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Aluminum or Nylon & Mechanics of a spacer.

  1. Jan 18, 2010 #1
    Moderator's note: thread moved from Homework Help forums to Mechanical Engineering forum. Welcome to PF an1mal_69 :smile:

    Apologies, this is not homework, but a real world problem.

    1. The problem statement, all variables and given/known data
    Front suspension system, consisting of 2 wishbones supporting a wheel hub via (x2) ball joints at the top and bottom. Other connections are apparent, for steering etc, but not relevant in this instance. The ball joints are secured to the arms with 4 bolts.

    The proposal is to template the top ball joint and insert a spacer of around 30mm between the arm and ball joint using extended and uprated fasteners.

    I had intended to make the spacer from Acetal Nylon having compressional properties equal to or greater than Aluminum. Certain individuals have questioned the material citing the spacer will be subject to shear stress, I argued the fasteners would be taking the shear loads.?


    balljointmock.jpg


    If you take the rough diagram into consideration..assume the bottom plate as fixed, and there are (x4) fasteners clamping the spacer in place. If a force is applied to the bar on the upper plate (in any direction) what are the effects/loads on the spacer.?

    Many thanks in advance, Nik..
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
    Last edited by a moderator: Jan 18, 2010
  2. jcsd
  3. Jan 18, 2010 #2

    Mech_Engineer

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    Ideally, shear forces should be absorbed by friction in the joint and the fasteners should only see tension due to their initial preload. If the joint slides (thus applying shear to the fasteners) it could be considered a joint failure.

    Unfortunately, the coefficient of friction between nylon and aluminum is probably pretty low, especially when compared to bare aluminum on aluminum (which is around 1.0-1.1 I think). This means if you use a nylon spacer, you will need to apply more preload on the bolts to prevent a joint failure (shear sliding).
     
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