New Odermatt equations - where to find ammunition data?

[Voyager]

I noticed there are new Odermatt equations available on his website along with Excel spreadsheets for easy calculations: http://www.longrods.ch/down.php

 

What is very interesting they also cover jacketed penetrators and something like tool for designing optimal 120 mm APFSDS rounds. I'd like to play around with them however I have found one important issue - lack of detailed ammunition data. Without this I cannot get good perforation results and compare them to each other. Could you tell me where to find such data?

 

BTW - what is difference between perforation and penetration terms used by Odermatt [the former] and elsewhere [the latter]? Does it mean perforation - 100% guaranteed penetration, penetration - 80% (Russian standard) or 50% (NATO standard) rounds penetrated RHA plate of given thickness during tests?

Edited January 14, 2012 by Voyager

[Max H]

Perforation: how thick a plate it will make a hole through

Penetration: how deep a hole it will make in a semi-infinite target (i.e. a really big steel block)

[Voyager]

So from practical point of view both terms can be treated identically?

[TTK Ciar]

So from practical point of view both terms can be treated identically?

Not at all. As penetration approaches the back surface of a plate, the plate's resistance to further penetration drops. Thus the perforated thickness will be greater than semi-infinite penetration depth.

Edited January 14, 2012 by TTK Ciar

[Lieste]

Not at all. As penetration approaches the back surface of a plate, the plate's resistance to further penetration drops. Thus the perforated thickness will be greater than semi-infinite penetration depth.

 

 

Hmm, I thought Arrow indicated that the low obliquity impact was deeper into a 'penetration' block than the perforation limit of a plate. Only with higher obliquities (above 60 degrees) did the two values converge. ISTR that this was partly because of inadequate lateral confinement in many 'penetration tests', compared to a larger thin plate oblique perforation test.

 

AIUI There are reflection influences reducing the penetrator's effectiveness as well as the final 'break-out' yielding that you mention, the latter being more dominant at higher obliquities, the former stronger at normal impacts.

[Voyager]

OK, so what is simplest way to recalculate perforation values obtained from Odermatt's spreadsheets to commonly used penetration values?

[DB]

I don't think that there is any easy way to do that - all you can do is have confidence that perforation should occur if the penetration value exceeds the armour thickness by a suitable margin. It's up to you to decide how much "overmatch" guarantees that.

 

Don't forget that perforation might mean "makes a mark on a witness plate" or it might mean "50% of mass of projectile exits back surface of the plate", or some other criterion.

[Voyager]

OK, so perforation value is greater than penetration value and is up to me to decide what difference margin to accept. Maybe I show you one example:

 

- let's use first "Penetrator Perforation Limit on Oblique Targets" spreadsheet because it is most general yet probably less accurate than other spreadsheets

 

- I have chosen projectile with reliable data - say, 3BM-9 round data according to Fofanov's website: in-flight projectile length - 518 mm, penetrator dimensions - 410x36 mm, entire penetrator made with steel, muzzle velocity - 1800 m/s

 

- additionally I assumed its terminal velocity at 2 km is 1600 m/s because this round has very significant velocity drop due to its bad design. Also I assumed penetrator's hardness is 500 BHN and its density is 7.85 g/cm^3, frustum length is 50 mm and its upper base diameter is 6 mm so total penetrator length is 410+50=460 mm w/o tracer element having about 58 mm element length. Target plate is made with RHA steel (density 7.85 g/cm^3, hardness 300 BHN), NATO obliquity angle is set to 0 degrees and 60 degrees.

 

Here you are results:

 

- NATO obliquity angle - 0 degrees: plate thickness - 247 mm, perforation (LOS) - 246,7 mm

- NATO obliquity angle - 60 degrees: plate thickness - 144 mm, perforation (LOS) - 288,2 mm.

 

Penetration data for this round found on Fofanov's website: certified penetration at 2 km: 245 mm at 0 deg., 80 mm at 60 deg. (in terms of defeated plate for 60 deg.), average penetration - 290 mm at 0 deg.

 

 

What do you think? Are my data right?

Edited January 15, 2012 by Voyager

[Guest Jason L]

Hmm, I thought Arrow indicated that the low obliquity impact was deeper into a 'penetration' block than the perforation limit of a plate. Only with higher obliquities (above 60 degrees) did the two values converge. ISTR that this was partly because of inadequate lateral confinement in many 'penetration tests', compared to a larger thin plate oblique perforation test.

 

AIUI There are reflection influences reducing the penetrator's effectiveness as well as the final 'break-out' yielding that you mention, the latter being more dominant at higher obliquities, the former stronger at normal impacts.

 

For perpendicular impacts, the peak pressure is generally observed around the moment of initial impact (ie the dwell phase). For increasingly oblique impacts, the process of biting in appears to lower that initial pressure spike such that the peak pressure is generally reached after the shock reaches the back plate face (at least for "thin" targets). By the time peak pressure is reached the back face is going to start bulging.

 

The effect of hydrodynamic tip yaw and deflection during "break"/"bite" in in is IMO far more influential than either wavedynamic interactions within the armour or even back face deformation with regards to obliquity effects - as you increase angle most of the back face deformation happens somewhat out of the penetrator path, wheras all of the yaw/deflection goes into smearing out the penetrator tip and reducing its ability to actually penetrate into the target. Likewise, the largest wavedynamic interaction you're going to see in infinitely wide but thin plates is the rarefactions coming from the shock reflecting off the back face (which is a free surface), which is bad from the perspective of the armour and is effectively the wavedynamic contribution to back surface bulging.

 

That is to stay the primary defeat for thin targets is dwell and deformation of the front interface. I would think it would require and impressive lack of lateral confinement to result in lower perforation depth given the significance of backface deformation losses for perpendicular/near perpendicular impacts.

Edited January 15, 2012 by Jason L