Bolt torque discussion

nm9stheham said

Yep, I am pretty sure I understand all that KK; tnx. Did you mean 'maximum tension (stress) with minimal stretch' at the end of paragraph 2?

What I wanted to try to understand is the 'why' behind thinking that the longer head bolts needed to being torqued to a higher value, as Duane brought up. What is the objective of more torque with a longer head bolt? Are they trying to get to a more consistent stress/tension/clamping value? And are the looking at proportional stretch (strain) to judge the right value of torque, rather than just torque?

Click to expand...

The longer bolt for the most part doesn't need more torque than the rest of them as it would take a significant amount more length to make much difference... Yes bolt length can affect the torque on a bolt, but not as much as the thread diameter, pitch, size of the bolt (diameter), and grade of the bolt (hardness of the metal)... It would take much more amount of length to require the bolt to be torqued to a higher amount for the same diameter of bolt...

The clamp load on the bolt is what holds the joint together... The load on the bolt acts in the opposite direction of the clamp load... The clamp load holds the joint together until it sees a load/force higher than itself... Once the load on the bolt exceeds the clamp load, then the joint will separate and that's when the parts break... It's like push-pull... The clamp load is pushing the joint together, the force on the bolt is trying to pull it apart...