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Thread: Bolt Torque v's Bolt Grade

  1. #1
    Associate Engineer
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    May 2014
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    Bolt Torque v's Bolt Grade

    I am trying to get my head around torque applied to a bolt, resulting clamping force (preload) and the grade of bolt used.
    Am I right in saying that the grade of bolt used has no impact on the effective clamping force induced by a given torque???

    The only factor to consider regarding the bolt grade is whether or not the resulting stress induced by the clamping force exceeds the bolt yield stress.

    My original thoughts were:
    - If I have an 8.8 grade bolt, torqued to X Nm, it would induce Y newtons of preload
    - If I use a 10.9 grade bolt, I would have to use a greater torque to induce the same Y newtons of preload as the bolt is "stronger"

    In researching this I am finding that my original thoughts seem to be wrong.

    Dalob

  2. #2
    Technical Fellow jboggs's Avatar
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    You are right. Your original thoughts were wrong. Clamping force created as a result of applied torque is determined purely by the geometry of the shapes involved (and to some extent, friction), which has nothing to do with the materials involved.

  3. #3
    Technical Fellow Kelly_Bramble's Avatar
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