Using Mechanica Lite to analyze stress in a rotating shaft

[gkelson]

I'm having trouble running a Mechanica test on a shaft. The version of Pro/E I have only has Mechanica Lite. Here's a picture of the shaft. It's supported at the bearings shown and the rotor in the middle rotates. I want to study the stress in the shaft under the weight of itself and the rotor and under torsion from the rotor spinning.

http://i.imgur.com/iX2IK.jpg

I've opened Mechanica Lite from the shaft part file, but was unable to constrain properly where the bearings would be or apply the moment properly. The best thing I could think of was to add blocks as shown below that would act to support the shaft and that would essentially serve as the bearings. In the testing. I was able to constrain these blocks.

http://i.imgur.com/ci25b.jpg

Now I'm trying to apply a moment, but the moment option is greyed out no matter what I select (shown below). I'm also unsure how to apply gravity. I would appreciate help in running this analysis. My end goal is to see how much I can hollow out the shaft to save on weight and maintain strength. Thanks.

http://i.imgur.com/j13P7.jpg

 

[jvian]

I'm not sure how accurate the constraints will be with your bearing simulation but I think it is the best you can do. To apply a moment you need to create a point (i sketched one at the center of the front face of the shaft) and in the load definition box use the selected csys box option and re-select the world csys (or any other of your choice) and use the "total load at point" option and select the point you created earlier. This is standard moment definition in mechanica it just took a little work around to activate the option in Lite. Gravity is pretty straight forward, pick the world csys and apply the magnitude in the appropriate axis. In your model it looks like the x and z axes are perpendicular to your shaft. Just make sure what unit system your model is in and apply the right magnitude in the right direction. In your model I would choose the x-axis and apply -32.2 fps2 or -386.4 ips2 etc.

At a certain point I am pretty sure that the Lite will be very limited and your results may be inaccurate due to improper constraint definition and the lack of ability to handle stress singularities.

Hope any of that helps and good luck.

-J-

 

[kirrer]

Hi gkelson -

an alternative to Mechanica for this application is to look into the 1D shaft/bearing module of KISSsoft (

http://www.kisssoft.ch/).

You could build a shaft model and assign bearings at the specific locations, and get very quick results - including bearing lifetimes! Maybe it's overkill for your company in general to purchase it, but they do have a 30 day evaluation license which you could use to solve this problem & evaluate it for general use. Note, I am in no way affiliated with the company, I just loved using the software.

That having been said, I had a nice reply typed up until I realized that what I was recommending is only possible within Mechanica and not in Mechanica Lite (creating points with rigid links to the bearing blocks & allowing only translational DOF's to be fixed). If you have to use Mechanica Lite though, you may have better luck making the bearing blocks thinner so they don't impose as much of a rotation restriction on the shaft. Additionally, only one of the blocks should have all 3 DOF fixed; the rest should have only radial DOF's fixed.