[PSUBS-MAILIST] calculation

[Sean T. Stevenson via Personal_Submersibles]

Hank - the force developed is dependent on the stiffness of both the bolt material and of the specimen you're pushing on.  You can't necessarily equate this directly to torque because of friction in the bolt threads and at the bolt end contact, and of course the elasticity of the bolt itself. You can only estimate it.  There are many online tools for calculating the developed tensile force in a bolted connection, for example, but these consider only the bolt as the deformable element, and require an accurate estimate of coefficients of friction, and this will change with lubrication. As you complicate the system, it becomes more geometry dependent.

A 1" - 8 UNC 2A thread is 8 threads per inch, so a set number of turns will give you the approximate axial displacement (0.125" per revolution - approximate because the bolt will change length under load). If you assume a rigid fixture, then your strain is equal to the overall change in length (calculated from # of bolt turns), divided by the gauge length (distance over which the length change occurs, which would be the length of your specimen measured between the rigid fixture and the end of your jack bolt). Compressive or tensile load is then calculated based on the modulus of elasticity of the specimen.  Alternatively, you can measure the load (make the bolt or fixture into a load cell or strain gauge the specimen) and calculate the material properties.

Load, axial displacement, modulus. You need any two to calculate the third.

What are you making / testing?

Sean


On July 6, 2015 6:26:49 AM MDT, hank pronk via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>Hi all,
>I need help, can anyone tell me how to calculate how much force a bolt
>can push or pull using a torque wrench to turn the bolt. So how many
>foot pounds of torque does it take to rotate a bolt to  create 250 lbs
>push with a 1 in coarse thread bolt.  I need to make a test fixture.
>Hank
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