Learning Forum

[RoyalFlowers]

Hi everyone,

I am going to use the Bolt-Thread Option of Contact Geometry Corection for a simple block-screw model. A I know in this modeling we simulate screws as simple cylinders, then screw information (i.e, Pitch Distance, Pitch Diameter, Thraed Angulation)  is applied in contact geometry correction. In this case, should we model cylinder with Major Screw Diameter or with Mean Screw Diameter?  Moreoevr, I would like to know what is the backgraound theory beshind the Bolt Thread. Does it work in this way that we define screws as simple cyilnders which have frictional contacts woth holes and by importing pitch ditacne, picht diameter, and thread angle, the helical path of thread is determined and nodes of cylinder and hole located on this patch are bonded or tied to gether. If this assumption is correct, then in the initail geometry the screws should be modeled as simple cylinders with mean screw diameter not major screw diameter. I am grateful if you could advice me in this regard too.

I appreciate your kind answers in advance.

Best regards, Shabnam Samsami 

[Sai Deogekar]

Hello Shabnam,

The user-specified thread geometry data is used to calculate the contact normal between the bolt threads and the nut threads. The actual geometry of the bolt and nut is not altered in any way.

You can refer to the section about "Simplified Bolt Thread Modeling" from ansys help:

https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v201/en/ans_ctec/ctecgeomcor.html

If you look at the first point under "Keep the following points in mind ..." it states "In general, the solid model is based on the major diameter d, which is the diameter of the non-threaded surface."

So even when using geometry correction, you would model the bolts using their major diameter.

 

Hope this helps,

Sai

[RoyalFlowers]

Dear Sai,

Thanks a million for your illuminating answer. 

As I understatood, when we model bolt and nut as major diameter of screw, then using Bolt-Thread option provides virtual modeling of threads along the bolt axis in the direction defined by the thread angle as well as to in the direction preipendicular to contact surface to the depth which is equal to the difference between major and mean screw diameters. In this way, on the contact surface, the nods locate on the helical path of threads are contrained by bonded contact and for in-between space frictional contact method is applied. 

I am grateful for your kind answer in advance.

Best regards, Shabnam Samsami