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Operating a spring in both tension and compression

  1. Apr 13, 2010 #1
    Most of my physics homework problems have had no problem treating a spring as being able to operate in both compression and tension. However, I now need to find a way to actually implement that for a design project. The general idea is a test bed creating opposing force to test a new actuator. I'd like to put a spring in between the two force creation mechanisms to transfer both compressive and tensile forces, as well as allowing for some slippage in their operation.

    Looking at most spring manufacturer's catalogs show a distinct separation between compression and tension springs. Some initial research shows that it wouldn't be advisable to try and weld a standard coil spring due to their high carbon content. I'm currently looking at leaf springs as a possible method since the way they're attached to a car easily allows for transmission of both compressive and tensile forces, but I can't find anywhere if they're actually meant to operate under both conditions. Are they? If not, what spring setup is actually able to operate in both compression and tension?

    tl;dr: How to actually use a spring in both compression and tension?
     
  2. jcsd
  3. Apr 13, 2010 #2

    berkeman

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    Welcome to the PF. I'm an EE, not an ME, so I'm of limited help. I do have to ask the obvous question, though, can you just use two coaxial springs for your setup? A tension spring inside a compression spring, with appropriate mechanical connections made to both at each end?

    I think tension springs would usually have U-bends at the ends for making mechanical attachment, like the springs in drum brakes, as shown at this other post:

    https://www.physicsforums.com/showthread.php?t=394960

    And compression springs would usually have flat ends, for the same reason. Maybe the main difference between compression and tension springs, is just how they are mechanically finished at the ends, based on how they are used mechanically? (I could be wrong of course)
     
  4. Apr 13, 2010 #3

    Q_Goest

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    Fundamentally, there's no reason a spring can't be put into tension and also compression (not at the same time of course). :wink:
     
  5. Apr 14, 2010 #4
    For clarification, this is something along the lines of what I had in mind:

    Yes, the only real difference between compression and tension is the finish at the ends. However, that's the problem.

    With the coaxial setup, when the system is at rest, the tension spring is at minimum length and the compression spring is at max length. Compressing the two further would cause the tension spring to buckle (Not so good). Extending them further would cause the compression spring to extend (Which is fine), but my problem is that I don't know how to mount the compression spring to transmit a tension force to it.

    "In theory, there's no difference between theory and practice. In practice, there is."
    That said, what kind of spring and how would you mount it?

    The standard mount for a vehicle's leaf spring looks like it would work for transmitting compression and tension, but are leaf springs meant to be extended as well as compressed?
    250px-Leafs1.jpg
     
    Last edited by a moderator: Apr 17, 2017
  6. Apr 14, 2010 #5

    berkeman

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    If your coupling mechanism is selctive, then each spring could function as designed...
     
  7. Apr 14, 2010 #6
    The test bed is meant to be operating at forces of up to 250 kN. At that range, I'd rather have a statically connected spring than trying to change out/reconnect springs in the middle of a test.
     
  8. Apr 14, 2010 #7

    berkeman

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    I didn't suggest that you have to change out springs during the test. Make it one assembly.
     
  9. Apr 14, 2010 #8

    Q_Goest

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    How about a conventional, closed and ground helical spring? Put U-bolt clamps around the ends to hold it to something like a flat plate.
     
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