Unrealistic stress distribution...

[Vesh]

I am trying to simulate a bolt surface pressing on the inner surface of a hole. The bolt is a bit smaller then the hole (M16 bolt in a dia. 18mm hole) so I created a volume region where the approximate contact of the bolt would touch the holes inner surface and got the result below.

View attachment 2627

I can see and understand why there is large stress at the edges of the surface region.

Is there a better way to simulate this?

Cheers...

 

[acook]

Hey Vesh,

It has been a long time since I perfromed a contact analysis in Mechanica, but I think I remember some of it. You cannot simply use a surface region becuase the contact area changes are non-linear w.r.t. to the load. See this tutorial for more information:
<a href="http://www.engin.brown.edu/courses/en174/Exercise/Exercis18.htm" target="_blank">
http://www.engin.brown.edu/courses/en174/Exercise/Exercis18. htm</a>

It is definately intended for either pre-Wildfire or Wildifire 1.0 as it uses the Menu Managers in Mechanica. So it will be a little different (in finding the commands) if you are using WF2 and later.

Hope this helps.

 

[Vesh]

OK, so thats what a contact analysis is.

Yes I absolutely agree wth you in ragards to the limitations of the surface region use.

I done a contact analysis and I think I got reasonable results. Took over an hour though due to the additional meshing around the contact region I presume.

Anyways, will work more with it... Thanks

 

[skraba]

One notice regarding design.


If this is not fit bolt, which obviously isn't (bolt M16 and hole fi18), shouldn't you be applying the stress through the prestressing of the bolt and not with shear forces?

 

[Vesh]

skraba,

Im not sure if I completely understand your statement.

But now I have the bolt in the analysis as well. The bracket is constraned, and only the bolt has an applied simulated load so its' surface contacts with the inner surface of the brackets' hole. (ie, I have applied a load to the bolt only, not the bracket this time)

I will post image when I get home. I presume this is what you are reffering to.

Thanks for the query.




Edited by: Vesh

 

[skraba]

My question wasn't really question but more notice. In our field of work bolts don'tcarry shear forces unless they are fit bolts, but they carry force or stress through the prestressing or pretensioning the bolt or in that case prestressing the flange surfaces so the form of the flange carries all the force or stress and not the bolt itself. Bolt is therefore stressed only with tensilestress and not with shear stress.