Back in an earlier career dealing with fasteners, I believe it was the ASME that said applied stress could not exceed 1/3 of tensile strength or 2/3 of yield point.
I agree that 85% would be good, but how would it (or my 2/3) be determined in the field anyway.
Not sure where those ASME rules came from because they don’t match current recommendations. The tensile strength I can understand but it’s still a swag.
You can guess at it knowing the nut factor. If you know the tension spec and there are charts based on material, diameter, and a nut factor, you can calculate foot pounds needed. If you want to go past the basics...
Machinery’s Handbook gives the basic numbers, as does the Fastenal handbooks.
The thing is what we want is tension on the fastener..how much it is squeezing everything together. You can measure this accurately by measuring bolt stretch ultrasonically. A torque wrench really measures torque on the nut. 80% of the torque is friction in the threads. Only about 10-15% is actually tension...what we want. So it’s not the best way to do it but it’s the best we got. Using a thread lube, ANY thread lube, using the proper fastener, using a torque wrench...all contribute to getting very close to proper tension. Brass and copper alloys are naturally self lubricatjng, stainless and aluminum are definitely the opposite issue due tendency to easily gall. This gets us down to around +/-25% or better. Based on just mushing alpha spots there is a large window of acceptable tension which is why we don’t need precision tension but electrician “feel” fails more often than you would think. The required tension is pretty universal because really we only have a few conductor materials we work with (copper, aluminum).