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.

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.

Take a look at this thread:

https://forum.solidworks.com/forum/messageview.cfm?catid=82&threadid=7288&highlight_key=y&keyword1=friction

I believe the aspect you are neglecting is the effect of bending moment on the joint and the added friction this generates. Hence when you increase the joint dimensions, the bending moment is transfered to very small force couple and has negligble impact.

Let me know if you have any further questions.

Cheers,

Ian