# Modelling a joint in a threaded rod, joint, nut and washer assembly

1. Sep 6, 2014

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I am trying to use computer modelling to see stress. I want to compare it to my hand calculation, which uses the frusta cone method to find the stiffness of the joint. This way, I can check my calculation in a conceptual way.

The model includes a nylon insert nut, a threaded rod, a washer and a joint (some people refer to the joint as a member).
I wanted to model these parts as solid for realism.
The member is made of three plates. Only the plate furthest from the washer is threaded.

The results that I get using ANSYS 14.5 are garbage and I cannot understand why (see the attachments for the model, boundary conditions and results). All contacts are set to 'bonded'. There should be a cone of stress, less at the top member, more to the middle, less at the bottom member. Please help.

Here is the model (630 kB):
https://www.dropbox.com/s/50od9jnfx507s8u/model.zip?dl=0
or use:
http://www.filedropper.com/model_3 [Broken]

Will a threaded rod / washer / nylon insert nut / threaded member actually produce a clamping force? Its hard to picture that in my mind.

Does the following equation apply to this situation:

F = 0.75 * Sp

Where F is the preload tension, resulting from the nut being tightened on the threaded rod.
Where Sp is the proof strength of the stud.

T = KDF

Where T is the Torque required to produce the force that clamps the assembly together
Where K is the nut factor
Where F is defined as before.

Thanks.

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Last edited by a moderator: May 6, 2017
2. Sep 10, 2014