the other nodes within the model but
equal
and
opposite in direction to the Top at the corresponding
Bottom
nodes of the
model (as you'd expect).

a

On Wed, Jan 26, 2011 at 9:26 AM, Robert Cimrman
<cimr...@ntc.zcu.cz>
wrote:
Where can I see the line? maybe you forgot to
attach a
figure?

As for the forces, it might be better to compute
them
using a
(inner) surface integral of stress instead of the
nodal
rezidual. Btw. you look at the nodal force in the
first
node
of the Top region only, right? What are the values
in
the
other nodes?

r.

On Wed, 26 Jan 2011, Andre Smit wrote:

Thanks Robert!

I've attached a modification that shows the
strain/stress output for the
elastic case of the cylinder under
compression.
The slope of the line is
Young's modulus as you'd expect. As with our
non-linear analyses, the
forces calculated after the first time step
appear to be too high - not
sure what the reason for this is.

On Wed, Jan 26, 2011 at 2:25 AM, Robert
Cimrman
<cimr...@ntc.zcu.cz>
wrote:
There was some old code in the
stress_strain() function. The
exception was caused by putting
directly the
traction
function into the EBC definition,
its name. The
attached file should work.

r.

--
You received this message because you are subscribed to
the
Groups "sfepy-devel" group.
To post to this group, send email to
To unsubscribe from this group, send email to
For more options, visit this group at

--
Andre

--
You received this message because you are subscribed to
the
"sfepy-devel" group.
To post to this group, send email to
To unsubscribe from this group, send email to
For more options, visit this group at

--
You received this message because you are subscribed to
Groups "sfepy-devel" group.
To post to this group, send email to
To unsubscribe from this group, send email to
For more options, visit this group at

--
Andre

--
You received this message because you are subscribed to
"sfepy-devel" group.
To post to this group, send email to
To unsubscribe from this group, send email to
For more options, visit this group at

--
You received this message because you are subscribed to the Google
Groups "sfepy-devel" group.
To post to this group, send email to sfepy...@googlegroups.com.
To unsubscribe from this group, send email to
For more options, visit this group at

--
Andre

--
You received this message because you are subscribed to the Google Groups
"sfepy-devel" group.
To post to this group, send email to sfepy...@googlegroups.com.
To unsubscribe from this group, send email to
For more options, visit this group at

--
You received this message because you are subscribed to the Google Groups "sfepy-devel" group.
To post to this group, send email to sfepy...@googlegroups.com.
To unsubscribe from this group, send email to sfepy-devel...@googlegroups.com.
For more options, visit this group at http://groups.google.com/group/sfepy-devel?hl=en.

--
Andre

--
Andre