- [Instructor] So at the end of this video you'll be able to
run a plane strain analysis and compare the results
against a full 3D model.
We're going to open up the file again.
Open.
And we have lug3d_lbc_end.
We click on the study tab.
We can see the loads and boundary conditions
we set up previously.
Let's just check and see the mesh is there.
Show mesh.
That was our starting point.
So now we go ahead and run this study.
You can see it's very fast, indeed,
compared to previous 3D work we've been carrying out.
Again, just to emphasize, that's the beauty
of the plane strain approach.
They're very cheap elements,
very, very quick to run.
At the moment we have the deformed results on,
so let's just switch that off.
We see the default stress date,
stress one von Mises is showing.
At the moment it's defaulted to newtons per meter squared
so let's go into stress one,
edit the definition,
and we want to change that to PSI.
Ane now the peak stress is 'round about
52 and a half thousand PSI.
Let's go further into that result control.
Let's edit the definition.
A couple things we want to do here.
We want to change the fringe options from continuous
to discrete.
Continuous is too much of a
photo elastic type of visualization.
It doesn't give us a good field for
what the stress distribution is doing.
So I'd always recommend using discrete.
If the default is, as we've shown here, continuous.
One of the first task would be
set it back to discreet.
And we also notice that the bottom of the wall
is effectively isolated, as we mentioned,
from the rest of the structure
because we've had to repeat the constraints
on this section and this section.
This basically is just connected to ground its,
no stress is passing through it.
There is no way unfortunately,
to delete unwanted pieces of geometry
from this automatically created section size.
That's one of the limitations of this approach
to plane strain analysis.
If we set up the geometry from scratch
then we could have the correct
kind of geometry we wanted.
Let's zoom in a little closer.
(clicking)
Look at that shoulder region.
We can see the very steep stress gradients
which are being implied there.
Now at the moment we have stress one,
which is von Mises.
What we'd really like to look at
is maximum principal stress.
von Mises stress includes all of the stress components
and what we really want to do
is look at stress flowing around here.
So, maximum principal stress
will tend to flow around the edges here.
So let's change the stress type here.
Go to edit definition.
We can simply change that to maximum
or first principal stress there.
Check okay,
Now we can see that in fact,
the maximum principal stress goes up to
around about 58 and a half-thousand or 58,640 there.
Now what we'd like to do is get a better idea
of the stress flowing around that particular region there.
You can see I've got a curve,
just highlight there.
I also have a curve here.
In the previous video we saw
a plot of the stresses round here,
and the stresses round here,
so we're going to replicate that kind of plot.
So let's choose that curve which forms the fillet radius.
And we go to plot tools
and we go to probe
and the probe tool
at location is the default
which would basically be picking off entities
such as different elements in here
what we want to do is probe onto
selected entities.
So now I can click on that curve,
shows up there.
And it's going to plot,
whatever stress state I have
included in here.
So the moment I have maximum principal stresses,
p1 stresses,
so that's what all we'll be plotting here.
So we click update,
and fills out this spreadsheet
which is basically picking off
every node running around that line.
Looking at the actual positions
and then it's also going to
turn it into parametric positions.
And then what I can come down here and do
is to click on the plot icon.
I've got a very nice plot showing,
a big stress running around here.
So, the end of the stress
is shown here,
the other end of the stress would be shown here.
The peak stress is somewhere in the middle.
Now the cursor's very useful
because it gives an indication
of what that peak stress is.
So we can look very exactly and say,
it's 58,000 or 58,400.
One thing to be careful of,
it's not actually picking up the data values,
it's dependent on your accuracy.
If you're good at shooting,
you can hit the target, you can hit the number.
So, if for example, my aim was poor,
then I end up down here 56,600.
So, be careful to make sure you pick that.
It's useful, but it can trap you a little bit.
In a report, this is a great way
to actually show peak stress.
So what I like to do,
is to show a plot exactly like that.
I would take a screen capture,
I would show the stress variation
on the contour plot,
and then show that very objectively,
what that curve actually looks like.
Now, just to complete the picture,
if we wanted to know the stress running along,
in the nominal stress region,
then again,
I can pick this point here,
this entity.
Got to be a little bit careful
'cause at the moment if I try and do a compound plot,
of now, two entities which are being picked,
I update that,
then it's plotting both,
against parametric distance,
which doesn't give me a very meaningful
plot at all
in fact it gives me an erroneous plot.
So we've got to pick one or the other.
So I'm going to clear the selections,
re-pick that edge there,
update,
click,
and now I can see the stress result.
Now it's pointing the wrong way round
in that, this is the nominal stress here
which is at the left hand end.
This is the peak,
which is just running into that fillet radius in there,
so let me just delete that for the moment.
There's a very useful command in here,
which is to flip the edge plot.
And if I do that,
I can now do the plot,
it's orientated nicer, the right way 'round.
So in the previous notes,
this is how I actually grab that screen capture
in the plot.
So, this is the nominal stressor we took to
about 12,000 PSI.
Stress in this region in here.
You can see the start of,
stress concentration,
and that's just beginning to pick up
just at that point there.
Now, the other X-Y plot hasn't disappeared
it's still there.
So I can actually have both
appearing at the same time.
So again,
that is the kind of compound picture I was producing
in the previous notes,
and that's exactly how I produced them.
So again, that's the nominal stress
peaking up to that point,
that point runs up to there,
in fact, this plot also needs to be flipped.
I'm not going to do that at the moment
but that point here
represents the point here.
That's the continuation,
there's the peak,
and there's the run out there
so that 30,000 or just under 30,000
would be occurring,
just at this point here.
So, armed with these two forms of plots,
we can get a nice picture
showing exactly what's happening.
For us the important point
and we emphasize this in the previous notes,
is the nominal stressor,
is 12,000.
And the peak stress here which is around about
58,000.
Is peak stress over the nominal stress
that gives us that stress concentration factor
we talked about.
I shut the first plot down.
Now just out of interest what we can do here,
we have several options,
we can control,
the plots quite carefully if we want to
to work those plots up in more detail,
and I can also print off this plot separately
if I want to.
If I want to store the data,
it's a slightly different approach.
To store the data, I have an option in here
to save, and that save will save to the clipboard
and then I can just cut and paste that
into an Excel Spreadsheet.
So for example if I wanted to do a
combined Excel plot of stressors running down this edge
and stressors running around that edge,
I can sort that out
in Excel,
I can go and actually grab the dimensions
here as well.
So I can export all that data
so I can do a more sophisticated assembly of a plot
in Excel.
So it give us a lot of control there.
So we'll shut down the probe result,
come back to full screen view of what we have
and at that point
let's save off our solid works model.
We're going to call this lug3d_analysis_end
and we do want to copy the results files into that database.
So, in conclusion,
we've seen the plane strain analysis allows us
to really swamp the model with plenty of elements
so it can give a very smooth and well converged
stress distribution state.
We've also seen how we can go in
and use the data probe,
as well as the contour plots
can emphasize more objectively
what the stressors look like
as they run around these curves using the X-Y plots.