Bolt Hole Cracking Problem - excessive bolt torque?

[Vladman]

I have a bearing bore with 6 holes around it to hold a bearing cap. Several holes cracked, presumably due to overtorqueing. The bolts have spiralock threads.
Question: would excessive torque cause the fractures, or would it strip the threads first. The holes are not through the part.

Also, are there any books that deal with various types of fractures in fastener assemblies?

Thank you

 

[TowerEngineer]

This is a difficult question to answer without knowing the orientation of the cracks in relation to the load. Can you provide a more detailed desciption of the crack orientation and the load direction?

They simply could be due to excessive load on the bearing which load is also resisted by the bolts and the material in which they are located. Is there any evidence of elongation in the diameter of the holes? What orientation do the cracks have in relation to the hole elongation, if any?

 

[Gourile]

Hi!
This kind of cracking may have two reasons:
1) Material problem. Check the certificate of the material or make proper tests on it to see if the characteristics are correct.
2)Are the holes made by Punching? It is well known that Punching makes microscopic cracking around the hole which will propagate over the time, especially when dealing with cyclic loading. Drilling wouldn't cause this problem. Normally, if the hole dia is grater than 12mm, a preliminary punch hole is made with a 5mm dia less than desired and then it will drilled through to reach the desired dia.

Afterall, you should look for the technique for making holes as the reason. I don't think that overtorquing might cause cracking.
Have lock.

 

[diamondjim]

I do not know if you are just curious or
want to repair what you have. If you are
trying to repair, you might consider
keenserts if you have the room to drill
larger holes and tap them for the keenserts