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Simple analysis help

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Message 1 of 6
buckeye81
456 Views, 5 Replies

Simple analysis help

I trying to do a simple analysis of a large steel cylinder resting on an aluminum frame.  The can is free to slide on the frame, all weldments are bonded.  The analysis runs and show a stress range from 0 to 28 ksi but the entire frame is colored blue, i.e. 0 ksi.  There should clearly be some high stress areas where the frame bends and around the welds.  What might be the cause for just seeing a uniform stress state?  The deflections show so that's not an issue.

5 REPLIES 5
Message 2 of 6
buckeye81
in reply to: buckeye81

Here is a picture of the von Mises stresses

 

Message 3 of 6
AstroJohnPE
in reply to: buckeye81

Hi Buckeye81,

 

Based on what I see, it looks as if the cylinder is not restrained. You should check that it is making contact with the rollers. You may need to put a small "flat" section on the rollers and cylinder so that you have contact over an area instead of a line (or point depending on the profile of the rollers).

 

It has been a few years since I used Inventor's stress analysis (I presume that is what you are using, right?), but chances are the stresses are being shown properly based on the analysis setup (garbage in -> garbage out). If you display where the maximum stress occurs, it is probably at a single point, and the rest of the model has low enough stress that it appears blue (somewhere between 0 and a couple ksi).

 

When you write that the displacements show, you're implying that they are correct. Are they? The stresses are shown, too, but they are not correct. Smiley Wink 

Message 4 of 6
buckeye81
in reply to: AstroJohnPE

Actually the cylinder is restrained and is tangent to the rollers.  I have since modifed the model to remove the cylinder, create flats at the proper angle on the rollers, and apply the equivalent load on those flats.  Same result.  Doesn't matter if I modify the scale of the color bars, the structure remains entirely blue...constant stress everywhere.

Message 5 of 6
zhuangs
in reply to: buckeye81

To check this, can you pick a node in the conact area and then check the results of that node, to see whether the result is still zero.

 

Next, activate the gravity option, and then run the analysis.  After that, check whether the model is blue for stress result.

 

-Shoubing

Message 6 of 6
AstroJohnPE
in reply to: buckeye81

buckeye81,

 

You may ultimately need to post your problem to the Inventor discussion group instead of this one (Simulation Mechanical is separate from Inventor), but here are a few other thoughts that may help determine what's going on.

 

  1. One of the option in the "Display" group is to display the "Maximum Value". If you turn that on, it puts a probe on the model at the location of the maximum stress. There should be some red there.
  2. What version of the software are you using?
  3. I presume your description of the cylinder being "tangent to the rollers" indicates that in the assembly, you added a "Constraint" of "Tangent" between the two parts. (Other options are "Mate", "Angle", and so on.) I have not used Inventor 2014 (that's the version I have) for stress analysis, but it appears that the assembly constraints are not related to the "Contacts > Manual" that you can define in the Stress Analysis environment. It's the "Contacts" in the stress analysis where you would indicate that the cylinder is in contact with the rollers ("Separation" to use the Inventor terminology). By default, all of the parts of the assembly are bonded together (welded, glued, all melted together, however you want to think of it). But I do not know if Inventor detects point-to-point contact, line contact, or surface contact in order to bond parts together.
  4. What are the displacement results in your analysis?

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