Yes, I do know this thread is more than the two years old it was last time someone necroposted but it comes up on google hits and is full of such misinformation that needs to be addressed.
One thing that makes a so called "tanto" tip (no matter if it's an americanized, sharp angled one or a more traditional rounded one)
Let's be clear, any of the varieties of tanto have more in common with a FS knife point than they do the chisel like americanised chisel tip (which I won’t call a tanto here). Their tips are both more acicular than the chisel and have a more gradual taper. Lumping the two together doesn't help your argument.
more suitable for piercing armor than a blade that becomes gradually wider from the tip to the hilt (for example a Fairbairn/Sykes style dagger), other than that the dagger tip is more fragile,
Here is why lumping then together doesn’t help: tanto (the true kind)
are rounded and do become gradually wider from the tip to part way along the blade. So in less than one sentence you’ve said
traditional tanto are more suitable for piercing armour than traditional tanto .
The thickness is the only benefit. Needle dagger tips are fragile but you have to remember that the FS knife was not designed with armour in mind, just cloth and flesh. Older dagger designs for armour penetration do have quite slender tips but are thicker and stronger than the FS knife and worked quite well for piercing mail.
is that since the tanto blade has the same width all the way up to the tip and doesn't taper into a sharp point until just before the front end of the knife, you can use the initial velocity of a violent hard stab to first force the tip of the blade through the armor.
Once the tip part of the blade is through the armor, it doesn't take so much more force to push the rest of the knife into the body, since the initial impact of the tip already has ripped up a wide enough hole in the armor to give room for the rest of the knife, since the blade never becomes any wider than the tip part.
Please note “violent hard stab”. It does have to be hard as will be noted. Also, where is this imaginary chisel point that doesn’t have a blade that gets wider? I’ve just measured one that was about 30% wider at the hilt than the end of the point region (at what equates to a sword’s yokote if that term means anything to the reader). This is kind of important. It means about 75% of the blade’s width occurs in the first few millimetres.
The second paragraph of that quoted section above contains just about 100% of all the correctness in the quoted post. Once the hole in the armour is made resistance to further penetration is lower.
Once...
And then you have to do damage to the target behind the armour, unless you’re just trying to perforate a car for some inexplicable reason.
A Fairbairn/Sykes style dagger is more effective for making many quick deep stab wounds to an unprotected area, but if you were to use it against an armored body part, what would happen would probably be that when you stab the target, the thin tip might penetrate the armor nicely at first, but once the tip is through and the momentum is lost, it's a lot harder to force the rest of the knife through, since it becomes gradually wider towards the hilt.
You would have to push the knife through the armor.
Let’s be clear again, no matter the blade shape they
all have to be pushed through this hypothetical armour. The only difference is what proportion of the blade and what they do on the other side.
If you instead have a tanto, all the armor piercing that you have to do takes place at the impact of the stab (when the attack is as strongest), and after that, you only have to push it through flesh.
You have completely and entirely overlooked the fundamental point of your own argument, the chisel is
wider and
less acute than the FS knife and most pointed knives.
What you got right is that the largest force (I presume that’s what you meant by violent hard stab above) “takes place at the
(start of the) impact of the stab” (I added the emphasised words here to make things clear). Because the chisel blade is less acute the impact force is spread over a larger area making the pressure less. The blunter an object, the less able it is to pierce. The sharper an object the better it can pierce up until it suffers mechanical failure at which point it rapidly becomes a blunt object. The blunt object with more material in a given region is going to absorb the dynamic load better, less bending or rupture—but you have already excluded the “dagger tip is more fragile” argument from consideration. The large area of contact and the resulting considerable amount of armour material that has to be ruptured in a short amount of time makes for very large resistive forces (which the thicker tip is able to accommodate).
When a fine point like a dagger hits a target the pressure is huge because the impact force is concentrated in a tiny area. Because the target area is initially small the resistive forces are correspondingly small so it does “penetrate...nicely at first”. Writing that “once the tip is through...momentum is lost (and it is a) lot harder to force the rest of the knife through” has no meaningful basis in the argument: all knives are going to lose momentum, what matters is the rate. Allowing that what you mean is “the dagger loses momentum which is gained by the target”:
Change in momentum, called impulse, is proportional to the size of the force and the duration of the force. Small resistance from the target means small loss of momentum from the dagger. As momentum is the product of mass and velocity, the knife is not gaining or losing mass and the momentum loss is small the knife retains high velocity. This high velocity equates to high kinetic energy and as anyone who has studied even a little should know it is the energy that leads to penetration.
Yes, the dagger width does increase but it does so gradually. The increase in resistive forces is thus gradual and the loss in momentum likewise. The edges of the blade and the thickening of the spine serve to continue gradually widening the entry wound as required until the energy is spent.
With the chisel and its rapidly increasing impact area there is a very high upfront cost. A lot of work has to be done penetrating the armour leaving comparatively little energy for anything else.
The actual armour penetration ability of any particular knife or dagger is going to depend upon the armour it is attempting to penetrate, if the tip is mechanically strong enough to do work on the armour without failing, and
what lies behind the armour, something which the chisel point fan boys fail to appreciate when touting the auspices of the chisel point and its ability to pierce a car’s sheet metal. It’s great if the tip pierces the armour, not so great if it stops moving before it can do any damage to the target, not so great if by being blunter it leads to momentum transfer to the target, losing energy by knocking the target back rather than penetrating the armour. (This is, of course, how armour works, spread the load so that the impact energy is dissipated over a larger area leading to less damage to the target.)
Momentum transfer is great for hammers and maces where you want as great an impulse as possible, not great for blades where you’re relying on penetration and this is less likely to be achieved with a wider, blunter tip. I’d love to see some rigorous tests of knife points versus free standing body armour with meat like material behind it, particularly those “stab proof” vests, to prove me either right or wrong, mostly because they would be interesting and partly because I’m confident of my understanding.
The very fact that the chisel point blade actually has a grind on both sides of the point to bring it to a fine edge should tell everyone with at least half a brain exactly what simple machine is being applied to do all the penetration work. If the “big tip/narrow waist, make a big hole at the start/ rest slips through unmolested” argument was correct all armour penetrating devices would consist of a broad, dull head with a narrower section following, exactly like driving a flat-head nail head first.
... Resurrecting those dead threads... I was following this thread for a long time. I wish my arrogant Russian friend from California wasn't banned so I can read more twisted views on "Americanized" things but unfortunately he's gone... 