L.A.B. said:40 Nm or 4 Nm, the tab washer would prevent the nut from loosening....wouldn't it?
A thread fixation needs a certain tightening torque which is specified by the designer in order to fulfill what he intended. So IMHO a 4Nm tightening torque is already loose. A tab washer prevents the nut from rotating but not really from loosening.
Do you have any actual evidence the nut will come loose unless tightened to the listed torque figure?
Do you honestly question this? Sorry, but that's rather pointless. There is a sh*tload of evidence for this fact probably back from the days when threads were invented. A nut with insufficient pre-load will come loose. A tab washer is a loss-prevention device and not intended to maintain clamping forces. A threaded fixation loses a lot of clamping force by very, very little rotation, less than the inevitable backslash of a tab washer. If you don't believe me just go the next place were they teach mechanical engineering.
Apparently, a locknut (counter nut) according to you, would be a suitable 'engineering' solution, yet a tab washer is not?
Do you understand the fundamental difference between a locknut and a tab washer regarding the contact forces at the thread and at the contact faces between the adjacent parts and what that means for maintaing a proper pre-load? If you do then the question is rather odd. If you don't then the answer is simply yes.
Tim