axially preloaded structural members


Results 1 to 2 of 2

Thread: axially preloaded structural members

  1. #1
    Member
    Join Date
    Nov 2018
    Posts
    17
    Downloads
    0
    Uploads
    0

    Default axially preloaded structural members

    Hello again all. so i was thinking of ways to decrease the deflection of structures for the various axis in a cnc machine other than just piling on more material and preloading came to mind, attached is a picture of my idea roughly and the test setup. the idea is to use a threaded rod and nuts on either end to apply a crushing pressure on the tubes long axis and hence preload the walls to increase its tension. now i did a basic test with what i had on hand last night but the results are not overly conclusive since the threaded rod i had was super soft and nasty so it stripped the threads and the tube section i have is not very wide in diameter so i dont think it would benefit much but as i was tightening the nut on the thread the dial was slowly creeping up so it looked like it was taking away some deflection.

    my main question is would this if applied on the right scale say a 1000mm long tube 300x300mm say 4mm wall thickness and a few internal braces using a 20mm or so high tensile rod to apply as much force along its length via thick end plates significantly decrease deflection in the tube? also any idea if this could be simulated in fusion 360
    also side effects of doing this, would it make the part slowly warp over time or some other effect i may not know about?

    Similar Threads:
    Attached Thumbnails Attached Thumbnails axially preloaded structural members-photo_2019-12-18_08-47-58-jpg   axially preloaded structural members-photo_2019-12-18_08-48-12-jpg  


  2. #2
    Member peteeng's Avatar
    Join Date
    Jul 2018
    Location
    dum dum
    Posts
    6254
    Downloads
    0
    Uploads
    0

    Default Re: axially preloaded structural members

    Hi Dingo - No, sorry does not change the global stiffness. May as well choose the correct size member to begin with. Light structures can be preloaded to gain stiffness but usually only in one direction eg a bridge against gravity, a bowsprit against a sail load. But on a machine that has to take load in multiple directions it's not a useful strategy. Yes, you can simulate this in FE systems not sure if you can do it in Fusion 360. I expect you can, just place the load on the ends and the service load at the tool...But beware of false results as F360 is a linear solver and if the structure is light and behaves in a non linear manner, which light preloaded structures can do then the result will be wrong and you can't tell if it's right or wrong. F360 solver is for stiff structures that behave linearly...Peter

    look up the rules of superposition and load sequencing linear vs non-linear



Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

axially preloaded structural members

axially preloaded structural members