Let me tell you how this file came about.
Some technician who did not know a damn thing happened to find a calculation formula in a book and typed it into Excel. He thought that once he had a formula, he could enter anything and the result would be universally valid.
Because he draws the parts himself, he specifies 0.1 every day.
The shop-floor workers also know that his company never performs acceptance inspections. Everyone is just trying to make a damn living; making money is what counts as being good. They make do and cannot be bothered to argue with him.
He thought he was so damn brilliant and excitedly put it out there to show off. What he did not realize was that if you actually tried to bend 4㎜ sheet metal to a bend radius of 0.1, whatever the sheet material, it would have cracked already. Where does any k-factor come into it?
All technicians have this bad habit: they always want to show off their skills. Look, I cannot resist showing off and explaining it myself: the radius must be at least half the sheet thickness. That is basic sheet-metal knowledge. Even if we are not specialists, we still know a little about stress.
This is hardly sharing knowledge; it is not much different from spreading poison.