Metal fatigue

Don Pablo · **on:** July 09, 2015, 11:59:19 PM

I bent the saw on my SAK slightly, recently.
While bending it back, I started thinking about metal fatigue.
So what I would like to know, is how much can you keep bending these sak tools before they get weak or break?
I notice that the saw metal is slightly different than the blade metal, to make it more flexible. So it probably won't get weak due to metal fatigue as easily?

enki_ck · **Reply #1 on:** July 10, 2015, 06:30:25 PM

Not sure, but you could do some testing for us.

As you've already bent your saw twice, you hav a head start.

AimlessWanderer · **Reply #2 on:** July 10, 2015, 07:37:20 PM

If you bend it past it's yield point, it will be a lot shorter lived than if you keep it within it's elastic limits. Fatigue starts off as a tiny hairline crack, that gradually spreads through the steel until the bit that's left isn't strong enough. The more stress you put the steel under, the more this will be exacerbated. Under normal usage, a SAK will handle what's thrown at it for generations, time has shown that many times. Knifemakers also crink (bend) blades to get them to sit right in the handles. The chemistry and heat treatment make a difference too, just think about how often the backsprings bend when you open and close them. Blades and saws are not designed to be repeatedly deformed though, and their life will be reduced significantly depending on how much bending takes place, where the bend is, and the quality/grade/condition of the steel itself

Smaug · **Reply #3 on:** July 10, 2015, 07:55:08 PM

Short answer: It's steel and not hardened too much, so you don't need to worry about it for several more bends, I think.

If it were really hard (the metal file/saw might be an issue with bending) or aluminum, it would be a concern, but I don't think it is for you.