# Joint dimensions for friction of coincident planar mate?

Question asked by Dave Kolacz on Mar 17, 2009
Latest reply on Mar 18, 2009 by Ian Hogg
Hello,
I made a simple model to try and understand the joint dimensions for friction in a coincident planar mate. It's left me more confused.

My model is just a .10 inch thick by 1.00 x 2.00 inch plate of aluminum (density of .10 lbf/in^3 so total weight is .020 lbf). I applied a .001 lb force to the .10 x 2.00 inch face. Gravity set to load the 1.00 x 2.00 inch face. Initially I set the friction to zero and got perfect results for accelleration, velocity, and displacement (as compared to hand calculations).

When I set the friction coefficient to .025 (to give half the acceleration as the frictionless case) I got strange results.
With coincident mate friction dimensions set to L=1, W=2, and R =2 the plate only moved about .050 inch and then stopped. I would expect some
"tipping" of the plate to cause less than ideal case results, but with the plate only being .10 thick this should not have had much influence.
I ended up increasing L and W to several hundred times thier actual size before getting reasonable results.

Can any body tell me what I am doing wrong?

How do L, W, and R relate to each other? Is L and W used (while ignoring R) for a rectangular surface (such as mine)? Is R used (while ignoring L and W) for a round surface?

Please help. This has really shaken my confidence in my ability to get useful results from any model.