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346gnu13-Aquamarine
13-Aquamarine
March 19, 2014
Question

Fasteners

  • March 19, 2014
  • 3 replies
  • 6882 views

Hi,

Why are we allowed to create a preloaded fastener that has neither fix separation OR a contact region? (image1)

The fastener is 'shrunk' (image3) but unsuprisingly, the forces are all zero when the model is run. (image2)

I have only tried this in Creo2.0 M060.

Thanks


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    3 replies

    3
    346gnu13-AquamarineAuthor
    13-Aquamarine
    March 19, 2014

    Steven,

    Thanks for the attachment,

    every time I ask TS about fasteners they send me this or similar ...

    3
    346gnu13-AquamarineAuthor
    13-Aquamarine
    March 19, 2014

    Steven,

    I discovered I didn't have to have either a contact or use fix separation.

    I just get the warning that surfaces won't be bonded and it lets me do it.

    I would have expected an error forcing me to do one or the other or a warning stating that fix separation will be switched back on because I don't have a contact.

    Under what circumstances would it be useful to have neither?

    Thanks

    D
    danderson1-Visitor
    1-Visitor
    March 19, 2014

    Steven,

    It was my understanding that with Creo 2 you no longer need to run it a second time as stated in your pdf as PTC has made changes to how fasteners are handled with the Creo 2. There is still the issue that a Simulate fastener going thru 3 or more parts is not supported by any version of pro/e (this is what PTC's top level tech support is saying) even though it seems to work. I see Charles setup involves 3 parts being fastened together.

    Don Anderson

    M
    mfischer18-Opal
    18-Opal
    March 19, 2014

    Hi Steven,

    You are correct. In Creo 2.0, you still need to run it twice.

    The background....when a fastener preload is specified, that amount of load is applied through the 'fastener-spring' to the un-deformed model. As the model deforms, the resulting (actual) preload is typically less than the value specified and is reported in terms of a measure. Based on this information, the user has to estimate a new value for preload that will result in an actual preload equal to the desired value and rerun the analysis. Typically they would have to scale up the preload value and then rerun the analysis.

    In Creo 3.0, there is a new option that will allow the system to run the initial analysis, determine the value, automatically scale the preload and re-run the simulation. The result would be that the specified preload force would be what is applied to the deformed object.

    Hope this helps.

    Mark

    M
    mfischer18-Opal
    18-Opal
    March 19, 2014

    This is a good question......

    When placing fasteners with preload, you really have two options....or you will get the results you encountered, which in most cases is not desirable.

    The decision you have to make is accuracy or speed....

    1) Fix Separation

    • When placing a fastener with preload force, you should first select Fix Separation. This will utilize a linearized contact interface between the two surfaces. Fix Separation works fine as long as there is a good amount (say 90%) of the compression at the interface. Setting the ‘Fix Separation’ ON. If there are warnings in the RPT file (saying that the Fix Separation is not working as expected), then use the real contact interface.

    2) Real contact interface

    • If you are using a contact interface with friction between the two objects (surface or component), then you would turn off fix separation. This type of analysis is more accurate but will force nonlinear analysis and will take more time to process.

    In your example, when you turned off fix separation, the system did not provide a warning, it just stated that the two highlighted surfaces will be a contact surface pair. Now you would need to create how these surfaces should interact. By default they are free...unless you created a contact interface between them. This will provide the proper results you are looking for.

    Does that make sense?

    Thanks,

    Mark


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