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Stress analysis on shaft -- deformation error

Stress analysis on shaft -- deformation error

Stress analysis on shaft -- deformation error

(OP)
Hi all,

I'm designing a shaft for a turbine and I need to know the stresses it will feel as the rotor assembly rests and accelerates on it.  As shown here, it's supported by two bearings on each end and the hub in the center will connect to rotor blades that will turn as air moves through a wind tunnel.



The end goal is to maybe hollow out the 1-3/8" shaft to minimize weight, but we need a stress analysis.  Here's a picture of the bare shaft in Pro/E. I can see grooves for snap rings.



I tried running a test in Pro/E's Mechanica, but encountered an error that I couldn't figure out (something about edges), so I moved to solidworks.  Here's what I did. First, I chose material (Al 6061) and applied constraints in the snap ring grooves because specifying the bearing locations proved difficult and I just wanted to see if I could get any analysis done first.  I chose a "hinged" constraint because I want the shaft to only rotate about its axis.  I applied this constraint (shown) at all four snap ring grooves.



I then applied a torsional load around the middle of the shaft where the hub would be connected. I also applied a weight force for the weight of the rotor assembly here.



So in the end, here's what the shaft with simulation specifications looks like.



Then I mesh and run it. I get 27.3% into the analysis before an error pops up saying "Deformation for this study is too large to be realistic..." (shown here).



Choosing to stop cancels the analysis and I don't know what to do. Choosing to continue makes the simulation run for a while. Yesterday, it finally ended and gave me an error about strain being > 25%, which is obviously not good. Today, it's been running for 22 minutes and nothing has happened. Weird.

So what am I doing wrong? What am I missing and what do I need to change. I'm open to all suggestions. Thanks a lot.

 

RE: Stress analysis on shaft -- deformation error

(OP)
EDIT: I just noticed the window. It popped up underneath something. Here it is. The study terminates when I click okay.

RE: Stress analysis on shaft -- deformation error

Suggest you add a roller element or fixed restraint to one end of the shaft, to eliminate/control axial motion of the shaft.

RE: Stress analysis on shaft -- deformation error

If he adds axial constraint at the end, he will need to split the face and get a single point/node to constrain so as not to induce unwanted stiffness and bending stresses.  

TOP
CSWP, BSSE
www.engtran.com  www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."

RE: Stress analysis on shaft -- deformation error

Yes, possibly.  Could add an axial restraint at one of the snap ring faces too, since that's where it would happen in real life.

RE: Stress analysis on shaft -- deformation error

Quote:

applied constraints in the snap ring grooves because specifying the bearing locations proved difficult

Sounds like you need to split faces in SWx or Pro/E.
Attach the original prt here and your sldprt here with loads and constraints as you applied them and I'll take a look.
You should get roughly equivalent results in both programs on this anaylis.

RE: Stress analysis on shaft -- deformation error

Oh, just realized.

You have no restraint against rotation about the shaft axis?  That's a no-no for a static FEA solver.

RE: Stress analysis on shaft -- deformation error

There is an echo in here.

Quote (kellnerp):

He cross posted to eng-tips. The answer is here.

To remove rotation, setup an axis along the axis of the shaft and prescribe a tangential constraint.
The rest of the discussion of this problem is here.  

TOP
CSWP, BSSE
www.engtran.com  www.niswug.org
www.linkedin.com/in/engineeringtransport
Phenom IIx6 1100T = 8GB = FX1400 = XP64SP2 = SW2009SP3
"Node news is good news."

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