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    Discussion in 'Calculations' started by Bouty3153, Jun 14, 2013.

    1. Bouty3153

      Bouty3153 New Member

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      To start, I am not an engineer. However my company has put me on a project that requires knowledge above mine. I have worked on many design projects but none where the physical characteristics of the parts have been so crucial to the success or failure of the design.

      I will attempt to explain the project, but there is an attachment of what I have came up with so far.

      It is a clamping style fixture that needs to be secured around a 1" rod while 10,000lbf will be applied to the ears in a vertical pull. The plates are 1" thick with 1" Socket head bolts to pull the 2 plates together.

      Ideally, the plates will be bolted together with enough force from the 1" bolts to basically crimp around the rod and hold it secure while cables are hooked to shackles in each hole on the end. It will be used to tension cables that will be pulled at 10000lbf.

      My questions are:
      1. Will the 1"-13 UNC Bolts apply enough pressure to secure the clamp to the rod and allow no slipping when the force is applied.
      2. If the amount of torque needed to actually "crimp" the plates can be reached with the 1" bolts, will the socket head type bolts be the best route? Or would regular hex head bolts be more sufficient in reaching the amount of torque needed?

      Thanks ahead for any response at all... <a href="http://s278.photobucket.com/user/Bounty3153/media/RodClamp.jpg.html" target="_blank"><img src="http://i278.photobucket.com/albums/kk84/Bounty3153/RodClamp.jpg" border="0" alt=" photo RodClamp.jpg"/></a>
       
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    3. suryanshastri

      suryanshastri Member

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      problem

      Photo is deleted & please convert this units to MKS system.
       
    4. KevinK

      KevinK New Member

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      I hope it's not too late for this response to be helpful.

      Firstly, you'll need to know the material of the 2 plates and the rod in order to determine the coefficient of static friction between them. For example, if both were made of a mild carbon steel, the coefficient would be somewhere around 0.8. Reference this link for general values for a variety of materials: http://www.engineeringtoolbox.com/friction-coefficients-d_778.html. In this case, a larger coefficient is desirable. One way to achieve this is to use a rougher surface finish on the rod and plates, if possible.

      From there, the equation for static friction force (F) is simply: F = mu*N, where mu is the coefficient of static friction, and N is the compressive load holding the two plates together. You can rearrange that to get N = F/mu, which tells you the necessary force holding the two plates together in order to hold your load of 10000lbf without slipping. If we assume mu = 0.8, and assume the 10000lbf load is evenly distributed between both plates (so 5000lbf applied to each plate), that gives N = 6250lbf. Because there are two bolts holding the plates together, each bolt would then have to apply 3125lbf of compressive load to the plates. Assuming the bolts are strong enough to withstand this load (see below), then they will be able to supply it, but it may be difficult to produce enough torque to tighten the bolts enough to reach the desired load (some experimentation would probably be required here). If necessary, more bolts could be added to the assembly to reduce the load requirement of each individual bolt.

      Now, that said, all of the above is purely theoretical. With loads that large, there will be some effects of local deformation of the rod and plates that are difficult to account for in calculations. Hence, a rather large safety factor would be recommended. i.e. Design the bolts to supply 1.5 or 2 times as much compressive load as your calculations call for. You'll have to look at several aspects of the bolts to determine what size is needed to withstand that load, including tensile strength and pullout strength (i.e. how large a load is needed to strip the thread). After a cursory search, ASTM A325 may be a good place to start: https://en.wikipedia.org/wiki/ASTM_A325.
       

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