"more steel, as you pointed out, which can mean more rigidity, which in turn can mean less strength at the edge because of less bending flexibility"
How does that work again, exactly? Adding more steel to an object makes it weaker, because it no longer has as much "bending flexibility"?
You'll have to talk pretty fast to sell that to me.
Let me put it this way, and I really hope this time I come through...: If there is less steel in your lever, whatever you are trying to break with that lever becomes
stronger relative to that lever... And if the metal lever is weak enough to bend under the effort, then it affords you more excess effort without risk of breaking what you want (or don't want) to break...
On the curved belly portion, there is less "other" steel level with the edge portion under stress, so that edge becomes stronger
relative to the available lever... And this
does mean you can afford to apply
more force without experiencing edge breakage... Why not apply less force then? Because our perception is sometimes coarse, so a weaker lever compensates by absorbing too easily applied efforts...
Since the work in my case was cutting wood, and then applying side forces to the edge, the bending of the curved edge afforded much larger excess efforts without edge breakage... (There is also the additional "wastage" factor of my effort being misaligned to the edge by the edge curvature)
If you leverage a door with an iron bar, it will take you less effort than with a bamboo stick, because your effort is wasted in bending the bamboo, and not all your force is applied to the door...
I'll grant you saying the curved edge is
actually stronger is wrong: As a practical matter, all else being equal, it does require far more physical effort to cause chips on it...
It is the same with the tapered blade: It is not stronger, but by wasting your effort in allowing a bend, it does give you more warning of impending breakage, even if it breaks earlier... In addition, the effort you waste bending it has to be added to the effort breaking it, so there is more effort involved
for the same thickness at the break.
You are right that the tapered blade being thinner, it will also break earlier, but then you are no longer making a proper comparison...
For the same reason most aircraft wings are tapered, because bending at the tip absorbs loads that would be otherwise be transmitted directly to the wingroot: When the wing does not taper, the whole aircraft has to be a lot smaller or lighter, with much more rigid wingroots... (And lightly wingloaded aircrafts do skip on tapering the wings, in the interest of lift)
Gaston
