Modelling a threaded rod, washer and nut.

[dirigible]

I am using ANSYS workbench 14.5 to model a threaded rod, a washer and a nut, which clamps together two plates. One of the plates is threaded. The threaded rod is threaded the whole length of the rod.
I want to simplify the analysis by not including the thread so I modeled the rod as a cylinder.
I sliced the threaded rod into pieces so that I can put bolt pretension on only one part of the threaded rod.
I cannot decide where to put the bolt pretension.
Can anyone suggest a method of how to calculate the effective length over which to apply the bolt pretension? Where should it go?
Is there a better way to simulate the tension that is caused by torquing the nut?
The point of the analysis is to help me find the stiffness of the bolt and the member and to see deflection in the system.

Thanks.

 

[dirigible]

The larger plate at the bottom of the picture is threaded but it is modeled as non threaded (see attachment)

 

[rb1957]

"how to calculate the effective length over which to apply the bolt pretension?" ... the length of the bolt that is being strained by preload ... so from the inner face of the head to the inner face of the nut.

i don't know ANSYS but i suspect that they have a bolt pretension tool. the olde way was to apply thermal loads, cooling the bolt elements so they shrank by the desired amount.

"Is there a better way to simulate the tension that is caused by torquing the nut?" ... you haven't suggested a way to apply preload so, no "better" way, but ...

"to simulate the tension that is caused by torquing the nut?", particularly given your intention " to ... find the stiffness of the bolt and the member and to see deflection in the system", then i'd suggest loading by "turn of the nut" control. each 360deg rotation of the nut forces the bolt to stretch 1 thread pitch, which sounds like an enforced displacement.

you know there's lots of material out there describing exactly what you wnat to measure ... so you can check your model against accepted practice.


another day in paradise, or is paradise one day closer ?

 

[dirigible]

Thanks for answering my questions rb1957.

"the length of the bolt that is being strained by preload ... so from the inner face of the head to the inner face of the nut."

My situation does not have a head because I am using a threaded rod and one nut and one washer. This is why I dont understand where to put the bolt pretension.
In reality, there are threads.
Would the part of the threaded rod that is being strained be the part that is connected to the internal thread of the joint?
Would the part of the threaded rod that is being strained be the part that is inside the portion of the joint that is not internally threaded?
Maybe a combination?

 

[rb1957]

is this a long threaded rod, anchored somewhere else ?

or short piece, basically a stud ? if stud, what stops the rod from rotating as you tighten it ?

another day in paradise, or is paradise one day closer ?

 

[dirigible]

The attachment shows the geometry. The threaded rod is about 30 mm long and 8mm major diameter. The rod is anchored by meshing with the thread in the lower plate and the thread in the nut.
The threaded rod is first twisted into the thread of the plate. Then the nut is twisted onto the threaded rod to create the bolt pretension.

 

[rb1957]

ok, the plate is really the nut, and th enut is really a "jam nut". i'd've thought that you were not generating a significant bolt tension between the nut and the jam nut. i think your bolt tension comes from what you're doing at this end of the rod and whatever is happening at the other end.



another day in paradise, or is paradise one day closer ?