Let me preferance this by saying...I don't claim to have "THE ANSWER" but some general thoughts on this subject:
Was the torque wrench properly calibrated and set to zero after each use?
Remember a torque wrench can and at times be used incorrectly.
- Yep a LOT of professional crews have rookie guys that don't know how to use a torque wrench on thier crews
I have never seen torque sticks used in the pits. An over torqued condition can "fitique" the threads.
- Who said anything about torque sticks ???
I did some research for a Nascar team using a Skidmoore. A Skidmoore is device which can measure clamping force. My research showed that a clean and lubicated stud and nut can increase clamping force by 80 percent. The natural oil from your skin can increase clamping force by 20 percent verses and non-lubricated stud.
- It is the SHEAR force that is more important in this situation, see Randys post about the fence boards. As I understand it, it is the shear force (a huge amount) that caused the failure not the pulling force (very little if any)
Fastener and Screw / Bolt Design, Formula and Calculation* -* Engineers Edge