MES bolt pre-loads not activating correctly?

[Anonymous]

Hello all, I am trying to simulate something in MES with bolt pre-loads and I am led to believe that they are not working correctly. For starter's, there is essentially no initial stress in the joint despite my 1/2" bolt having around 120 ft-lbs applied to it. There is evidence that some type of a preload is there...i get stress contours at extremely low levels that show something is happening around the connection, but it is not magnitutidenly (word?) accurate. I applied 1440 lb-in of torque to the connection and at timestep=1 (.05s) i am seeing an element axial force of approximately one pound. I removed all other loads to make sure something funny wasnt happening where the pre-load was being overcome and am seeing the same result. Any suggestions or has anyone else had this error? it is a little frustrating.

 Sim Mech 2015

Thanks,

[John_Holtz]

Hi Dylan,

What Torque coefficient (K) are you using for the bolt preload?

What about the displacement? Are the parts moving closer together? The reason that I ask is because the preload needs to be resisted by creating a force in the parts being bolted.

• If two parts are being bolted together but there is no contact between the parts, they would displace (move) through each other but create 0 stress.
• Similarly, if you are using surface-to-surface contact between the parts but the contact stiffness is to low, then the preload goes into compressing the contact but doesn't generate much force. (Or if the parts penetrate each other, contact may be disabled because the solution assumes that the penetration is a violation of the analysis.)
• Or if you are bolting two sponges together, they can be compressed but not generate any significant force because they do not have much stiffness.

To summarize, the bolt starts with a load at time 0 but the parts have no load at time 0. So the bolt compresses the parts which generates a load (or displacement) in the parts but reduces the load in the bolt.

The above items are just guesses. If you still have questions, feel free to post some images that show what is happening in the analysis, or better yet, attach an archive of your model. (See "Create, Post, or Provide an Archive of your model").

[Anonymous]

Thanks John for the speedy reply, all of your suggestions make sense and I am looking into them. Another thing i thought of over lunch...i had to make my own materials in Inventor and then i Imported them into Sim Mech when the model came over. The model ran fine in a static analysis (pre loads and all), Could this play any roll in the behavior I am seeing? I'm not sure if MES looks at a material property that I would not be able to enter in Inventor, although this would lead me to believe the analysis would fail and I would receive an error. 

Thank you

[Anonymous]

I have no idea what I fixed but it seems to be working now. The only thing i changed when i rebuilt the model was i defined my preload axially as opposed to with a torque and a coefficient.