Comparing airplane propellors to knife blades is like comparing the ditch in front of my house to the Grand Canyon. There is a world of difference between the two. Is anyone actually going to come up with empirical evidence showing that sanding or buffing a knife blade lengthwise vs. perpendicular has ANY effect at all on its strength?!? Heck, employing that kind of "science", we should all make blades with spines like an I-beam, clearly that's much stronger!
With all due respect, I'm in the camp that views buffing as an aesthetic choice, and one that increases corrosion-resistance. That's it.
Comparing airplane propellors to knife blades is actually a pretty good comparison. The propellor
blades are frequently shaped like unsharpened knives (convex ground), albeit more symmetrical. These blades chop the air essentially, which would correspond to normal cutting of a knife blade. Additionally they have a force exerted on them perpendicular to the plane of rotation of the blades, which would correspond to lateral loads on a knife (using it like a pry bar essentially).
As for your analogy, assuming your ditch was formed via natural means, then the grand canyon and it have a fair amount in common. Both were likely formed by erosion from a body of water passing through it. There are some differences, such as what the surrounding land is made of and the amount of water flow, but the underlying process is the same. The different circumstances don't change the mechanism that creates the ditch, they just change the speed and degree to which it occurs. You could think of these different circumstances as material properties and degree of use in the propellor to knife comparison.
Now if the ditch was man made then your analogy is completely invalid, since you're then comparing a natural process to a man made process, whereas both propellor and knife are man made.
If you're looking for empirical evidence of this effect in just a knife blade, then you aren't likely to find it. However, my guess is that you can find it with respect to laboratory test specimens using steel. You just have to apply the lab findings to your particular use of the materials.
If you had said that you believe that the effect is negligible and not worth the effort, then I would've agreed with you, but you're implying there is absolutely no effect, with no proof what-so-ever.
I-beams aren't stronger, they're more efficient at resisting a bending moment in one direction given their weight. Not to mention, fullers are frequently used on swords to reduce weight without drastically reducing the ability of the blade to withstand a blow.
I've found an academic paper detailing the effects of surface roughness, grain orientation, and residual stresses on the fatigue limit in 304 stainless steel.
Modelling the effects of surface finish on fatigue limit in austenitic stainless steels by Kuroda and Marrow. It won't give you exactly the proof you're looking for, but the cited resources should give you a great place to find the proof.
So my question for you is, where is your proof that it doesn't have an effect? I've cited tons of reasons and theory behind why it does have an effect and all I've heard to the contrary is stuff like "No I don't think it has an effect."
