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  • Fasteners matching strength -washer

    Discussion in 'The main mechanical design forum' started by KevinC, Sep 5, 2014.

    1. KevinC

      KevinC Well-Known Member

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      Hey guys,

      Need some help here. Can someone share some of their experience in using harden (steel) washer? As the old saying goes: "A chain is as strong as it's weakest link".

      I'm designing some bolting application here, and I put in a 75% of the proof load as my pre-load. Of course I know I'll match grade of bolts and nuts (let's say Grade 5- 120ksi is in used, 85ksi proof), the store that I go to keep suggesting me using 90-95ksi tensile strength washers (around). Am I good to go with it? The idea that I get is: since I only bolt to 75% of proof strength and since washer is only undergo compression and only in compression yield, but not exceed the Ultimate Tensile strength rating yet, so it is still safe. Is it so? If the loading doesn't change much, temperature doesn't change much, and environment is not corrosive, any concern I should have? What about material creep?


      Of course the best answer is to use a washer having tensile strength >grade 5, that is a given, but not the answer I'm interested.

      Please DO NOT suggest ways of designing the application, please only focus on washers and relating issues only, I do not want to go off tangent to nowhere.
       
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    3. Dana

      Dana Well-Known Member

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      Look at the actual compressive stress in the washer and determine whether you need more strength than the basic washer.

      In general, hardened washers are not needed unless you need to spread the load over a softer material, or to spread the load over a larger clearance hole.
       
    4. KevinC

      KevinC Well-Known Member

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      It make sense to evaulate stress on the washer, any knowledge of bolt tension loss due to creep overtime?
       

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