Bolt torque discussion

krazykuda said

We used to monitor torque vs angle when we torqued to yield... You stretch the bolt and monitor torque vs angle and when the curve bends over, you stop when the slope of the curve goes 10% past the peak... That is how you get maximum yield and minimal stretch...

That is how you keep from putting too much permanent stretch in a bolt and achieving maximum clamp load... Once you get into the permanent deformation range, you are not getting any more benefit for clamp load....

Click to expand...

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?