Elongation of Homogeneous Armor

[Bgile]

This is a very recent post by Nathan Okun on a navweaps forum:

http://warships1discussionboards.yuku.c ... 13?page=28

[Dave Saxton]

The link doesn't work.

[Bgile]

It works fine for me.

It's on pg28 of the Battleship combat/Bismarck v KGV thread. It isn't over yet, someone is posting more info.

[Dave Saxton]

Okay I was able to open only the last page, but I see the discussion on that page is about the methodology of measuring elongation. Using the German methods what yields 20% elongation, would be 25% elongation using the US/British methods. Another factor is that elongation is dynamic depending on the hardness and tensile strength of the material. Thus German homogenous armour at 250 brinel and 90kg/mm2 tensile would have elongation =25% (measured using the US method). Thus Wh had = elongation at 90kg/mm2, as STS does at 80kg/mm2. The British tests that showed Wh more resistant to penetration than the British NC armour make more sense in that light. But another factor with that is the fact that un-capped shells are significantly less effective at penetrating homogenous armour than capped shells of equal weight if the homogenous armour's tensile strength exceeds 80kg/mm2.

[Thorsten Wahl]

My name at navweaps is Thoddy.
in my eyes it is necessary to clarify technical meanings, before a certain discussion on the material properties get started.
The "elongation problem" is central part of any discussion on german armor properties, as it has been used to assume some inferiority.

[Bgile]

My name at navweaps is Thoddy.
in my eyes it is necessary to clarify technical meanings, before a certain discussion on the material properties get started.
The "elongation problem" is central part of any discussion on german armor properties, as it has been used to assume some inferiority.

I was assuming that was you. :)

[Thorsten Wahl]

main link to warships-forum
http://warships1discussionboards.yuku.com/

or indirekt via
http://www.navweaps.com/
there is a link "Discussion Boards"

[Thorsten Wahl]

according this piece the ballistic properties were nearly the same. w.z.B.w.

[Thorsten Wahl]

Armour technical meeting 20 th november 1947

british measurments of german 4 1/2" N.C. plates
plate No 37363 (Good plate)
Mechanical testing
50% Proof stress ton/in²-35.6
Maximum stress ton/in²- 47.7
Elongation % -28.6 long
Reduction of Area %- 67.6
plate limit 1100 ft/s at 65 deg against 15" Mark XVIIB
comparative value for british plate not mentiuoned

plate No 29795 (poor plate)
Mechanical testing
50% Proof stress ton/in²-42.6
Maximum stress ton/in²- 51.8
Elongation % -26.6 long; 25.9 trans
Reduction of Area %- 64.9
at 1.100 ft/s plate broken

The striking thing is that that the mechanical properties of the poor plate appears to be superior to the good plate

3 1/4" N.C. plates (plates 33084 , 33085)
plate No 37363 (Good plate)
Mechanical testing
50% Proof stress ton/in²-38.5
Maximum stress ton/in²-51.5
Elongation % -26.3 long; 23,6 trans
Reduction of Area % - 67.3
plate limit 1475 ft/s at 60deg vs 8" S.A.P. Mark IVB
(

plates 33084 and 33085 has proved superior to plates of British manufacture, There appears to be no real significant differences to account for the good performance of the german plates in relation to our own)

)
british average plate limit for same thickness 1380 ft/s

japanese N.C. plate 3.103 "
no mechanical testing
plate limit 1330 ft/s at 60deg vs 8" S.A.P. Mark IVB

Whilst this result is not so high as the standard or equal to the general run on our own plate it is not an unreasonable figure

slightly thinner japanese plates(~2,78") hat some 200 ft/s lower limits(-13%) than standard british plates

[delcyros]

As to plate No 37363 (Good plate) vs plate No 29795 (poor plate). I observe that both, elongation and reduction of area is lower on the 2nd example, thus at higher obliquity and against a 15in sized projectile I would expect the 2nd plate to be more easy to fail by fracture than the 1st one. The mechanical properties are not entriely in disagreement to the result.

The thickness of the 2nd batch to be tested was 3.141in (=80mm Wh), do we have information about thinner plates, too? Particularely in the 40-60mm thickness range. There is some evidence to suggest that there was a different treatment for 80-100mm plates, requiring somehow harder surfaces than for Wh thinner plates.

On the other hand, this result is impossible to resim with M79APCLC. It would require a naval limit velocity of 1997 fps rather than 1475fps. Implying either a much weaker plate quality (Q=0.67 instead of Q=1.0) or a much stronger projectile than the reference one.

[Dave Saxton]

Ductility is only one factor in armour quality, but some of these modern programs seem to be making it the primary indicator of quality. The second plate has higher tensile and yield- meaning it's harder-about 225-230 brinell. The elongation being 26.6% is actually outstanding for that level of hardness-actually above standard. The ballistic performance relative to the first plate can be explained by the fact that they were attacked with capped heavy shell. Harder and stronger homogenous plates do somewhat poorer against heavy capped shell during oblique impact according to Krupp, but they consistantly do better against uncapped or de-capped heavy shell if the tensile is greater than 80kg/mm2. This is why the resistance plate should be harder in a spaced array but be limited in hardness in single plate system.

Tensile strength and yield strength also important factors for ballistic resistance.

The hardness of the plates could be treated to whatever level of brinel hardness and therefore tensile strength which was deemed necessary for the specific application, as long as it wasn't more than about 6"-7"thick. Generally the thinner plates, could be treated to higher levels of hardness than the thicker plates while still retaining a minimum acceptable ductility at the max acceptable hardness of the given thickness range. If homogenous armour is thicker than 15cm it becomes difficult to treat evenly, because the middle of the thick plate doesn't cool properly. This is an untractable problem of thick homogenous armour.

[RobertsonN]

Could overhardness in an AON scheme explain the apparent poor performance of French NC armor at oblique impact to large capped shells? The example I am thinking of is Dunkerque against the Hood. At about 15500 yds at Oran in 1940 a British 15 in shell perforated the Dunkerque's 4.5 in NC deck travelling some way beyond before detonating and causing much damage, e.g. the main fire control was knocked out due to power loss. The generally accepted value for the horizontal penetration of the British 15 in gun was only a little over 2 in at this range. As the ship was in harbor it should have been on an even keel and there seems little doubt about the range as another 15 in shell ricochetted off the roof of one of the main battery turrets at about the same time. The performance of the French NC armor also seemed below par in Jean Bart at Casablanca, but not as bad as in the case of the Dunkerque.

[Dave Saxton]

On the other hand, this result is impossible to resim with M79APCLC. It would require a naval limit velocity of 1997 fps rather than 1475fps. Implying either a much weaker plate quality (Q=0.67 instead of Q=1.0) or a much stronger projectile than the reference one.

Note from the Doc that the British standard BL for their own armour (8" SAP IVB @60*) is 1380 F/s and in the previously posted Doc, their NC armour BL of the same thickness was an average of 1351 F/s from tests for the same shell and striking angle.

[Dave Saxton]

Could overhardness in an AON scheme explain the apparent poor performance of French NC armor at oblique impact to large capped shells? The example I am thinking of is Dunkerque against the Hood. At about 15500 yds at Oran in 1940 a British 15 in shell perforated the Dunkerque's 4.5 in NC deck travelling some way beyond before detonating and causing much damage, e.g. the main fire control was knocked out due to power loss. The generally accepted value for the horizontal penetration of the British 15 in gun was only a little over 2 in at this range. As the ship was in harbor it should have been on an even keel and there seems little doubt about the range as another 15 in shell ricochetted off the roof of one of the main battery turrets at about the same time. The performance of the French NC armor also seemed below par in Jean Bart at Casablanca, but not as bad as in the case of the Dunkerque.

I thought the Dunkerque penetration was through the belt, or is this a different penetration?

The JB's poor performance vs capped shell indicates poor quality deck armour. Was it overhard? I don't know? I do know that the French armour quality was considered very poor by German engineers. I have also found indications that the NC French armour was degraded by sulfer inclusions, which would have made it brittle.

[RobertsonN]

Thanks for this information, which is new to me. The account of the action by Dulin and Garzke which gives considerable detail of this hit says the shell penetrated the deck. I agree though that this seems scarcely possible at 15500 yds and that a penetration through the belt is more plausible.
Dulin and Garzke rate these French designs as outstanding. Perhaps they were as designs, but a perusal of the damage that was caused to them by shells, a non-contact torpedo and GP bombs indicates that they suffered badly on every occasion they were in action.