SW 2019 FEA Accuracy, Hertzian Contact between Parallel Cylinders.

[RodRico]

I'm designing a cam driven engine. I do all the calculations in Excel then export the results as equations to Solidworks where I create 3D models and run analysis to confirm my Excel calculations. The Excel calculations related to the most heavily stressed cam (R1 = 0.290", R2 = 2.468", 2,768 lbf force) indicate peak contact pressure of 248 kpsi over a contact length of 0.993" and width (2b) of 0.014" yielding Von Mises stress of 231 kpsi. The material is Maraging 350 steel having 319 kpsi yield, 0.32 Poisson Ratio, and 29,733 kpsi modulus of elasticity. I have confirmed my 2D calculations with several on-line calculators, so I'm confident they are correct. The 231 kpsi Von Mises result is, however, uncomfortably near the 319 kpsi yield.

When I run the same conditions in Solidworks FEA, I get a peak Von Mises stress of 213 kpsi. At first glance, that seems to correlate well with my 2D Excel result of 231 kpsi. Unfortunately, the Solidworks result reflects a hot element, and the rest of the surface shows a much lower Von Mises stress, typically below 138 kpsi. I extracted the stress and contact force data from the contact patch and confirmed it is a 3D Mohrs Circle calculation.

My question is simply this: Should I trust the Solidworks 3D results or my own 2D calculations when evaluating the design for margin?

 

[EngDesServices]

We typically have good results with Solidworks FEA, albeit it is annoying you can't specify the mesh type in the mesh control settings so that you can get away from tets. Personally, I would have simplified the model and done an analysis using Abaqus with a much higher degree of element control.

I personally use hand calculations to get an idea of what results I should expect before doing a simulation. If the results of the simulation are significantly different than what I calculated, I make sure I understand why before I proceed.

What boundary conditions did you apply for the results you've shown above? Do they represent the same problem you solved in excel?

To answer your question directly: If I were confident in both results and couldn't explain the difference, I would use the higher stress value that results in the lower margin.

Michael Hall, PE (TX) PMP - President
Engineering Design Services LLC

http://www.engdess.com

 

[hendersdc]

Have you already gone through the FEA setup to confirm that all your constraints, material properties, forces, and geometries are correct?

I assume this is a steady state analysis, any chance the parts are deforming enough that the contact area has significantly increased compared to your excel calcs?

My main gripes about solidworks FEA vs ANSYS are the lack of constraint options and mesh control.