Tirpitz plate results...

[marty1]

Looks like George has abandoned ship on this thread

Dave:

Speaking of heat effects -- what is your opinion on the potential for magazine fires to effect ballistic quality of an armor plate? Would the heat from such an event be sufficient to effect armor steels micro-structure in any appreciable way? Or would the heat from this sort of event be insufficient to effect ballistic quality in any appreciable way?

[Dave Saxton]

I don't know for certain what the tempature of the plates would become during a magazine fire. However, the critical transition tempatures for armour plates are not that high. I calculated using a computor program, that a material like Ww would have a martensite start temp, of only about 270* C, and martensite finish temp of about 150*C. KC would have higher transition temps than Wotan, because it would have higher carbon and nickel eqivilancies. Higher transition temps are also true of high nickel content homogenious materials such as AOD or NCA. Lower critical temps of Wotan type materials may help with welding, because the preheat and interpass temps required (to avoid sub critcal temp heating and quenching) would fall short of the tempature ranges were chromium induced grain size grain growth becomes a problem, and the range were chromium carbide precipitation (aka.. Sigma phase) occurs. However, this makes Wotan a rather tempermental material during normal cutting and welding, if the interpass heat, and overall heating and cooling schedules are not respected. One wonders how, and if, many of these potential problems occured on the Gneisenau during it's magazine fire? Did this influance the decisions to rebuild the forward section totally, and the eventual write off?

[marty1]

Thanks Dave. Great explanation.

By the way I have read your post on the books and references section of the forum regarding properties of German armor steel. I have been meaning to put something togeather in response that details similar properties for American Armor steel of the period. I just have not had the time. Have a look there occassionally when the opportunity arises as I do want to get back to that subject in the next week or so.

[delcyros]

Excuse me for unearthing this rather old topic.

Cross country armour trials are really hard to come across. This particulare one stroke me for the ability to cross check it with Facehd version 6.8 for accuracy. I suppose that the projectile used in these trials have been the non-cardonald, standart 15in Mk17b APC (1938 lbs total with 1705lbs body weight).

I was particularely interested to see that the armour plates of former KM TIRPITZ is measured with 12.172in and tested against british CA plates of 520lbs from two different manufacturers, representing standart british CA armour of this period. Please note that 520lbs are 13.0in and not 12.172in!

The following graphs summarizes the trial results:



As can be seen, the E.S.C. plate performed markedly better than the Firth-Brown manufactured plate. Similarely, the large sample plate from TIRPITZ performed surprisingly inferior to the smaller samples, despite the latter are likely to suffer additionally from plate edges effects.

Thus the original comparison compared the poorer performing TIRPITZ plate with the better performing ESC plate. Additionally, little attention was paid to the fact that the ESC plate is approximately 6.8% thicker than the TIRPITZ plate.

Finally, the current version of facehd 6.8 is predicting nearly accurate estimates for the british CA plates (overstating their average performance by ca. 2%) but fails to deliver accurate calculation for the german KC plates. They underestimate their performance compared to the average of the trials by up to 8.3% and I am at a loss to explain this difference.
It´s particularely obvious if You compare the prediction for intact and effective penetration of the mk17b striking 12.172in KC/n.A. at 30 deg obliquity. Facehd requires 1,394fps for full penetration and 1310fps for holing limit (creating an at least calibre sized hole in the plate) while one of the smaller 12.172in plates from TIRPITZ stopped a 15in impacting with 1507fps and 30deg. In the last and admittantly most extreme case, we are dealing with ca. 200fps or 15% difference.

I am curious, any ideas?

[Mostlyharmless]

.....
I was particularely interested to see that the armour plates of former KM TIRPITZ is measured with 12.172in and tested against british CA plates of 520lbs from two different manufacturers, representing standart british CA armour of this period. Please note that 520lbs are 13.0in and not 12.172in!
than the TIRPITZ plate.
......

I suspect that this is the confusion caused by the British measuring thickness of armour using the estimate that 40 pound plates are 1 inch thick. There was an earlier thread on this viewtopic.php?f=13&t=1643 and using the value given there a 520 lb plate should be 12.74 real inches thick.

[dunmunro]

http://www.panzer-war.com/Naab/Tripitz2.jpg

and

[delcyros]

@ mostlyharmless:

thanks. I think this deletes the differences in Facehd v. 6.8 and penetration of british CA.

In the case of the TIRPITZ plates the things are different. 12.172" correspond to either a 486.88lbs (1"=40lbs) plate or 496,617lbs (using 1"=40.8lbs). This convinces me that 12.172in is indeed a precise measurement (probably to avoid the usage of lbs which would be unfit because of fractions for the plate under consideration) and not a miscalculation. A drop from nominal 12.6in to 12.2in was just tolerable in german plate acceptance procedures.
It´s also important because it helps explaining the relative performance between Plate No.27885 and the small samples, which as I believe now, are not 12.172" but 12.5in as those used for trials with 14in APC, mentioned by Dunmunro above.

[delcyros]

Dear Dunmunro,

thanks to You for pointing me to these valuable cross country trials. I have compiled them in the chart below and would have put the perforartion limit exactly where the RN investigators put it, at 1370fps:



Additionally, I have marked the plate extensions and the approximate impact position and plate damage as given in these trials. It can be seen that these plates were hit roughly centered on with the distance between plate edge and projectile about 1.3 to 1.4 cal.

These trials conducted with 14in APC ammunition showed markedly superior penetrative performance than those with 15in APC. Compare the hit with 15in on 520lbs Firth& Brown plate No. 5020, which required only 1389fps for penetration (0.85 cal plate thickness for the 15in) and that of Beardmore´s "C" 480lbs plate No. 6914, which required 1439fps (0.84cal plate thickness for the 14in). Even more pronounced are the differences in action of probably similar 12.5in thick small plate samples to impact: The 14in APC round No. 5899 penetrated in whole condition at 1396 fps while the 15in APC Mk17b was completely stopped by a small sample scale 12.5in plate at 1507fps and just penetrated (broken) at 1539fps.

The reasons for this which I can think of are:

[A] the 14in APC was a significantly better penetrator than the 15in APC mk 17b
the armour tested at was subpar in performance to the plates tested with 15in APC
[C] british 480lbs armour was more efficient in stopping power than 520lbs armour

The sample condition in my mind has a lot to do with these results. Plate edge effects cut into armour piercing performance unless the impact is further away from the plate edge than 3 cal distance. This is evidenced by the british E.S.C. plate in a trial against the 15in Mk17b, which penetrated at 1377fps close to the lower edge and by another impact on the same E.S.C. plate at 1463fps - which was completely stopped by the plate (no plate edge effects). The trial with the 15in APC against the 12.172in TIRPITZ plate No. 27885, which penetrated at 1507 fps and broke away the top edge is also noteworthy for beeing to close to the plate edge.


These small sample impacts from 14in and 15in trials however, always are subject to plate edge effects with the projectile beeing no more than 1.43cal distant to the plate edge. Damage to the face in hit No.5399 for example reaches out to the edge and the failure mode (plate breaking instad of hole formation) is typical for plate edge effects rapidly changing the failuremode of the plate.
The question remains why the equally small samples from the 15in APC impacts didn´t showed this failure. It would be important to know more about the details of plate damage from these trials.

[Thorsten Wahl]

The statement that british armour was "definitely superior to german armor" was replaced in 1948 by a smother formulation " british armor was probably better" with reference to these tests in 1946. ADM 281/127 ARMOUR TECHNICAL COMMITTEE Meeting 22th July 1948

Even the pieces were flamecutted from the armor produced in 1938-40 the pieces are showing a slightly better better performance, than average british armor of 1946.
its obvious that such a comparison also negates any improvement on ballistic porperties of german armor during 1938/39 - 1944/45
additional the pieces were compared with the best performing british plate of the time to show somewhat inferiority.

"the standard of attack for penetration of 480 lbs C plates for 15" Mark XVIIB/30°/1320 Fs"
"the standard of attack for pentration of 15" (600lbs) C plates viz 15" Mark VIIB/30°/1560 Fs"
ADM 28/126 ARMOUR TECHNICAL COMMITTEE Meeting 20 th November 1947

[delcyros]

It´s still a remarkable performance - 0.98 cal penetration* CA at 30 deg obliquity and 476 m/s.
Similar performance of the 38cm L4.4 APC was 0.9 cal KC at 30 deg and 500 m/s (altough the definition here was different requiring the projectile to either completely penetrate in a broken condition or to embedd in the plate halfway through in intact condition, both beeing "grenz").

*) required a hole to e formed in the plate from face to back. The size of the hole was irrelevant.

I would be highly interested to see trials with british, ca. ww2 period shells (both, 14in and 15in) versus british, ca. ww2 period CA.

[Thorsten Wahl]

ADM 281/40 Comparative performance of old (Rodney 1923) armour with modern (1946) armour

Rodneyarmor.jpg (45.33 KiB) Viewed 5945 times

[Thorsten Wahl]

It´s still a remarkable performance - 0.98 cal penetration* CA at 30 deg obliquity and 476 m/s.
Similar performance of the 38cm L4.4 APC was 0.9 cal KC at 30 deg and 500 m/s (altough the definition here was different requiring the projectile to either completely penetrate in a broken condition or to embedd in the plate halfway through in intact condition, both beeing "grenz").

interestingly both projectiles are needing ~100 MJ to achieve an Grenzschuss or penetration against 15 inch plate at 30degrees incidence, if we take both definition as being equal with the british pentration being somwhat lesser as a Grenzschuss.

[delcyros]

Thanks Thorsten.

From these data it appears that british CA as used in comparative trials against TIRPITZ plates is significantly superior to average british CA.
Average british ww2 period CA appears to be slightly inferior to average KC/n.A.of the same period for 420lbs and 520lbs plates, at least.
Very good and very poor plate appear to exist on both sides.

[Thorsten Wahl]

Nathan Okun has postet some data for the 14 " Mark 16 mod 4 projectile
http://www.navweaps.com/index_nathan/Ar ... d-4_AP.pdf

even its definately not easy to derive an angular performance from this data but it's possible to obtain some interesting informations

<M>7596 12.32" 25° 1462 fs CP-E Barely over limit
<M>7016 12.32" 25° 1485 fs IP-E Plate holed

<C>EE90 12.56" 30° 1615fs IP-NBi
<B>2A642A1 12.5" 31° 1625fs IP-NBe
<B>4A712A1 12.46" 31° 1586fs IP-NBe
<B>2B160A1 12.46" 30° 1595fs IP-NBe Plate holed
<M>6711 12.25" 30° 1585fs IP-NBe
<M>7596 12.18" 30° 1573fs IP-NBe Plate holed
<M>6704 12.18" 30.5° 1578 fs IP-NBi
<B>1B134A1 12.18" 30° 1563 fs IP-NBe Plate holed
if I take this data which covers only an area of 5 degrees the general performance seem very similar to KC nA vs german 38cm APshell of same thickness
the resulting pentrationcurve runs parallel in this area to the german data obtained from GKDos 100.
potential differencies in plate quality neglected

but for
thick plate
<B>8915 17.3" 15° 1820fs CP-BFe Barbette plate; barely over NBL
Ditto 17.43" 15° 1710fs IP-E

<B>1B385A1 17.36" 29.5° 2102fs IP-NUe
<M>6741 16.93" 29.5° 2068fs CP-NR Retest plate for lot with 6727 above; no test again
Ditto 17.23" 29.5° 2086fs IP-NBe Passed
<B>4A288A1 17.08" 29.5° 2052fs CP-NBi Barbette plate; low NBL
<B>4A279A1 17.08" 30.x° 2085fs IP-NBi Retest plate for lot with 4A288A1 above; passed
Ditto 17.08" 30.x° 2119fs CP-B2i
the resulting curve shows a loss in relative plateperformance compared to the GkDos 100 data
and this loss seem to be greater for oblique impact.
Additional the curvature of barbetteplate has to be taken into consideration wich offers somwhat better protection as a flat plate of same thickness.

At least one question arose from this data.
Is this loss related to modellimitations of the german pentration model?
Does US plate behave inferior for thick plates?
Does the performance of the german shell drops for thick plate compared to the US shell?

[RobertsonN]

What can be said about traditional IZs from the existence of plate edge effects? Presumably, immunity was calculated for the resistance some distance away from the edge of the plate. Large plates would seem advantageous, assuming constant armor quality with increasing plate size.

Incidentally, I was in the German Technical Museum in Munich at the weekend. There, there are three Krupp plates from 1905: all 70 mm thick, one compound armor, one nickel steel and one hardened nickel steel. 75 mm shells have been fired into them all at about normal. The hardened nickel steel plate was best, resisting a 75 mm shell with a striking velocity of 640 m/s. Much damage to front of plate with steel laminated away, the shell's nose probably right through, but the plate has deformed plastically with a big bulge at the back but no cracks or flaking away of material. The soft nickel plate was penetrable at a little over 400 m/s but with less lamination/flaking type damage at the front of the plate. I thought of M79.

There is also part of one of the diesels that were scheduled for the H-class battleships there: a piston, connecting rod, big end, and cut-off section of the crankshaft.