- [Instructor] Now we're continuing from the previous video.
We're going to run the analysis for the mesh
created from the solid body geometry.
The first thing we want to do is
to suppress the vertical loading,
and we'll just run the horizontal loading.
So run this study.
Now under the stress one result, we have the X normal.
Let's right-mouse click that, edit definition.
Let's look at the top level stresses, check OK.
Now if we go to plot tools, probe, select an element
in the center region, we get a peak stress of 2,490.
It varies slightly, but it's around about that value.
And that's obviously incorrect.
Check OK, let's change the sense of the stress again.
So go to the edit definition,
this time we want to look at the bottom stress.
Check OK, and we can come to plot tools, probe.
Pick any of the elements in the central region.
We're getting a stress of around 4,989 PSI,
a small variation, but similar kind of number.
Again, that's incorrect,
compared to the previous answers we've had.
Check OK, under stress one, let's edit the definition again,
and we can choose membrane stress.
Check OK, and if we use the plot tools again, probe,
pick any element in the central region,
we're getting 1,250 PSI,
which is the correct value for membrane.
Check OK, let's repeat the process.
Right-mouse click, edit the definition, this time,
just look at the bending component to the stresses.
Again, go to plot tools, probe,
choose some elements in the center.
We can see here, we're getting a value of around about 3,737
as a stress due to bending,
which is obviously incorrect, it should be zero.
So what's happening here is that
the shell elements are picking up a load offset,
due to the misalignment of the virtual plane of the elements
with the line of action of the applied load
and the subsequent reaction through the nodes.
And if we do a hand calculation, it confirms
the spurious bending stress is theoretically 3,750 PSI,
which is the value that we were seeing.
In an earlier video,
I've given a detailed explanation of this.
Now let's change our loading state by unsuppressing
the vertical load and suppressing the horizontal load.
Let's rerun the analysis.
Let's right-mouse click on stress one, edit the definition,
and we want to look at the top surface stresses.
Check OK, now the peak value at the root here
is shown from the legend to be roundabout 33,780.
If we change this to the bottom surface,
edit the definition, change to bottom, check OK,
now we can see in this region,
we're getting roundabout 33,560 in tension.
So this ties up very closely to the pure bending
stress levels we saw in the previous exercise.
Another way to show this is by going again to stress one,
editing the definition, now we choose the advanced options
and we render shell thickness in 3D.
Notice the top grays out,
because we're going to be seeing top and bottom together.
So we check OK, now we can see clearly
the maximum and minimum is close to plus or minus
the same values, so it's 33,560 and minus 33,780.
Come back to our normal plot by switching off the 3D render.
So the model only has very small areas here,
due to the outer plane loading,
the offset isn't playing a role.
So in conclusion, in this video,
we've seen the implication of using shell elements
created from surfaces on a solid body geometry.
Using shell offsets gives a virtual position
of the shell mesh.
The loading is still applied through the physical nodes,
and that gives us this moment.
So any axial loading will create a spurious moment.
The resultant additional bending stresses
add to the correct membrane stresses.
If we apply loads normal to the plate,
then they will only result in bending stresses
and those will be correct.
In the next video, we'll look at the third
of our three methods to create shell meshes
by looking at the sheet metal part approach.
And now we'll save off the model,
and we'll save as offset_plate_end.
And we'll save there, and we'll copy the results.