Originally Posted by Spartarus
Well, you presented a good fair number of pretty shaky assertions there. One could even0 call them... Extra shaky.
Jokes aside, there is a tremendous amount of misinformation in your posts.
First, yes, any bolt can be overtorqued enough to stretch it.
Second, torque settings alone are an incredibly inaccurate way to ensure correct fastener preload. That is a fact, we can argue the engineering details if you like.
Third, most impact wrenches are adjustable, but none of them, not even one, delivers consistent performance. This is by the nature of delivery. The short duration pulses transfer energy in a discontinuous fashion, the final clamp load is influenced heavily by the frictional coefficients of both the threads and the surface which bears the clamp loads. It is also affected by the spring coefficients of the joint material, the heat generated during tightening, and the motion of the gun. This can be demonstrably proven.
Fourth, even with a powerful impact gun, you are unlikely to even damage a lug, much less break it.
Fifth, all steel fasteners stretch when loads are applied. This is called elastic deformation, and it's what gives the bolted joint it's tensile load. For all intents and purposes, elastic deformation in steel can be repeated an infinite number of times without causing fatigue or failure. In other words, no, they can be "overtorqued" an infinite number of times without causing "cumulative damage."
If they are stretched beyond the yield point, they will undergo plastic deformation, which is irreversible and causes damage, usually visible. These are your "stretched lugs." That is "cumulative damage." But in order to do that to a normal, undamaged wheel stud, you have to have an extra bigass breaker bar or you need to join the avengers.
Did you know, for example that if you torque a fastener, then remove, clean, and lubricate it, and apply the same torque again, you will almost double the tensile load applied to that very same fastener? Yes, that $40 Sears click-wrench is a proper precision instrument, you know. *sigh* A $300 digital torque wrench is subject to the same problems and limitations.
For that matter, I have replaced hundreds of wheels with impact wrenches. Never lost one. Never had anybody else lose one.
Now what's really funny is watching people replace components with different and dissimilar ones, sometimes made of different materials than the factory components, and then faithfully copy the torque specs right out of the manual. Now that is UN-F*CKING-SAFE For reasons I can demonstrably prove over and over and over.
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