Vehicle protection from artillery shells

[John Kettler]

HerrTom,

Hope my exegesis which follows is coherent and properly assembled. If not, I sure tried hard!

After reading your last several posts, I'm almost dizzy, in part because of the wild oscillations in fragment size, depending on the plot. In one instance you're talking about your focus on a 40 gram frag, with a scale which only goes as high as 60 grams, but on another, the scale goes to 5000 grams! While I'll be the first to admit the performance deficit resulting from my head injury, I believe it's fair to state that back in my defense analyst days I would still have found following your complex argument challenging. Reminds me rather of one of our senior air-to-air guys at Rockwell who got so tired of the usual calculations that for fun he converted them to furlongs per fortnight! Adding to my confusion is that you keep swapping ordnance and that there's no figure number to reference, which would aid in keeping track of which depicts what without requiring heavy scrutiny.

What is clear, presuming I'm correctly interpreting the plot for the blended frag, is that artillery is very good at eating AFVs, especially true for the Russian variety which generally use mild steel for their lower hull. This includes tanks. The situation with APCs was even worse. Combat experience in Afghanistan found muj killing the driver of a BTR-60 by firing into the wheel well on the driver's side at close range. Would further note that the direct hit penetration figure for the lowly 82 would still pose a serious threat to a tank in the event of a roof hit, for there is no way (based on recollection only) those protective housings are 3 cm thick, meaning that anything on the turret roof could easily take a bunch of penetrating hits. If I'm right, this would probably be an issue as much a meter from the detonation point.

Fortunately for me, you seem to have brought it all together in the last post, so let me now ask whether what I think you're saying is what you're actually saying. For if not, I would request further explanation.

Are you saying, for example, that at a fragment density of 0.1/sq meter it takes 30 mm of RHAe to stop frags from the 82 mm mortar . Here, the part that baffles me is how you can have such a ridiculously low frag density from what is a direct hit. Also, I presume, though it's not mentioned directly, that the last plot treats the target as being in the side spray of the frag pattern? If not, what are you trying to convey.

Below is something my trawl for the correct mortar bomb designation (not my strong suit--or any suit) turned up.  YMMV as to usefulness!

Soviet 82 mm Mortar Manual

https://docs.google.com/document/d/1Ubalz784giNaQVm0ytGNR5qLdnjbQeT6ijL2xHYtCzI/edit

One morsel from the preview (can't view or DL unless logged into Google) is this. Two different types of o 832! (O832 correct form?)

"This fragmentation mortar shell, o 832d, is fired from the various 82mm battalion mortars. it differs from the o 832 fragmentation mortar shell.."

Continuing

4 hours ago, HerrTom said:

Now you can compare all of the shells on the same plot!  Science!  Interesting to see that the 203 shell is less dangerous at the same fragment density than the 152mm shell.  This is probably (definitely) because the model predicts the 203 mm shell only producing some 500 shells compared to the 1500 from the 152 mm shell.  That's not to say the 203 is less lethal - if any of those fragments hits anything, it's going to cause a hell of a lot of damage.

Presumably, you are referring to fragments where "500 shells" appears, right?
How did I do? Did I pass the course, or will I have to repeat it when next available? Below is a second fascinating find I made.

 
In furtherance of your excellent unfolding work, though not pertinent to your frag vs armor studies, I came across this while trying to verify the designator for the Russian 82 mm mortar shell. 

Characterization of Explosive Weapons Research Report is a project of the GICHD (Geneva International Centre for Global Demining)

http://characterisationexplosiveweapons.org

Regards,

John Kettler

 

Edited June 4, 2017 by John Kettler

[HerrTom]

49 minutes ago, John Kettler said:

Are you saying, for example, that at a fragment density of 0.1/sq meter it takes 30 mm of RHAe to stop frags from the 82 mm mortar . Here, the part that baffles me is how you can have such a ridiculously low frag density from what is a direct hit.

I admit my nomenclature here was confusing.  What the plots say is that if you take the largest fragment present in that space at 0.1 per square meter, you'll need 30mm RHAe to protect against it.  Increasing that desired density will bring the contours closer to the shell impact, and lowering it will bring the contours further out.  It's really a cross section of a 4 dimensional surface

Perhaps a better way of explaining it is that with the 0.1 fragments per square meter density, a 10 square meter, 30 mm thick, RHA target at that location will see (on average) 1 perforation per shell.

This is one of the weak points of my presentation.  I'm scratching my brain trying to figure out how best to present the data I have, and haven't been able to come up with a better way.

Edit:
Perhaps this will be a bit more enlightening, John:

This plot shows the actual density of fragments greater than 1 gram as they fly away from the impact site.  If it lands directly on you, every square meter will see 1,000 fragments hit it.  Then, by around 10 meters, there's only 1 fragment greater than 1 gram per square meter, and so on.  So to reiterate the above, I specifically looked at what fragment mass can I look at such that the density is always .1 fragments per square meter greater than a certain mass.  I hope that makes sense  

49 minutes ago, John Kettler said:

Also, I presume, though it's not mentioned directly, that the last plot treats the target as being in the side spray of the frag pattern? If not, what are you trying to convey.

Pretty much.  I calculated the plot by taking the maximum penetration calculated at any point at that radius from the shell.  If you look at the contour plots and look for the highest value at any vertical section, you'll get that plot.

49 minutes ago, John Kettler said:

Presumably, you are referring to fragments where "500 shells" appears, right?

Damn! You're correct.  Bah, proofreading is for technical writers!

49 minutes ago, John Kettler said:

How did I do? Did I pass the course, or will I have to repeat it when next available?

You'd definitely have passed if I had been clearer! Thanks for asking for clarifications, I know my mind can get a little crazy. 

---

In other news, I did a quick calculation to compare the results of the 155mm shell from the Protection Provided by Steel and Aluminum Armor Against Fragments from High Explosive Ammunition on the first page of this thread.

From 36x 155mm rounds, their 144 square foot, 3/8" (9.5mm) targets saw 585 hits and 55 perforations at 90 feet (27 meters). My model predicts 101 hits and 48 perforations. I'm not sure how they count hits here, and may be counting impacts from fragments smaller than what my model predicts. Regardless, I think the interesting part is the perforation comparison:

Experiment: 55
Model: 48
Definitely good looking in support!

That's all for tonight!

Edited June 4, 2017 by HerrTom

[c3k]

Excellent correlation between your work and the real life test.

[HerrTom]

Just compared the 1/2" plate from the study.

162 square feet target at 90 feet (27 meters).

Experiment: 476 hits, 41 perforations
Model: 114 hits, 32 perforations

Again, I seem to lowball it, but I'm not sure if that's a bad thing in this case.  I found a paper that said the Mott distribution might not always work out and suggested a few others, but they seem too empirical for my tastes - it makes them less useful in creating general models like I am.  At any rate, Mott seems to underestimate the number of smaller fragments compared to reality (sometimes, it's all very confusing).

[John Kettler]

HerrTom,

Very much appreciate your in-depth reply. Your latest frag density plot provided me the information necessary to truly understand your message, for it is now quite apparent what is being depicted. Not sure what to make of the bizarre to me situation in which your model has only 1/4 the hits of the experiment, yet somehow very closely tracks the number of penetrations. so shall be intrigued to see what further insights emerge as you continue for investigations.

Regards,

John Kettler

[HerrTom]

I did some more reading and it seems Mott is the best for my particular application - as I break down the shell into short sections where the Mott distribution pans out pretty well, while for looking at shells overall, the Wiebull or Held distributions work out better some of the time.

At this point, I'm curious what Steve @Battlefront.com thinks, if anything! 

---

John,

I think it may lie in the Mott distribution underpredicting the smaller fragments.  If you were modeling personnel danger, it may be important, but for the armor penetration models larger fragments are more important.  Thankfully, Mott is pretty good in those ranges, as best as I can tell.  This might account for the discrepancy in the impact numbers - the ones that can actually penetrate the target are accounted for, more or less, but the smaller ones are not.

Edited June 5, 2017 by HerrTom
Responding to John

[c3k]

Agreed: for modelling armor penetration, the smallest fragments are inconsequential. If we were looking at personnel danger zones, then the smaller frags would be of higher importance.

[cool breeze]

All this work you guys have been doing is SO impressive!!  Thanks!

[HerrTom]

Thank you cool breeze.

I guess while I'm attempting to summon people, I'm wondering if this matches the intuitions of @TheForwardObserver and @panzersaurkrautwerfer

Another note/clarification from the plots on page 7 - they may look scarier than reality.  While a BTR would see 10 hits at 0.1 fragments per square meter - those hits still have to hit something important.  Those important bits are somewhat smaller than the vehicle.  Additionally, very few fragments from any single artillery shell will hit the armor straight-on, which is what the plots show.  Add in an impact angle and armor gets even better.

[DougPhresh]

Firing airburt 203mm to no effect on BTR 70s is pretty damn disheartening. I'd like it if you could at least degrade radios and radars. 

[cool breeze]

I think that if BFC does ever change the artillery/tank and especially airburst/tank relationship, at this point they probably owe HerrTom a line in the credits and at least a free copy of the next game   Its amazing how close your results were to the test.

[HerrTom]

6 hours ago, cool breeze said:

I think that if BFC does ever change the artillery/tank and especially airburst/tank relationship, at this point they probably owe HerrTom a line in the credits and at least a free copy of the next game   Its amazing how close your results were to the test.

I wouldn't complain haha!  I think @TheForwardObserver would deserve one too, for without him I wouldn't have even thought to do this.

 

Thanks for the kind words, though.  I haven't forgotten about this!  Just got a bit busy what with work and dogs and a different personal project in translating portions of a Soviet textbook.

A little teaser of the next module I'm working on to better present the data I've assembled:

And, perhaps the best way to compile all of this thread in an easy-to-read way (still very WIP)

[HerrTom]

Another teaser of the 3d representation as I continue to work it:

I'm a little limited by the quality of the model I have for the BTR right now.  I might work on getting a better one with more polygons.

I'm trying to create a geometry-based roll on penetration chances so I can integrate over the entire surface of the vehicle to get essentially a number of penetrations based on an arbitrary impact point for the shell.

... And this includes airbursts! One of the real points of contention:

Anyway, I'll try to answer any questions as best as I can and will otherwise keep you all posted!  

[DougPhresh]

Infantry may occupy, but you just conquered this Gunner's heart.

[Sgt.Squarehead]

Amazing stuff (borderline sorcery from my perspective TBH). 

Edited July 20, 2017 by Sgt.Squarehead

[TheForwardObserver]

4 hours ago, DougPhresh said:

Infantry may occupy, but you just conquered this Gunner's heart.

In 14 years I've never come across anyone that impressed me like he has.  Every battery should have a @HerrTom

[DougPhresh]

 I didn't see analysis of anti-armour applications of Arty like this in school or the battery, even when we got Excalibur we didn't much more on using it on hard targets than "Call KAF to get authorization! Do you know how much those cost?!" 

@HerrTom, where would using precision rounds put the frag pattern from an airburst?

Note to @Battlefront.com: Could we see more arty options in a future engine update?

Illum would make the night battles in WW2 much better IMO (IR for modern titles would help too!)

Smoke pots rather than WP would help with screening and make the Rules of Armed Conflict easier to follow in the modern titles (see: PR disaster of WP in Mosul) 

Cluster shells may be contentious, especially DPICM, but I wouldn't be opposed to seeing them.

finally the ability to adjust burst height, coupled with @HerrTom's frag data could lead to some more control over desired effect on target.

 

Edited July 20, 2017 by DougPhresh

[Sgt.Squarehead]

Great suggestions.....Somewhat unrelated, but smoke generators on tanks are sorely needed too.

[Xorg_Xalargsky]

@HerrTom You're doing amazing work! I've been following it for days, very interesting. This is what makes the CM community so great.

[HerrTom]

Quick little teaser before I head to work:

[HerrTom]

And the work continues... I've added a couple of cool features to the 3d code:

I draw the fragment velocity plot around the burst point so we can get a better idea of where the fragments are heading.

I also made the arrow a bit more visible and introduced rotations in addition to the translations that I am able to do when I load in the model.  This means I can rotate the model any which way I want when I load it in!  I also rotate the shell impact along the Y axis when I do the penetration model to make it easier for me to play around with it after I've loaded in the model.

One of the things I really want to do in the future is introduce variable armor thickness - something which I'm not quite at yet.  The only way I see to do it right now is to manually input each of the several thousand vertices an armor value... which I'm not inclined to do right now!  

I also vectorised some code and it now runs 50% faster!  It's amazing how much faster things are when you do them once rather than a few thousand times!  This doesn't affect you guys all that much but it made me happy - some of the things you can't think could be done in parallel really can!  My tuition for becoming an engineer is paying off!  Oh, wait... that's my job... 

Anyway, here's the result of the recent "build" of the target simulation:

This kills the BTR.  Transparent so you can see just how screwed the BTR is.

And an airburst angled perfectly.  Those 152's will get you if you're close up!

 

Edit: Forgot the other half of that one:

The picture drastically changes if the shell comes in from the other direction.  Only 4 penetrations here compared to 101 from the previous one.

Edited July 22, 2017 by HerrTom

[c3k]

Fantastic!

Obviously, the armor thickness/hardness/angle you're using in the models are going to be important. If you include that information in your final results, well, hmm, I'm not sure if I'd have any other wishes.  

Great stuff...especially the analysis of how the incoming artillery angle and offset at time of detonation makes such a critical difference in airburst effectiveness against armor. (Don't have the nose of the shell pointing at the target when the shell goes "boom"; better to have the target perpendicular to the shell's line of flight.)

[Sgt.Squarehead]

Just a thought, but wouldn't an average of armour thickness over broad areas suffice, I'm presuming this model does not take into account the variable mass of the fragments? This would add 'fuzz' to the numbers which might actually be advantageous for gaming?

 

Edited July 22, 2017 by Sgt.Squarehead

[Armorgunner]

HerrTom

First of all. Its an absolutely fantastic work you have done. What kind of hardnes of the armour are you using? From the 350 Bmp's Sweden bought in the the late, first half of the 90's. I know they had a high brinell hardness of 350-400 IIRC. Which is quite high. Makes the armour strong, but brittle. As a comparison, the Swedish PBV 302 had a brinell hardness of 250-270 IIRC. I know that soviet used high brinell hardness steel on their Apc/ifv's at the time of BMP/BTR/MT-LB.

It can affect the results, because smaller-sized high-speed fragments just bounce away. While heavier slower fragments cause the armor to break? The opposite should be the case on lower brinell hardness. It should be better at resisting the big slow ones, as its tougher and will not brittle. But worse on the high speed smaller ones, that goes throw like a knife in butter.

And I can add to that. That the armor on the BMP resisted the .50 AP bullets of the time, even in the side. We (Sweden)  belived that the .50 should be able to penetrate the side armor. At weakspots it did of Course. But the armor was tougher than expected against smallarms, and HMG. But brittle when the limitation was met.

Edited July 22, 2017 by Armorgunner

[Armorgunner]

I can add to that. That now, 25 years later, I don't remember the different ranges that the .50 was tested against the BMP though. But probably from pointblank to eternity, if it was the usual testing program.

And it could been only the "normal" or "expected" combat ranges that i was informed of though, its a long time ago ( I left the Army sometime in the late first half of the 2000-2010) The expected combat ranges was quite short anyway, in our woodland country. 100-500 meters for most encounters. Even though the tank, and mechanized brigades mostly traind for encounters a little bit further away. The motto was always: Firepower over protection. On the attack of a Soviet/Russian beachhead.

Edited July 22, 2017 by Armorgunner