We wanted to do some rough simulation of our Polyoxymethylene (Delrin) bearings to determine if they can handle the pressure we expect under load! So,.. I learned how to operate SimScale over the course of the last week. Simscale is a rather easy to operate web-based mechanical engineering simulation program.

We compared our current prototype bearing profile with a hypothesized newer profile with potentially better stress relieving attributes.

Simulation #1) Current Bearing Profile. 1" Diameter.. Cut 1/4 off at the top.

Simulation #2) Hypothesized Profile. 1.25" Diameter.. Cut halfway through.

Polyoxymethylene--

Young's Modulus: 3.1*10^9 N/m^2

Density: 1,410 kg/m^3

Poisson's Ratio: 0.44

Applied force: 2,000 lbs Normal to flat face.

Constraints: Round support structure cradling bottom half of bearing

Notes: A majority of the strain appears to be forming above horizontal diameter.

Displacement [m]

Notes: Any surface area not supported is experiencing some displacement. This is a good argument for the half-ball rather than the full 3/4 ball we have now.

Cauchy Stress [Pa]

Notes: Cauchy stress indicates the stress experienced during displacement.

von Mises Stress [Pa]

Notes: Now this is the plot we're really interested in! The VM stress plot will tell us whether our bearing will break under load. The 1/4 cut 1" ball results in a peak VM stress of approx. 3,000 psi whereas the 1/2 cut 1.25" ball results in peak stress of approx. 2,000 psi.

Conclusion-- The compression strength of Delrin is approximately 5,000 psi. Our current setup may be getting a little too close to that number for comfort. Cutting the ball in half certainly reduces strain. Increasing the bearing size certainly increases our ability to disperse applied stress.