Static Stress Analysis of Connecting Rod Assembly Tutorial Difference in Results

[dvdsnyd]

Hi,

My name is Dave Snyder, this is my first post here. I have a couple questions regarding static stress simulations.

I am going through the static stress simulation tutorials, specifically the connecting rod assembly example.

When it came to trying to solve the problem, I couldn't solve it locally. I received an error. in my solution. I couldn't get my results. I read somewhere that people had success with reinstalling Fusion. I did this, and this time around, the solver sat at 1% for about 15 minutes. I finally cancelled, and solved it in the cloud.

My computer is a bit dated, but was a mid-high range computer about 5 years ago Other than this issue tonight, I haven't had any issues running Fusion. Any thoughts on what could be going on with local solutions?

The second part of my questions come from differences in the solution compared to the given answer in the tutorial. I also receive a warning about the safety factor being under 3. The differences can be seen in the attachments. Most notably:

My Results for Von Mises stresses:

Max - 20772 psi

Min - 67.8 psi

Expected Results:

Max - 21653 psi

Min - 46.82 psi

There isn't a huge difference, but it's large enough for me to question and want to try to understand before I start to apply this to my own applications.

I really appreciate any and all help with this. Please let me know if I can provide any more detail!

Thanks,

Dave

[ahreum.ryu]

Hi @dvdsnyd, 

Welcome to the Fusion 360 community!!

Regarding the Local solving issue, Have you seen this article?  Unable to successfully run local solve analysis within Fusion 360

Regarding the different result, I have recorded following instructions, and I got the similar result as expected. Would you mind taking a look at that? could you let me know if you find something else?

http://autode.sk/2wXB3Kc

And please find attached the model file. Hopefully this will help 

Many thanks, 

Ahreum. 

[dvdsnyd]

HI @ahreum.ryu

I was able to locally solve your provided file on my machine. It just took a little longer than I was anticipating. I did get the same results as you showed. However, the results are off from the example.

Again, the example solves to:

Max stress - 21653 Psi

Min stress - 46.82 Psi

The results from your analysis are:

Max - 21750

Min - 43.51

The minimum stress is not in the correct location compared to the example.

I went through the tutorial once more. I noticed that in step 10/29 of the guide. The guide says to click on two edges. The model that I downloaded had 3 edges. I noticed this in your model as well. Not sure if this would affect things?

I was able to once again locally solve and I obtained the same results as the results I reported on in my first post.

The results are close, but again, I am troubled that they differ from the tutorial. Any help in understanding why would be greatly appreciated!

Thanks,

Dave

[dvdsnyd]

Hi @ahreum.ryu

Have you had a chance to look at my response?

Thanks for all your help!

Dave

[TheCADWhisperer]

What are your mesh settings?

Have you run a convergence analysis?

Export and attach your *.f3d file here.

[dvdsnyd]

Hi @TheCADWhisperer

Thank you for taking a look into my problem!

I have attached the .f3d file where I ran through an adaptive mesh study. (as well as a file where I did not)

The convergence plot definitely tells the story of some singularity issues within the model as shown below.

This all came about by just trying to go through the Autodesk tutorial found on the learning site. for simulation.

The tutorial doesn't mention any sort of adaptive mesh or convergence.

I would expect that I should be able to get the same result as the tutorial.

I really appreciate any and all help!

Dave

[ahreum.ryu]

Hi @dvdsnyd,

Sorry for the late response.

Fusion 360 option has changed a lot since release. As of now, we don’t know which convergence values the tutorial uses. We would have a different result following the convergence option.

I would like to explain about the convergence. For example, if you set the convergence as 5%.

1st results = 22000 (range of 5% = 1100)

= the 2^nd result should be within 20900 or 23100 (but 2^nd result is over 23100)

2^nd result = 24626 (range of 5% = 1231.3)

= 3^rd result should be within 24626+1231.3= 25857.3 (+/- possible)

3^rd result = 25525  

= 3^rd result is within 5% average, so it stopped.

In FEA, a finer mesh typically results in a more accurate solution. However, as a mesh is made finer, the computation time increases so we should find appropriate mesh. 

I have changed the convergence options, and this is the result below.

Along with the Refinement option, the result and mesh have different values and runtime. Therfore I would like to say we should find the satisfied values between running time and results. 

For your reference,

This is help of Adaptive Mesh Refinement: http://help.autodesk.com/view/fusion360/ENU/?guid=GUID-9AA69E6D-F278-4E40-AEFD-AEE1BDA97957

Understanding Singularities: https://www.autodesk.com/products/fusion-360/blog/quick-tip-singularities-and-simulation/

If you have further questions, please let me know

Many thanks,

Ahreum.