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Transcript
00:08
In this exercise, we will be assigning and working with Enforced Motion Loads.
00:15
In this exercise, we'll be working with this thin sheet metal bracket.
00:19
I have created it as a surface shape.
00:22
So, it's just a non-dimensional surface.
00:25
And that means I'm going to create an idealization for it using shell elements.
00:30
So, if I open up, I would ask Inventor Nastran, you'll notice I've already created a shell idealization here.
00:36
Shell number 1.
00:38
If I edit that idealization, you will see that it is tenth of an inch thick.
00:43
Aluminum 6061 idealization.
00:46
And it has been meshed with an element size of 0.05 inches.
00:51
So, it's a fairly fine mesh to start with.
00:53
And that will give us good results when we start to generate a couple of studies.
00:58
So, we'll be using a new load type called enforced motion in this study.
01:03
The way that enforced motion works is essentially we're going to be moving the mesh a specific distance.
01:09
It can also be what's called constrained motion.
01:13
And due to the fact that we are moving the mesh, we'll actually need a constraint to be added in the same direction as the motion.
01:21
So, to apply this first, I'll go to loads and I'll start by adding in my enforced motion.
01:28
So, if I go to the type here and I drop down to enforced motion, what you'll notice is the magnitude now for the X, Y and Z direction,
01:36
is the Tx meaning translation in the X, Y and Z, and the magnitude is in inches.
01:43
So, if I select the entity, I'd like to move.
01:46
In this case, I want to move the edge at the end of the plate here up a given distance,
01:52
and then calculate the stresses and the reaction forces that are created as a result of that motion.
01:58
In other words, I want to see when I bend this plate, a given amount.
02:04
Will my structure yield and ultimately, how much force does it require to move the plate that far?
02:12
So, it's a very useful tool because you're basically doing the FEA in reverse.
02:16
You may not know the force required to create that movement, but you may know the end result due to physical testing or prior analysis.
02:24
So, what I can do is for Tz I'll type in an eighth of an inch, 0.125.
02:31
And if I activate the glasses here, you'll see this cylinder added to the end of the line that is the icon for enforced motion.
02:38
So, I'll rename this.
02:48
So, I know exactly what it is when I take a look at my subcases.
02:51
So, I'll select "Ok", that's been added in to subcase number 1.
02:56
On the same edge in the same direction as the motion, I need a constraint.
03:03
So, if I go to constraints, I don't need to change the type, it's still a structural constraint.
03:09
But what this does is it allows the motion to move the constraint which ultimately moves the mesh.
03:15
So, it's one additional step that's required for these types of studies.
03:19
So, if I select the same edge, I don't need a fixed constraint, all I need is a constraint in that same planar direction, which is the Z direction.
03:29
So, I'll click "Free".
03:30
And then I'm going to go ahead and check the box for Tz which means I'm constraining motion in the Z direction, the direction of the displacement.
03:37
And I'll rename this EM Constraint.
03:40
So, I know that it's the enforced motion constraint.
03:44
I'll select "Ok".
03:45
And now I'm ready to add in my normal constraints and I can solve the study and extract the stresses and reaction forces.
03:56
So, for the remaining structural constraints,
03:58
I'm going to fix the two-hole locations that will be bolted to an adjoining component that's not modeled here.
04:05
So, I will go to constraints and I'm just going to go ahead and rename this Hole 1.
04:12
So, I'll create two separate constraints that way I can keep track of each of them individually.
04:16
So, I'll select the top hole here and I'll hit the little glasses so I can see that it's been added and then I'll select "Ok".
04:23
And I'll click "Constraints" again and I will rename this one "Hole 2".
04:28
Both of these will be fully fixed in this case.
04:31
So, I'll select the lower hole now, rename it Hole 2.
04:34
All of the degrees of freedom are accounted for and I can select "Ok".
04:39
And now I have my enforced motion constraint and that is going to be added on the same location as my enforced motion.
04:46
And then I have Hole 1 and Hole 2, which are both fixed constraints.
04:49
So, I can now save this.
04:51
And I'm ready to solve and identify what stresses come as a reaction from this enforced motion.
04:57
So, I'll select "Run".
05:04
So, we'll solve. It's going to look just like any other linear static analysis.
05:08
Keep in mind you can use this enforced motion for things like transient studies and impact analysis as well,
05:14
if you'd like to or even a nonlinear transient.
05:17
In this case, we are using it just for a simple static.
05:21
So, after it solves, I can then see the stress is about 10,000 PSI on this first hole edge here as you would expect,
05:28
that's where most of the stress will be located is that first upper hole there as a result of the moment being created from that offset load.
05:37
So, what's happening is I'm moving the actual mesh exactly eighth of an inch.
05:42
So, if I go to displacement, you'll see 0.1264, sometimes you'll get a slight variation from the eighth of an inch because it's moving that edge,
05:50
but the ends might curl up a little bit more either way it should be right around that magnitude that I specified.
05:57
And then when I look at these stresses, I now know if I saw that much bending, what I can expect to see for Von Mises.
06:07
Now, the other way this is useful is I can calculate the reactions like I normally would.
06:12
So, I can go to hole 1 and right click on it and go to reactions like we have in prior exercises.
06:18
And now I can see the amount of force and the amount of moment that's being transferred to that upper hole.
06:26
Now, the other thing I can do is if I'd like to identify how much force is required to move this edge, that eighth of an inch,
06:35
I can do that by looking at the reactions on the enforced motion constraint.
06:40
So, I'll right click on that and go to "Reactions" and it says about 2 pound-force.
06:44
What this is saying is if I apply a load of 2 pound-force in the vertical direction to that edge, it should displace an eighth of an inch.
06:52
So, now I could work it either way.
06:54
But now I know that value I can use that for design purposes for setting limits or meeting requirements.
07:03
What I can also do is I can look at a second subcase where I might have bending or displacement in a different direction.
07:09
Let's say that we want to look at bending in the X direction this time.
07:14
To do that, I can just right click on "Subcases" and create a new subcase.
07:18
What I want to do is keep the constraints that are still useful, which is basically Hole 1 and Hole 2.
07:23
The other two options here for boundary conditions, I do not need to bring over to Subcase 2.
07:29
So, I'll select "Ok" to copy those over.
07:32
I'll then create a new load that will only be applied to Subcase 2.
07:36
So, I'll select "Subcase 2", deselect "Subcase 1".
07:40
And this will be 1/8" Horizontal Displacement.
07:48
So, you can name it whatever you want, but give yourself some clarification on what you're doing.
07:53
This time, I'll change my load type to enforced motion like I did before.
07:57
I'm going to select the same edge as I have before.
07:60
But this time my magnitude is going to be an eighth of an inch in the positive X direction.
08:06
So, you'll notice a new cylinder comes on here that is facing the X positive direction that will give me a new load.
08:12
So, again, make sure Subcase 2 is selected.
08:15
Select "Ok".
08:16
And now in Subcase 2, you'll see horizontal displacements been added.
08:20
I can also rename the subcases if I'd like to.
08:22
So, my first one, I could rename Vertical.
08:25
That way it's clear what the results will show.
08:28
And then Subcase 2, I'll rename Horizontal.
08:35
Now I need one more thing.
08:36
I need that constraint in that horizontal X direction or else this will not work properly.
08:42
So, I'll go to "Constraints", select "edge<8>", change the Subcase to be the Horizontal subcase.
08:50
I can rename this EM Constraint.
08:54
Once again, I could even put in EM Constraint 2.
08:57
So, I know it's a different one and I'm going to select "Free".
09:00
So, it's a free constraint and then check the box for Tx.
09:04
That's the only direction I need to constrain for that specific motion.
09:08
So, I'll select "Ok".
09:10
So, now I have a new horizontal subcase with a horizontal displacement Hole 1, Hole 2,
09:15
and then a new enforced motion constraint that's been added and I can go ahead and select "Run".
09:21
And what will happen is it'll solve this once again,
09:23
but I'll get two result sets this time one for the vertical eighth of an inch, the other for the horizontal eighth of an inch.
09:31
So, it's going to display that first and you can kind of see here a little more stress, right?
09:35
So, I'm getting about 18,000 psi whereas vertical, I was only getting about 10,000.
09:41
If I look at the enforced motion constraint.
09:43
You'll also see that it requires up to about 5.5 pounds of force to create that eight inch displacement.
09:51
It only required a couple of pounds to create that vertical displacement.
09:55
So, as you'd expect, this is going to be a little bit stiffer in the horizontal direction that it is in the vertical direction due to its geometry.
10:03
But again, this is a great way to work backwards to calculate the required force, to do something to your structure or your assembly.
Video transcript
00:08
In this exercise, we will be assigning and working with Enforced Motion Loads.
00:15
In this exercise, we'll be working with this thin sheet metal bracket.
00:19
I have created it as a surface shape.
00:22
So, it's just a non-dimensional surface.
00:25
And that means I'm going to create an idealization for it using shell elements.
00:30
So, if I open up, I would ask Inventor Nastran, you'll notice I've already created a shell idealization here.
00:36
Shell number 1.
00:38
If I edit that idealization, you will see that it is tenth of an inch thick.
00:43
Aluminum 6061 idealization.
00:46
And it has been meshed with an element size of 0.05 inches.
00:51
So, it's a fairly fine mesh to start with.
00:53
And that will give us good results when we start to generate a couple of studies.
00:58
So, we'll be using a new load type called enforced motion in this study.
01:03
The way that enforced motion works is essentially we're going to be moving the mesh a specific distance.
01:09
It can also be what's called constrained motion.
01:13
And due to the fact that we are moving the mesh, we'll actually need a constraint to be added in the same direction as the motion.
01:21
So, to apply this first, I'll go to loads and I'll start by adding in my enforced motion.
01:28
So, if I go to the type here and I drop down to enforced motion, what you'll notice is the magnitude now for the X, Y and Z direction,
01:36
is the Tx meaning translation in the X, Y and Z, and the magnitude is in inches.
01:43
So, if I select the entity, I'd like to move.
01:46
In this case, I want to move the edge at the end of the plate here up a given distance,
01:52
and then calculate the stresses and the reaction forces that are created as a result of that motion.
01:58
In other words, I want to see when I bend this plate, a given amount.
02:04
Will my structure yield and ultimately, how much force does it require to move the plate that far?
02:12
So, it's a very useful tool because you're basically doing the FEA in reverse.
02:16
You may not know the force required to create that movement, but you may know the end result due to physical testing or prior analysis.
02:24
So, what I can do is for Tz I'll type in an eighth of an inch, 0.125.
02:31
And if I activate the glasses here, you'll see this cylinder added to the end of the line that is the icon for enforced motion.
02:38
So, I'll rename this.
02:48
So, I know exactly what it is when I take a look at my subcases.
02:51
So, I'll select "Ok", that's been added in to subcase number 1.
02:56
On the same edge in the same direction as the motion, I need a constraint.
03:03
So, if I go to constraints, I don't need to change the type, it's still a structural constraint.
03:09
But what this does is it allows the motion to move the constraint which ultimately moves the mesh.
03:15
So, it's one additional step that's required for these types of studies.
03:19
So, if I select the same edge, I don't need a fixed constraint, all I need is a constraint in that same planar direction, which is the Z direction.
03:29
So, I'll click "Free".
03:30
And then I'm going to go ahead and check the box for Tz which means I'm constraining motion in the Z direction, the direction of the displacement.
03:37
And I'll rename this EM Constraint.
03:40
So, I know that it's the enforced motion constraint.
03:44
I'll select "Ok".
03:45
And now I'm ready to add in my normal constraints and I can solve the study and extract the stresses and reaction forces.
03:56
So, for the remaining structural constraints,
03:58
I'm going to fix the two-hole locations that will be bolted to an adjoining component that's not modeled here.
04:05
So, I will go to constraints and I'm just going to go ahead and rename this Hole 1.
04:12
So, I'll create two separate constraints that way I can keep track of each of them individually.
04:16
So, I'll select the top hole here and I'll hit the little glasses so I can see that it's been added and then I'll select "Ok".
04:23
And I'll click "Constraints" again and I will rename this one "Hole 2".
04:28
Both of these will be fully fixed in this case.
04:31
So, I'll select the lower hole now, rename it Hole 2.
04:34
All of the degrees of freedom are accounted for and I can select "Ok".
04:39
And now I have my enforced motion constraint and that is going to be added on the same location as my enforced motion.
04:46
And then I have Hole 1 and Hole 2, which are both fixed constraints.
04:49
So, I can now save this.
04:51
And I'm ready to solve and identify what stresses come as a reaction from this enforced motion.
04:57
So, I'll select "Run".
05:04
So, we'll solve. It's going to look just like any other linear static analysis.
05:08
Keep in mind you can use this enforced motion for things like transient studies and impact analysis as well,
05:14
if you'd like to or even a nonlinear transient.
05:17
In this case, we are using it just for a simple static.
05:21
So, after it solves, I can then see the stress is about 10,000 PSI on this first hole edge here as you would expect,
05:28
that's where most of the stress will be located is that first upper hole there as a result of the moment being created from that offset load.
05:37
So, what's happening is I'm moving the actual mesh exactly eighth of an inch.
05:42
So, if I go to displacement, you'll see 0.1264, sometimes you'll get a slight variation from the eighth of an inch because it's moving that edge,
05:50
but the ends might curl up a little bit more either way it should be right around that magnitude that I specified.
05:57
And then when I look at these stresses, I now know if I saw that much bending, what I can expect to see for Von Mises.
06:07
Now, the other way this is useful is I can calculate the reactions like I normally would.
06:12
So, I can go to hole 1 and right click on it and go to reactions like we have in prior exercises.
06:18
And now I can see the amount of force and the amount of moment that's being transferred to that upper hole.
06:26
Now, the other thing I can do is if I'd like to identify how much force is required to move this edge, that eighth of an inch,
06:35
I can do that by looking at the reactions on the enforced motion constraint.
06:40
So, I'll right click on that and go to "Reactions" and it says about 2 pound-force.
06:44
What this is saying is if I apply a load of 2 pound-force in the vertical direction to that edge, it should displace an eighth of an inch.
06:52
So, now I could work it either way.
06:54
But now I know that value I can use that for design purposes for setting limits or meeting requirements.
07:03
What I can also do is I can look at a second subcase where I might have bending or displacement in a different direction.
07:09
Let's say that we want to look at bending in the X direction this time.
07:14
To do that, I can just right click on "Subcases" and create a new subcase.
07:18
What I want to do is keep the constraints that are still useful, which is basically Hole 1 and Hole 2.
07:23
The other two options here for boundary conditions, I do not need to bring over to Subcase 2.
07:29
So, I'll select "Ok" to copy those over.
07:32
I'll then create a new load that will only be applied to Subcase 2.
07:36
So, I'll select "Subcase 2", deselect "Subcase 1".
07:40
And this will be 1/8" Horizontal Displacement.
07:48
So, you can name it whatever you want, but give yourself some clarification on what you're doing.
07:53
This time, I'll change my load type to enforced motion like I did before.
07:57
I'm going to select the same edge as I have before.
07:60
But this time my magnitude is going to be an eighth of an inch in the positive X direction.
08:06
So, you'll notice a new cylinder comes on here that is facing the X positive direction that will give me a new load.
08:12
So, again, make sure Subcase 2 is selected.
08:15
Select "Ok".
08:16
And now in Subcase 2, you'll see horizontal displacements been added.
08:20
I can also rename the subcases if I'd like to.
08:22
So, my first one, I could rename Vertical.
08:25
That way it's clear what the results will show.
08:28
And then Subcase 2, I'll rename Horizontal.
08:35
Now I need one more thing.
08:36
I need that constraint in that horizontal X direction or else this will not work properly.
08:42
So, I'll go to "Constraints", select "edge<8>", change the Subcase to be the Horizontal subcase.
08:50
I can rename this EM Constraint.
08:54
Once again, I could even put in EM Constraint 2.
08:57
So, I know it's a different one and I'm going to select "Free".
09:00
So, it's a free constraint and then check the box for Tx.
09:04
That's the only direction I need to constrain for that specific motion.
09:08
So, I'll select "Ok".
09:10
So, now I have a new horizontal subcase with a horizontal displacement Hole 1, Hole 2,
09:15
and then a new enforced motion constraint that's been added and I can go ahead and select "Run".
09:21
And what will happen is it'll solve this once again,
09:23
but I'll get two result sets this time one for the vertical eighth of an inch, the other for the horizontal eighth of an inch.
09:31
So, it's going to display that first and you can kind of see here a little more stress, right?
09:35
So, I'm getting about 18,000 psi whereas vertical, I was only getting about 10,000.
09:41
If I look at the enforced motion constraint.
09:43
You'll also see that it requires up to about 5.5 pounds of force to create that eight inch displacement.
09:51
It only required a couple of pounds to create that vertical displacement.
09:55
So, as you'd expect, this is going to be a little bit stiffer in the horizontal direction that it is in the vertical direction due to its geometry.
10:03
But again, this is a great way to work backwards to calculate the required force, to do something to your structure or your assembly.
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