Brake Rotor FEA

[Rotarynut]

I'm in charge of designing the brakes for the 2011-2012 Formula SAE car. Recently, I dialed in all of my load calculations and started to work on brake rotor designs. I went to FEA a few of them in CATIA and ran into a few issues; The main one being I need help with figuring out how to "clamp" it.
I need to create an area on the friction surfaces the size and shapes of the brake pads that I can use as my "clamp" as I apply a moment to the wheel hub/brake rotor interface. I have tried projecting the profile of the brake pad into my part and then "padding" it out about 0.05" on either side of the rotor, but then CATIA just 'recognizes' it as part of the rotor and it creates insane stress risers around the area, and throws off my values significantly.
Using a design safety factor of 4, even with a solid, "blank" rotor to imitate what would be the "strongest" rotor would be, I am getting values that are double the max designed yield stress. When I start adding geometry to the rotor to reduce mass, and create a useable design, I am seeing values over 8 times my designed max stress.

Does anyone have a suggestion on how to set up a useable FEA for the brake rotor?

[Ben K]

Instead of creating a pad, what about creating a split line/surface? That way you break up the rotor surface as your "open" and "clamped" sections and you can apply the force properly.

Also--you could add rounds to your pads to try and remove the stress raisers.

Ben

[Der Krug]

We used SolidWorks FEA and created a split line.

[Rotarynut]

The split line doesn't work. It just joins the material together, as does pocketing it and then creating another pad in the pocket.

[Ben W]

0.05" is far too large and is within the resolution of the meshing tool. We use ANSYS Workbench, which as far as I know, lacks a splitline function. As I understand it, split-lines force a geometry or boundary in a mesh, so the mesh has to form to the shape that is defined. If you can't figure it out, or if your FEA package lacks one, try much smaller. I used 0.0001" and smaller for my FEA. This is small enough that the elements are magnitudes larger than the height of the pad. In effect, you are using the loss of geometry to your advantage.

[billywight]

I used 0.0001" and smaller for my FEA.

.0001" for element size? That's a bit small...

[Ben W]

.0001" for element size? That's a bit small...



That's what I found was required to force the mesh to outline the pads on the surface but not actually have a raised surface in the mesh.

[Rotarynut]

A better way to do it is to learn how to do an assembly FEA, which is what I ended up doing.