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Armor Penetration Performance vs. Range to Target?

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#22
[RO]Wilsonam said:
Oh noes... we're about to spin off into penetration equations. Fascinating stuff - but WHAT a ***** :)

Go for it, guys...
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Hi Alan:

It's all part of understanding what is coming from where. I’m not suggesting anyone use the DeMarre equation given what is entailed in generating accurate predictions. To use it accurately entails correlating K to actual ballistic test results. That was how it was originally intended to be utilized. DeMarre knew from extensive experimentation that there was a clear relationship between mass, impact velocity, thickness and shell caliber. Krupp knew the same thing; as did Thompson; as did Milne; as did ARTCM. All pretty smart dudes. They all came to similar conclusions and developed similar equations for predicitng plate penetration. It is no different than Newton's F=Ma in the since that a trend exists and a formula is developed to explain the trend -- the formula being based upon observation, experimental results and the dreaded scientific method. But I would say starting cold with the DeMarre EQ without ballistic test data in hand and thinking one might get reasonable predictions is rather silly. That is the track most folks take and why they sour on the use of DeMarre. Heh heh -- but to discount DeMarre outright as a crock is equally silly. :D

Just for fun, what is the basis for the slope effects you used in RO?

All the best
Jeff
 
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#23
Shurek said:
******Shurek ducks behind wooden fence. Good thing there's no shell penetration on static meshes :p:D:p:p:p:p
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heh heh. You have to shoot the static mesh above, and directly behind the fence with HE. Than maybe some of the splash will hit the guy hiding behind the fence.

If you allowed penetration of static meshes in games it would create a fair bit of commotion from most computer game players. Most game players seem content to think 0.50-caliber AP -- or even ball for that matter -- can't touch them as long as they hide behind a brick wall. Seems like BF2 or some such thing was taking a more serious look at walls and such and the ability of small caliber projectiles to penetrate these things.
 
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#27
K is relevant to hardness and toughness, both obliquity and t/d influence toughness, so K is NOT a constant for a specific armor, but we can simplify this issue by regarding k as a constant because when t/d is not very low or high, de marre equation's accuracy is acceptable.
The big problem is n, we can only adjust n for every satuation such as AP vs. RHA or APCBC vs. Cast, or HVAP vs. RHA, Of course it's time consuming. BTW,we should deal with the projectile normalization phenomenon.
 
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#29
[RO]Wilsonam said:
"Normalization" is dependent on the round - it is one of those constants that needs to vary dependent (primarily) on the incoming projectile's ogive configuration :)
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Normalization in the context of my posts refers to multiple data bases and how the information within these data bases was derived and how to integrate several sets of information such that apples are being compared to apples. One such aspect that folks typically wish to compare are projectile penetration capability from differiing Nations.

As we know, different Countries employed different pass\fail criteria for determining either plate performance or projectile performance. The Germans Employed GS and GD limit; the British used CV, w/r as well as several other criteria, The United States used Army Limits BL(A) and Navy Limits BL(N) as well as protection limits BL(P); The Soviet used IP and CP limits; etc. Some folks like to get hung up on the subtle contrasts between the varying test specifications utilized by different nations in determining how much armor it takes to stop a given ballistic attack; or how much armor a given projectile can defeat.

Don't get me wrong -- there are differences, but they tend to be rather subtle and the error invoked in such contrasts is typically far overshadowed by folks inability to correctly determine down range velocity decay and slope effect. People that dabble casually often want to concentrate on a niggling error sources that might result in a +/- 1 or 2% contrast in limit velocity when their slope effects or Vdrop model is already invoking a 20% to 40% error in limit velocity. No sense of proportion. Smart guys ala DeMarre and Milne and Thompson have already done the parametric studies for you. The results being that the majority of error evloves from incorrect input for the most critical parameters entailed in predicting projectile penetration or plate resistance. The parameters are that are most critical are: mass, impact velocity, plate thickness, obliquity, projectile caliber, and an empirical coefficient. In other words if you can't nail down slope effects and velocity decay properly why do you care about whether the plate is BHN250 or BHN350? Focus on the basics than hone the design.

Yes -- head\nose shape of the projectile also affects penetration capability. The effect varies with t/d and obliquity. For example tests using flat head projectiles indicate they are much more efficient in low obliquity and low t/d events than projectiles with an ogival shaped head\nose. Conversely at low obliquity and t/d near unity the ogival head\nose is much more efficient than a flat headed projectile. At high obliquity, a flat head\nose projectile is less prone to ricochet than a projectile with an ogival shaped head\nose.

Having said all that, most countries during WWII (even WWI for that matter in terms of Naval Armored piercing projectiles) had optimized penetrator head shape (crh if you like). In other words the crh on German AP is relatively similar in geometry to British, Soviet or American AP.

The head shape (crh) on plain Jane AP was a compromise in terms of both exterior ballistics and terminal ballistics. Both aspects needed to be considered in design – i.e. down range velocity decay from ballistic drag combined with head shape that would provide best performance against armor plate. Don't kill possible impact velocity in favor of bluntness.

Use of windscreens/ballistic caps in APC and APCBC allowed the projectile designer the best of both worlds in that he could use a blunter head\nose shape on the penetrator without suffering the ill effects of a poor ballistic coefficient (high drag) associated with a blunt headed penetrator. In this case the windscreen\ballistic cap has a rather high crh – elongated ogival or conical shaped windscreen. But again, nose and head shape – crh -- of the penetrator portion of APC\APCBC between the various Nations producing ammunition during WWII is not hugely different. They were all working against the some constraints and optimizing head shape in a similar manner.

Soviet APBC is sort of a different animal than AP or APC\APCBC.

The long and short being that yes, it is true that head shape effects penetration. If I test a penetrator with crh=0.5 vs. crh=1.4 I will see significant contrasts in penetration characteristics with respect to t/d or obliquity. But the UK, USA, Soviets and Germans all experimented with and established relatively similar head shapes in their plain jane AP. USA, UK and Germany also used similar penetrator head shapes with their respective versions of APC\APCBC. In this sense I think it more important to distinguish between classes of projectiles rather than subtle contrasts in crh within a certain class of projectile. I would therefore focus on the differences between classes of projectiles. Plain jane AP vs. those of APCBC rather than AP with a crh=1.4 and AP with a crh=1.43. I would also focus upon contrast between AP vs. FHA, AP vs. RHA and AP vs. Cast as well APCBC\APC vs. FHA, APCBC vs. RHA, APCBC vs. Cast -- same again for APBC vs. each of the major plate types -- same again for HVAP, Arrowhead, APCR and APDS.
 
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#30
Glen said:
K is relevant to hardness and toughness, both obliquity and t/d influence toughness, so K is NOT a constant for a specific armor, but we can simplify this issue by regarding k as a constant because when t/d is not very low or high, de marre equation's accuracy is acceptable.
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Well good luck with that assumption :D .

I guess what I might suggest is studying some of the work conducted by Milne during and after WWII. Milne recognized that the DeMarre Equation required some tweaking in order to account for improvements in armor and projectiles as well as design trends and battlefield trends.

Recall when DeMarre first developed his equation -- 1870'ish. Proving requirements for naval armored piercing projectiles of the period were normally conducted at zero obliquity or at very low obliquities during DeMarre's days. DeMarre's Equation reflects this. Moreover, naval engagements of the period were thought to involve relatively flat trajectory hits on ship's side armor. Falklands Island, Dogger Bank and particularly Jutland showed that fire control and optics had evolved sufficiently such that long range plunging fire and its resultant higher obliquity hits on side armor and deck armor was now the norm in Naval combat. Post Jutland, projectile testing specifications began shifting toward proving requirements at higher obliquities -- such as 20-degrees and 30-degrees. We see 30-degrees as a sort of constant in testing up to and into WWII.

Milne's work reflects testing trends and tank design trends in which higher obliquity armor and ballistic testing at higher obliquities had become the norm rather than the exception. The results of Milne’s work showed that DeMarre's Equation was still relevant, but that the empirical coefficient does not remain constant with obliquity.
 
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#32
The following is a simple, but good example of effects of projectile head shape on limit velocity and what I am referring to in my above post. Hopefully it will provide a bit more insight into what I am jabbering about.

The attached table and graph represents firing trials conducted by the Dahlgren Proving Grounds during WWII. The intent of the experimental program was
 
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#35
[RO]Wilsonam said:
Interesting point, Jeff. I'm always happy to be able to discard factors with limited/negligible effect :) Anything to simplify the math down!

Any idea how this works out for larger caliber rounds such as the Soviet 85mm? At the time, the Soviets seemed to take quite an interest in this?
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Hi Alan:

Sorry for the late reply. Was busy with family and turkey week.

In regards to Soviet APBC, I would lump it into a seperate class. See above. APBC is sort of an odd duck, but not excessively so. The Soviets sort of gave up on the idea of rigid projectile penetration and an intact nose during plate perforation at higher obliquity. The nose of APBC, and even certain types of AP, was intended as a sacrificial element during plate perforation. Sort of analogous to the penetration cap used in APCBC.

Anyway, there is sufficient experimental data detailing both Soviet APBC & Soviet AP firing trials, as well as flat nose projectile testing conducted by the USA and UK (and limited German research materials) that I have obtained through great efforts and expense such that a reasonably accurate assessment of projectile perforation capability at a wide variety of obliquities can be conducted. I would like to plant this seed in your thoughts; It is of interest to note that the Soviets switched gears post war and began developing standard APCBC designs for their major classes of tank main guns -- ala 85mm BR-367, 100mm BR-412D and 122mm BR-472D. My guess -- based upon the look of these penetration capped projectiles and conical windscreens -- is that the designs were heavily influenced by German Wartime pzgr designs. But that is just a guess. The designs may have been developed independently -- after all the Russians were the first designers to utilize penetration caps on Naval armored piercing projectiles.

I think the best bang for your buck would be to focus upon major classes of armored piercing projectiles vs. the major classes of armor plate. The focus should be on reasonable VDrop assessments and slope effects as they apply to four major projectile groups and four potential armor types.

AP vs. RHA, Cast, FHA and HHA
APC\APCBC vs. RHA, Cast, FHA and HHA
APBC vs. RHA, Cast, FHA and HHA

Than -- depending upon the historical context of the simulation -- hyper velocity projectiles. LRPs, HVAP, APDS etc. vs. the various armor types.

There are tons of whistles and bells that folks want to get hung up on -- AP shot vs. AP Shell -- plate quality -- ogive shape -- nose hardness -- blah blah blah. All can be of some importance. But their relative contribution to the problem is typically masked by peoples inability to accurately model down range velocity and slope effects. Ok -- I said it again :D


If I were you, I would also put a great deal of thought into modeling behind armor effects. These are actually a tad more complex to model in a realistic manner than projectile penetration capability. Damage points and vehicle "health" appear to be hangers on from previous obsolete game programs. They are not the best means for assessing vehicle damage.

If perforation occurs what are the chances of some level of damage occuring to the vehicle or crew. This is a function of residual velocity, caliber, plate quality, fragmentation, blast, incendiary effects, etc. If I were the god of computer wargames, I'd break the potential damage effects into standard NATO performance criteria.

P(k): probability of a catastrophic kill
P(m) : probability of a mobility kill
P(f): probability of a fire power kill

Best Regards
Jeff
 
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#36
With the proviso of "given the time and budget"...

The behind-armor effects need moderately detailed modelling. There are areas to explore (dependent on the state of the round/frag post-perforation) including damage to crew and key components, the possibilities of fires in engine, fuel, AP storeage and HE storage. I'd rather pick on some of the key components than on a simple "firepower" kill, for instance.

On the downrange velocity and angle of incidence - that is all quite possible. We calc the downrange v already. AoI gets a little more complex, but is doable.

It is a good point to break the incoming rounds up by class. Very neat solution so that we don't need one madly-all-encompassing algorithm. But, being dense - what is "HHA"? And dividing into round classes would indeed make it simpler to add post-war projectiles, HVAP, Long Rods blah blah :)
 
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#37
Hi Alan:

Budget is of course always a problem :D But than some of us are more interested in the principal of the thing rather than actual amounts :D

HHA is High Hardness Armor (or homogeneous hard armor [UK designation] or hard homogeneous armor [USA designation] -- I have seen it expressed in a number of ways). Thin sections are very effective against under-matching (t/d >1) and matching (t/d=1) small caliber AP and of course common ball. Thick sections are very effective against under-matching AP projectiles. The defeat mechanism is typically nose shatter or lowering of the critical ricochet angle. Moreover, assuming the plate doesn't buckel under the impact of say a very low t/d event, than critical ricochet angle is directly related to target hardness, obliquity and impact velocity. HHA plates were also found to have a lower propensity toward buckling under ballistic attack from matching and overmatching projectiles -- I mean catastrophic plate buckling -- for tanks and other AFVs that employed very high obliquity plate configurations.

It was often used in aircraft of the period, as well as armored cars, halftracks and such as its weight efficiency relative to small caliber threats was much better than RHA. It was also used on the Soviet T-34 and proved to be very effective against 1941
 
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#39
[RO]Wilsonam said:
Aha - hence the very high BHN in thinner Soviet armours of the period? Just never heard a specific acronym for it before... thanks!
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Yes -- independent metallurgical testing conducted by both Aberdeen as well as Shoeburyness during the war on armor steel samples extracted from "lend lease" T-34s indicate it employed homogenous hard armor plate. German ballistic test documents I have from the war also indicate armor employed on captured T-34s had a particularly high hardness level.

There has also been some indications by various grognards on the subject that high hardness cast armor was used in the IS-2 (high hard cast hulls and cast turrets) and the T34 (high hard cast turrets). However, I personally have not as yet seen any metallurgical reports from the period that verifies this latter bit.

Cast armor of moderate quality is about the equivelent thickness of ~0.85 to ~0.95 of RHA -- depending upon t/d. High Hardness Cast would be at a serious disadvantage against matching and over matching projectile attacks. This would imply the sides and rear of an IS-2 (turret and Hull) would really be at a disadvantage against 75mm and 88mm pzgr. As I recall there were some combat reports (see Jentz Panzertruppen) indicating Hetzers could punch holes in the sides of an IS-2 at about 1000meters or some such thing. Course combat reports are always tricky to rely upon given the number of potential variables involved in such things. Vehicle cant at the moment of impact -- range estimation errors -- sloping ground -- location of hit -- all can play havoc with any sort of rigerous interpretation of combat reports and armor penetration capability.
 
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