Flange bolt connection FEA

[Anonymous]

Hello Experts,

I am doing a study on bolt connections (M24 8.8) (Preload Fv = 160300N) for our Gearbox flange

Approach 1:

Mesh element size: 50 mm

 Contact type: Separate/Not sliding

                          Friction coefficient: 0

                          Max activation distance: 51

Load definitions: I have added all our operational load and mass of other component then defined as a single load (327238N).

Result: Reaction force at the bolt (Beam End A-X):  456 kN   

Approach_1Approach_1

Approach 2:    

Mesh element size: 50 mm

 Contact type: Separate/Not sliding

                          Friction coefficient: 0

                          Max activation distance: 51

       Load: I have defined the operational load as a 'moment' at our output shaft and also mass of the other components (shafts, motor, etc…) as 'force' at respective positions.

Result: Reaction force at the bolt (Beam End A-X):  171 kN   

Approach_2

Here is my problem In my both approach I am getting the same SPC force and moment, which means my load definitions in both approach were correct.

1) Why I am getting different beam reaction force between these two approaches, when the SPC force and moment were same. 

2) And also at some of the bolts I am getting beam reaction force lower than bolt preload (Fv = 160300N).

If anyone experienced this please share your comments.

Thanks in advance.

Karthik

[John_Holtz]

Hi Karthik,

An increase in the bolt load from 160 kN to 456 kN is a very large increase. Are the flanges separating? This is the only way that I can think of that would cause the bolts to be taking such a large load. Is there something else wrong in Approach 1? (Be sure to check the post Software problem with bolt preload in version 12.1 for a known issue with the bolt preload. Since your reaction forces are correct, I think this issue is not affecting your analysis, but it is something to keep in mind.)

If I understand the images correctly, all of the external loads are passing through the bolts in Approach 1, but only a portion of the loads are passing through the bolts in Approach 2. This could explain why the load in the bolts is different.

The bolt results in Approach 2 make more sense to me. The purpose of preloading the bolt is so that the members take most of the load by releasing some of their compression. The loads in the bolts should only increase a fraction of the total load.

[Anonymous]

Dear Mr. John,

Thank you so much for your reply......

Are the flanges separating?   Yes.

 Today I have experienced a another problem as follows.

As I mentioned above I have used the approach 1 but with M48 bolt size instead of M24 bolts

Problem:

Beam reaction force with M24 is 456KN, so without bolt M24 preload(160kN) is 296KN. (which is match the theoritical clculation)

Beam reaction force with M48 is 740 kN, so without bolt M48 preload(679,6kN) is 60KN. (which is not match the theoritical clculation). 

My question is why the beam reactions force for M48 is to low. 

I looking forward for your comment on this issue.

Thanks in advance,

Karthik

[John_Holtz · Accepted solution]

Hi

My guess is that the flanges are separating with the M24 bolts, and therefore the bolts are taking the entire load. But with the M48 bolts, the flanges are not separating. Therefore a small portion of the load is taken by the bolts (increasing the tension), and the rest of the load is taken by the parts being bolted together (decreasing the compression).

In other words, the bolt is only one "spring" in the system. The bolted components are another "spring" that act in parallel with the bolt. Based on the stiffness of the bolt and components, the live load generally increases the bolt tension by a small amount and decreases the compression in the components by a large amount. This continues until the components separate at which time the bolts begin to carry the entire load.

Otherwise, you need to provide some hand calculations and a model that shows what is right or wrong.