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Old 09-01-2019, 03:20 PM   #11
Anthony
 
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Default Re: Video of arrows vs. armor using period materials

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Originally Posted by ak_aramis View Post
Keep in mind, steel penetration isn't directly linear, and sufficiently deep dents break bones and/or cause metal fatigue.
Sure, but there's a fairly distinctive 'partial penetration' phase before the attack goes all the way through, and none of those hits were at it (you'd see tearing starting at the bottom of the dents).

As far as behind-armor blunt trauma goes, that could easily be occurring with the dents they showed, and in any case they didn't have a testing setup that would be able to answer how much risk it is.
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Old 09-01-2019, 05:40 PM   #12
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Default Re: Video of arrows vs. armor using period materials

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Sure, but there's a fairly distinctive 'partial penetration' phase before the attack goes all the way through, and none of those hits were at it (you'd see tearing starting at the bottom of the dents).

As far as behind-armor blunt trauma goes, that could easily be occurring with the dents they showed, and in any case they didn't have a testing setup that would be able to answer how much risk it is.
In many cases, the cracking begins on the far side, not the impacted side. (I've actually seen spalling in destructive testing with an axe that I was present at.)

Further, they did mention scratching

A 1/2" deep, the dent potentially breaks a rib, either on the deformation, or a following hit; 120 J is well capable of breaking a rib (it's approximately the standard .22lr energy), even through padding.

Plus, 160 to 200 is a 25% increase in energy, which should be around 1.25^0.75 times the penetration.
The largest dent looked to be about 1/4"... but add better energy transfer from deeper scratching...

just enough variable to make the 200lb worth testing.

Also would be interesting to see a competent slinger with a lead bullet.
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Old 09-01-2019, 06:37 PM   #13
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Default Re: Video of arrows vs. armor using period materials

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None of the 160 lb shots were anywhere close to penetrating, 200 lb might give you some deeper dents but that's about it.
Very likely, but I would have liked to see it demonstrated anyway. While they had the rig set up and an archer on hand capable of shooting accurately with such a bow there was an opportunity to do the test and show the results. I would have liked to have seen it done.
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Old 09-01-2019, 06:37 PM   #14
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Default Re: Video of arrows vs. armor using period materials

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Plus, 160 to 200 is a 25% increase in energy, which should be around 1.25^0.75 times the penetration.
Unless using heavier arrows it will be less than +25%, and I don't know where you're getting a 0.75 exponent, real world scaling for increasing velocity is going to be a complex curve (there's actually a real chance that improving velocity wouldn't increase penetration at all, penetration in this case appears limited by the durability of the arrow).

It would probably be more practical to just test with a modern compound bow, once the arrow leaves the bow the difference won't matter and you can get the same energy at less than half the draw weight.
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Old 09-01-2019, 08:26 PM   #15
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Default Re: Video of arrows vs. armor using period materials

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Unless using heavier arrows it will be less than +25%, and I don't know where you're getting a 0.75 exponent, real world scaling for increasing velocity is going to be a complex curve (there's actually a real chance that improving velocity wouldn't increase penetration at all, penetration in this case appears limited by the durability of the arrow).

It would probably be more practical to just test with a modern compound bow, once the arrow leaves the bow the difference won't matter and you can get the same energy at less than half the draw weight.
The 0.75 exponent is rounded from that used in several texts on steel penetration depth, and was used independently by several different game designers doing seriously simulationist work. Greg Porter, as well as others. as a rule of thumb, it's close enough. Greg uses a more precise one in 3G3. I've seen it in other sources, as well.

Also, you don't need to increase the projectile mass any - it's already sufficient to destroy the projectile's integrity on impact (that was a surprise to me). Velocity is a better carrier of the energy, and since the projectile is doing secondary shrapnel damage (wood shrapnel is known to be a killer, and is commented upon by several naval historians; we see plenty of it from those arrows...).
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Old 09-01-2019, 09:25 PM   #16
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Default Re: Video of arrows vs. armor using period materials

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Also, you don't need to increase the projectile mass any - it's already sufficient to destroy the projectile's integrity on impact
That would be the reason to increase projectile mass -- to increase the amount of energy required to destroy the arrow. The arrow breaking is significantly reducing the penetration of the arrow, because any kinetic energy still possessed by the shaft after it breaks is not helping penetration at all.

If the 0.75 power comes from G3G, it's probably a translation of the DeMarre penetration equation. Which is intended to model the performance of TL 6 naval cannons, applying it to arrows is a stretch.
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Old 09-02-2019, 09:16 AM   #17
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Default Re: Video of arrows vs. armor using period materials

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Unless using heavier arrows
The rule of thumb I found in research is that a hunting arrow should have a mass of between 10 and 15 grains per lb of draw. There is an overlap zone for 160 and 200 but you'd have to have been on the higher end of mass for 160.

If I was increasing my pull by 25% I'd increase my arrow mass by the same. If I had been at an optimum mass for 160 I'd probably stay at the same velocity for 200 lbs and see a 25% increase in KE.
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Old 09-02-2019, 09:39 PM   #18
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Default Re: Video of arrows vs. armor using period materials

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The rule of thumb I found in research is that a hunting arrow should have a mass of between 10 and 15 grains per lb of draw. There is an overlap zone for 160 and 200 but you'd have to have been on the higher end of mass for 160.

If I was increasing my pull by 25% I'd increase my arrow mass by the same. If I had been at an optimum mass for 160 I'd probably stay at the same velocity for 200 lbs and see a 25% increase in KE.
Higher speed has advantages in penetration, in that it results in less spread per unit time of the penetrator, provided it's harder than the target. The 11% increase in speed may or may not be enough to matter, I don't know enough to judge. We are seeing plastic deformation even in the case-hardened ammunition, and in the target (denting is a plastic deformation); the acceleration of the target metal by the penetrator is also an acceleration...

Having watched the video, if one were to increase the mass, I'd do it on the head alone (increased length), not in the wood- the shrapnel effect is quite valuable against formations. It doesn't matter if Sir Tank doesn't take the shrapnel if Sir Guy next to him has his eye, jugular or carotid impaled with splinters.
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Old 09-03-2019, 09:21 AM   #19
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Default Re: Video of arrows vs. armor using period materials

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Higher speed has advantages in penetration,s.
You can not necessarily increase speed freely. Bows and arrows have hard limits on speed due the mechanical limits of the elasticity of the bow/arrow system. I haven't heard of an arrow achieving over 250 feet per second. After you reach that level increasing KE comes from increasing mass or it doesn't come at all.
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Old 09-03-2019, 10:09 AM   #20
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Default Re: Video of arrows vs. armor using period materials

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Higher speed has advantages in penetration
Bow performance has very heavy falloff as you reduce arrow weight; more and more energy is consumed moving the body of the bow.

If you have a bow that's at 50% efficiency, which looks to be about where the sample longbow was, increasing draw weight by 25% increases the weight of the active elements of the bow by 25%, which will reduce efficiency from 50% to 44%, for a real energy improvement of only 11% and a 5% increase in velocity.
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