Structural constraints

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Structural constraints.

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In this video, we will review structural constraints.

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We will create a fixed constraint pin constraint and a bolted connection.

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In Fusion 360, we want to carry on with our motorcycle rear set.

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At this point, we've taken a look at our materials.

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We've defined the materials and we've even created a custom material for our steel bracket.

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But now we want to talk about constraints.

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If we expand the constraints, we have three options.

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Structural constraints which allow us to create fixed or pin constraints as well as a few others,

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that define how our components or bodies are related to their environment.

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We also have a bolt connector and this is used to create a connection between two bodies that represent the bolts or hardware.

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These will be done mathematically and there will be a graphical preview on the screen,

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but this allows us to avoid having solid mesh elements to represent that hardware.

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And the last is a rigid body connector.

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This is not one we will be exploring in this course, but there are two different types of rigid body connectors,

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that can be used to represent a fixed or rigid connection between a vertex on one body and multiple vortices on another.

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For our example, let's get started by going into structural constraints.

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First, we're going to explore the fixed constraint type.

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We're going to select our targets as the faces where the socket head cap screws are going to hold this bracket down to the motorcycle.

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From here, if we simply said, okay, what we've told Fusion 360 is that these faces can't move or translate in X, Y or Z.

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When we're thinking about how to set up our structural constraints we need to realize how they are actually constrained in the real world.

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In our case, if we take a look at our coordinate system,

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the X direction is the direction in which the bolt head is going to be holding down this bracket to the frame.

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So the way that I'm going to set this up is by deselecting Y and Z.

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You'll notice that the icon is now an open lock icon.

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If we have all three fixed down, it's a closed lock icon.

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What we've now told Fusion 360 is that these faces cannot move in the X direction but they are still free to move in Z and Y.

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This is exactly how the bolt head would be holding down the face of this part.

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We're going to say ok and now we've created our fixed constraint but that still doesn't mean that our bodies are fixed in space.

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We need to go back to our structural constraints and the next one we're going to take a look at is a pin constraint.

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The pin constraint is going to be used on the inside area where the bolt or really the shoulder of a bolt is going to be holding this bracket.

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This also has three directions which we can control; radial, axial and tangential.

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We're going to deselect the last two options and only focus on radial.

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This will prevent the hole in this case the bolt hole from moving radially and it also prevents it from deforming radially.

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This is to better represent the fact that there is a bolt or a shoulder inside of that hole.

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This is now telling it that this face is going to be fixed in X,

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and the inside hole or the portion where the bolt is going to go through is now fixed radially.

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One thing that we have to understand is at this point the entire bracket is still free to rotate about that point.

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If we were to fix the tangential direction, this would prevent rotation, but in reality if we just simply had one bolt,

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it would still allow this bracket to rotate, assuming that we overcame the friction or the torque that's applied on the hardware.

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So we want to select both bolt holes; the upper and lower.

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And now we've told it that neither one of those can move radially,

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and the faces where the bolt heads are are going to prevent it from moving out in the X direction.

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If we now take a look at our degrees of freedom, you can see that the bracket is potentially fixed.

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It's not fully fixed because we haven't completely locked down all degrees of freedom.

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But the degrees of freedom that we applied are keeping it from moving around.

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If we instead went into our load case and back to our pin constraints and we modify them,

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and we make sure that we restrict the axial direction in just one of those and take a look at the degrees of freedom,

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you'll note that that hasn't changed anything and this is because the fixed constraint on the outside face is telling it that this face can't move.

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The axial direction on the pin constraint is not really providing any additional degrees of freedom.

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However, if we lock the rotation down on both of these pin constraints, we tell it that neither one of those can rotate.

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You'll see that simply having that locked rotation is not fully fixing it either.

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In order to completely fix something in 3D space, we need to lock down all degrees of freedom.

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However, in reality that's not how this bracket will be set up.

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So let's return to only a radial option because there's another option when we set up our simulation study,

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that's going to allow us to negate those rigid body movements by including some external dampers and some additional inertial reliefs.

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But now we have to consider what happens with this bracket.

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This bracket is in reality bolted to our frame mount but we really didn't have a way to create a constraint that held those two together.

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The first thing that I want to do is go into simplify and I'm going to clone my bracket and frame mount so right click and select Clone Simulation.

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We're going to bring in the study as well.

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And what we've done is we've created a second simulation that's exactly identical to the first.

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I'm going to rename my simulation and I'm going to say bolted bracket and frame mount.

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Now that we have that, we can finish simplify and take a look at how our browser has changed.

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We have our original simulation study which is our bracket and frame mount and then we have a study 1 static stress inside of there.

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But then we have our second or clone simulation model which is identical at this point,

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but it has our constraints that have automatically been applied because we cloned everything.

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Now we want to take a look at creating a bolted connection between the two.

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In order to do that, I'm going to select constraints and bolt connector.

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First, the location of the bolt head.

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You'll notice in this instance, we aren't able to select the tapered face,

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that the bolt head is not able to use a face selection, we have to select an edge.

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And because this edge is actually cut off slightly by the fillet, the only option we have is to select the edge here.

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We can use the option to have a threaded hole or with nut.

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In this example, I'm going to use with nut and select the back face,

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noting that we're getting a graphical preview on the screen showing the head of the bolt and the nut on the back side.

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From here, we also can select some options such as pre load, whether it's an axial or a mount or a torque that's applied.

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We can modify the units, for example an inch pound or foot pound and then we can have this value.

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In this case, I'm going to say that this bracket is torqued down with 20 foot pounds.

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You also can see that we can modify the material properties.

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By default, it's bringing in the material properties of the bracket but we can change these to any other material.

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For example, if we wanted to just use plain steel.

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For this example, I'm going to continue on using that high strength structural steel and then I'm going to say Ok.

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We need to repeat the process and use the bolt connector on the other bolt hole as well.

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Once again we're going to select the edge, we use with nut for the backside and select the back face, rotate back around to Home view,

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and we'll set up our torque exactly how we did on the first one.

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We'll change our units and we'll set it to 20 foot pounds.

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Once we have this set, let's take a look at our degrees of freedom.

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The degrees of freedom have made the entire bracket potentially fixed.

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If we go back to our original and we take a look at our degrees of freedom, you can see that this bracket is completely free.

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It has no relationship to our frame mount at all because we don't have a bolted connection and we haven't told it how the two are going to interact.

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So it's important to identify and understand the differences between creating that bolted connection,

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and what that connection actually means between the two components.

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We are going to end up solving three different simulation studies.

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We're going to solve the simulation study with the bolted connection.

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One that has what's called a bonded contact,

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and the last one that's going to be just our frame mount and it's not going to look at this bracket at all.

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So for right now, let's make sure that we do have our studies saved.

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It's going to be our bolted bracket and frame mount as well as the bracket and frame mount.

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Make sure that this is saved and then we can move on.