Puncturing points-A question

[Dylan Asbury]

I remember a long time ago, reading an ad in, I believe it was Brigade Quartermaster or one of those other catalogs that sell tactical knives and such things. One of the products was a titanium-bladed knife with a rather unconventional "point". Rather than a point in the usual sense, it had a squareish tip, sharpened and tapered very slightly so instead of a triangular point it had more like a trapezoidal sharpened edge at the end. The ad claimed that such design possessed greater penetrating power than more conventional designs and I was curious as to whether anyone out there with a greater background in physics or geometry than mine might be able to, even in theory, verify or disprove the idea.

I wonder if this is really an innovation or just a good sales pitch? If the edged tip provides better performance than a conventional one, is it significantly better? or is the improvement so marginal as not to matter? Would this be the sort of thing that would benefit a short-bladed weapon significantly more than it would benefit a sword? And, finally, would the knife's being made of titanium account for it being a better penetrator more than the shape of the blade? I'm unfamiliar with titanium's physical properties as i've never handled anything made of titanium. I know it is supposedly lighter than steel, more flexible, and equally durable. other than that, I don't really know.

Thank you for your answers!
-Dylan

[Jonathan Newhall]

Well, the triangular point is definitely more efficient in at least one way: it has to displace less mass. Contrarily, the larger the point's displaced mass, the more difficult it is for the wound to heal.

I've only a rudimentary knowledge of the damage mechanics from stabbing, though (and primarily based on the evolution of bayonet design at that), so perhaps somebody else can take it from there.

[Stacy Clifford]

It depends on what you're trying to penetrate. The physics of stabbing are really pretty simple, the more slender the piercing object, the less mass it has to set aside and the easier it will slide in. Needles are pretty much the ultimate if you're stabbing soft flesh, followed by stilettos and other very slim blades. If you're trying to punch through armor then the structural integrity of the knife comes into play, because you don't want it to break or bend as you're trying to penetrate. Knives of every description accomplish this by having a thicker spine, either along the back of a single edge knife or down the center of a dagger. "Penetrating power" sounds a bit deceptive because a more massive knife is going to encounter greater frictional resistance, but it allows you to hit harder to compensate without breaking the knife. A trapezoidal tip (sounds a bit like a tanto knife) doesn't sound like it does anything for the friction problem, so I would assume that the blade is architecturally very strong to resist breaking under intense impact.

Titanium gets a lot of hype, but that's mostly what it is, hype. Titanium is as structurally strong as steel at a considerably lower mass, which makes it fantastic for load-bearing applications like airplane frames (like the SR-71) that need to be lightweight. However, titanium is not as hard as good carbon steel, which means it dents and scratches easier and won't hold an edge as well. Also, when it comes to swords, there's something to be said for having extra mass. Remember Force = mass x acceleration. If I take away 40% of the mass of a 3 lb. sword by using titanium instead of steel, does that let me swing it 40% faster to equal the same amount of force? At low weights like that, no, probably not, you're going to swing 3 lbs. almost as fast as you're going to swing 2 lbs., so in reality with a titanium sword you would probably lose striking force, which translates to less cut penetration or denting of armor, as well as less mass to oppose a blow defensively, all bad things. Steel is actually better for swords, and probably for knives as well due to the need to hold an edge. If anything I'd rather have titanium armor than a titanium sword because that's where its lightness and strength would have better advantage.

Read this if you really want to get in depth on the physics of it:
http://www.thearma.org/spotlight/GTA/mo ... mpacts.htm

[Dylan Asbury]

Thanks, your answers have really helped clear this up. Based on what Stacey said, it really sounds like titanium would be more advantageous for a knife than a sword as a knife doesn't need the mass for cutting strikes that a sword would. Either way, your response basically confirms what my suspicion was in the first place. The unconventional form, while perhaps more devastating, isn't devastating enough, in my opinion, to warrant use in a sword. Sure, it might do more damage. But the traditional form is certainly damaging enough, perhaps more so, since the idea was to achieve depth and accuracy in a thrust, rather than a wider wounding hole. (at least for swords. As i understand, the pole weapons are substantially larger to be able to incapacitate horses and armored men.)

Thank you again, I was just trying to ascertain if there was something special going on here or just a slick sales pitch around an ordinary knife.

[Jonathan Newhall]

It depends on what you're trying to penetrate. The physics of stabbing are really pretty simple, the more slender the piercing object, the less mass it has to set aside and the easier it will slide in. Needles are pretty much the ultimate if you're stabbing soft flesh, followed by stilettos and other very slim blades. If you're trying to punch through armor then the structural integrity of the knife comes into play, because you don't want it to break or bend as you're trying to penetrate. Knives of every description accomplish this by having a thicker spine, either along the back of a single edge knife or down the center of a dagger. "Penetrating power" sounds a bit deceptive because a more massive knife is going to encounter greater frictional resistance, but it allows you to hit harder to compensate without breaking the knife. A trapezoidal tip (sounds a bit like a tanto knife) doesn't sound like it does anything for the friction problem, so I would assume that the blade is architecturally very strong to resist breaking under intense impact.

Titanium gets a lot of hype, but that's mostly what it is, hype. Titanium is as structurally strong as steel at a considerably lower mass, which makes it fantastic for load-bearing applications like airplane frames (like the SR-71) that need to be lightweight. However, titanium is not as hard as good carbon steel, which means it dents and scratches easier and won't hold an edge as well. Also, when it comes to swords, there's something to be said for having extra mass. Remember Force = mass x acceleration. If I take away 40% of the mass of a 3 lb. sword by using titanium instead of steel, does that let me swing it 40% faster to equal the same amount of force? At low weights like that, no, probably not, you're going to swing 3 lbs. almost as fast as you're going to swing 2 lbs., so in reality with a titanium sword you would probably lose striking force, which translates to less cut penetration or denting of armor, as well as less mass to oppose a blow defensively, all bad things. Steel is actually better for swords, and probably for knives as well due to the need to hold an edge. If anything I'd rather have titanium armor than a titanium sword because that's where its lightness and strength would have better advantage.

Read this if you really want to get in depth on the physics of it:
http://www.thearma.org/spotlight/GTA/mo ... mpacts.htm

A quick note, it should also be known that energy = 1/2mass x speed^2, making speed four times as important in energy. Force is often more important for things like penetration, but energy is also key - one m/s faster is worth four kilograms more mass for energy (assuming both factors are nonzero).

[Stacy Clifford]

Yes, true, I was just doing some quick calculation in my head; I knew it wouldn't be perfect but it conveyed the idea, and he was asking about penetrating power. It would be cool if we could come up with some empirical tests for this kind of stuff without spending thousands on titanium blades.

[Adam Bodorics]

Ti sucks if you use it for anything else than modern vehicles or armour. The only true advantage of Ti over steel is that Ti is much more corrosion resistant - other than that, nothing. You won't break a good combat knife if it's made from anything better than mild steel, so strength is not an issue AND you can resharpen carbon steel blades on a simple rock while you'll spend sweaty hours with Ti to make it sharp AND making knives out of carbon steel is considerably easier than making them out of Ti. Does it worth the corrosion resistance advantage?

Flat points are often said to cause more damage. That's not exactly true. They can TAKE more damage. That point design is useful if you want to use your knife as a prybar though, which you shouldn't in the first place. Against flesh a good knife is more than enough - you can't really inflict more damage than what you can do with a comma cut.

BTW, check out historical blade designs - if you can't find a modern design among them, you probably should not use that modern design. We tend to think greatly about ourselves, but you can't really surpass the accumulated knowledge of the I-gut-you-with-blades era.

[Greg Coffman]

The knife in question, was it just a tanto knife like this one?
http://www.northamericanknives.com/files/1788248/uploaded/Kb1245.jpg

This is an Asian blade shape. The knife manufacturer/marketer might just be trying to hype up their knives as exotic or special because eastern martial arts = cool or better.

[Steven Ott]

That is a good knife btw

[Steven Ott]

The bowie knife has really come to prominence in the last few centuries. I don't know if it's european, asian or native american in origin but it's a great design.

[RayMcCullough]

One thing to consider on penetrationaand bad wounds are spikes. Daggers that are spikes. They penetrate well and leave ugly wounds that will get infections easier than blade wounds that close after withdrawing. The spiked daggers were outlawed after WWI. Alot of the daggers in Europe are spikes.

The Tanto is supposed to have the mythilogical penetration of a katana because it has the same point. I have seen that line given for tanto knives before. That point is better for cutting than stabbing.

Later

Ray

[Stacy Clifford]

The bowie knife has really come to prominence in the last few centuries. I don't know if it's european, asian or native american in origin but it's a great design.

Well being a Texan, I have to point out that the Bowie knife is named for Colonel James Bowie, a famed knife fighter and adventurer in the 1820s-1830s who died in the Battle of the Alamo. The most accepted story of its origin is that the original was designed by his brother Rezin and the design was improved to its current form by James himself and popularized by his exploits and reputation.

[Greg Coffman]

Well being a Texan, I have to point out that the Bowie knife is named for Colonel James Bowie, a famed knife fighter and adventurer in the 1820s-1830s who died in the Battle of the Alamo. The most accepted story of its origin is that the original was designed by his brother Rezin and the design was improved to its current form by James himself and popularized by his exploits and reputation.

Of course, the design of the Bowie knife was not revolutionary. Design elements, like a the clipped point had been around for a while. I am constantly impressed by the similarity between the Bowie knife and the messer. Perhaps the Bowie knife was a "rediscovery" bred from requirements of a all-purpose utility and fighting knife, the same requirements which had led to the development of the messer centuries before.

[Stacy Clifford]

I believe the unique aspect of the Bowie is having a sharp false edge on that clipped point, though I agree the clipped point itself isn't completely original. Bowie is a great modern example though of weapon design directly linked to the skill and knowledge of a proven warrior, as we often talk about the feedback loop between swordsmen and swordsmiths in the Renaissance and earlier times.