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Proof Load

  1. Aug 7, 2008 #1

    What is Proof load of a bolt?
    I need to calculate the proof load of a bolt?

    I have searched the net but could not find it.
    Please help me.


  2. jcsd
  3. Aug 8, 2008 #2


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    The proof load is just the load that the bolt is tested to. It is above the normal working load of the bolt and is used to verify or "proof" the design.

  4. Aug 12, 2008 #3


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    Proof load is the load slightly below yield strength of the bolt and well below the ultimate strength. You don't calculate it, you measure it. Tensile testing is the only way to do it accurately.
  5. Aug 12, 2008 #4


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    araanandv2: On average, bolt proof strength is Sp = 0.90*Sty, where Sty = bolt tensile yield strength. Nonetheless, bolt proof strength is published for each bolt property class, which is more accurate than approximating it, and is easy to find on the net.
  6. Aug 13, 2008 #5


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    Oops. I meant to say, ...and is easy to find on the net if your bolt is carbon steel (not stainless steel), and your bolt head is marked with a common bolt property class, such as 5.8, 8.8, or 10.9.
  7. Sep 6, 2011 #6
    Proof load is used instead of yield strength because of the stress concentration that occur at edges and corners, and in particular at the threading. The stress concentration results in local yielding before the yield strength is exceeded, so the material will yield very close to the thread though the rest of the material is still intact.
  8. Dec 12, 2011 #7
    What's the proof load for AN bolts and NAS1351 screws?
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