I have experience with using torque to yield bolts in design. Why do people use torque to yield bolts with torque+angle instead of just specifying a torque value? This is because they are trying to achieve a consistent CLAMP LOAD in the joint. If you just use torque, your resulting clamp load will vary quite a bit because many, many factors affect the torque application (thread quality, lubrication on threads, etc.). If you look at the torque vs. angle plot of a generic bolt, the torque increases to the yield point and the torque value flattens out for quite a bit more angle application until you reach the failure point. Audi also ensures that the bolt is placed in yield because bolts relax. If you are past the yield point in the torque vs. angle curve then some relaxation in the bolt maintains the clamp load because the torque vs. angle plot is mostly flat past the yield point. Lets say your threads are dry and munged up, you may put 30 N-m on it but not reach the yield point, any relaxation then results in a loss of clamp load. Not ideal. Its also possible that since the bolt is stretched, your new yield torque is 25 N-m. So you keep adding angle trying to reach 35 N-m but the bolt breaks at 25.
I say all of this to say you CAN re-use torque to yield bolts but you are introducing even more variables into that resulting joint clamp force. At least use loctite to help combat the bolt relaxation a bit so you don't lose joint clamping force. And if you find yourself turning and turning the bolt, trying to reach X N-m, STOP!
I'm not disparaging anyone that chooses to re-use bolts or the companies that recommend that course. It can surely be done and chances are you'll be perfectly fine. I just choose not to go that route.
Engineering nerd rant over.
Reply With Quote
CPO
TBD:Akebono pads/Slotted Rotors or JHM 382mm Kit
Originally Posted by Rbb1485
Bookmarks