Proof Load

  1. Hi,

    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. stewartcs

    stewartcs 2,244
    Science Advisor

    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. FredGarvin

    FredGarvin 5,084
    Science Advisor

    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. nvn

    nvn 2,124
    Science Advisor
    Homework Helper

    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. nvn

    nvn 2,124
    Science Advisor
    Homework Helper

    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. 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. What's the proof load for AN bolts and NAS1351 screws?
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