Brittle Fracture and torpedo resistance

Warship design and construction, terminology, navigation, hydrodynamics, stability, armor schemes, damage control, etc.
Billy
Member
Posts: 21
Joined: Tue Apr 30, 2013 7:00 pm

Brittle Fracture and torpedo resistance

Postby Billy » Fri May 10, 2013 5:10 pm

I found this rather interesting statement in the the book "Introduction to engineering materials" it reads. "Mild steel is ductile at low strain rates at all temperatures above a value of about -170 deg C, but when mild steel is subjected to impact loading conditions the transition from a tough fibrous fracture to a brittle fracture occurs at about 0 deg C. The energy absorbed in fracturing a notched mild steel test piece in a Charpy impact test may reduce from 160 Nm(J) at +15 deg C to about 15 Nm(J) at -5 deg C." It continues with a diagram which is just a straight line slope from one temp to that of the other. It continues,"Failure of parts of mild steel structures by brittle fracture had occurred since steels were first used, but it was only during the 1940s that the problem became highlighted...ships plating.....Certain alloying elements in the steel affect the ductile-brittle transition temperature. the transition temperature is reduced by the presence of manganese and nickel, but is reduced by carbon, nitrogen and phosphorus."

The battleships from Rodney were made from their D-quality steels which had a high manganese content for strength. In tests of her torpedo protection that was designed for resistance against a 750 lb charge, but a full scale section was made and tested against a 1000 lb charge which it resisted. In fact the "thick bulkhead was set in only 3 in and it was thought that it could have resisted a much heavier charge". In fact she was tested by a much larger charge that mimicked very large bombs landing close by that would explode next to the hull, but she also resisted this severe test rather well. Could it be then that the losses suffered by the British of their older Battleships was due to brittle fracture as they too were designed to handle torpedo hits.

The other point of interest was that their was an account of a torpedo piercing the pressure hull of sub and landing in the control room before going off, but giving enough time for a few to escape. There is also evidence of the hull plating been torn outward at torpedo impact sights ie royal oak and other sunken wrecks. There was a calculation that a torpedo would need at least 25 kn to pierce the hull of a ship. The question is what was the details of torpedo fuses and perhaps could a one pierce the hull given a malfunction before going off and how often could these malfunctions take place, or was there any delay involved in the fuse itself? If anyone has any details? :D

User avatar
tommy303
Senior Member
Posts: 1526
Joined: Mon Oct 18, 2004 4:19 pm
Location: Arizona
Contact:

Re: Brittle Fracture and torpedo resistance

Postby tommy303 » Fri May 10, 2013 10:02 pm

Could it be then that the losses suffered by the British of their older Battleships was due to brittle fracture as they too were designed to handle torpedo hits.


It was probably more a question of how much resistance the systems on older vessels were built to withstand. I believe the Royal Oak and her sisters were only built to withstand warheads of about 400 to 500-lbs, even with the external bulges fitted after WW1, but the torpedoes in use in WW2 were rather more powerful.

Generally, the torpedo pistols or fuzes were designed for very quick operation since it was necessary to detonate the warhead before it could deform too much and be rendered inert by impact. There were times when a torpedo would actually penetrate the hull plating of a light vessel before detonation, as described in several damage surveys during the war, but for the most part detonation of the warhead was usually outside of the hull. It is hard to imagine a torpedo physically penetrating the outer hull and the very stout pressure hull of a submarine.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

Byron Angel
Senior Member
Posts: 730
Joined: Sun Mar 06, 2011 1:06 am

Re: Brittle Fracture and torpedo resistance

Postby Byron Angel » Sat May 11, 2013 12:25 pm

It's worth noting that many (most?) of the losses of old British BBs/BCs to underwater attack were suffered in warm waters - the Mediterranean and Pacific (including Renown here).

B

User avatar
tommy303
Senior Member
Posts: 1526
Joined: Mon Oct 18, 2004 4:19 pm
Location: Arizona
Contact:

Re: Brittle Fracture and torpedo resistance

Postby tommy303 » Sat May 11, 2013 9:17 pm

Hi Byron,

I think you meant Repulse, not Renown.

Billy,
There is also evidence of the hull plating been torn outward at torpedo impact sights ie royal oak


This is probably the result of contact detonations on the plating of the outer protective bulge; the generated gas bubble would have blown in the bulge plating, which was added onto the normal hull plating to increase the depth of the protection and been in part reflected back by the normal hull plating before it had completely ruptured.

Their shoulders held the sky suspended;
They stood and Earth's foundations stay;
What God abandoned these defended;
And saved the sum of things for pay.

Byron Angel
Senior Member
Posts: 730
Joined: Sun Mar 06, 2011 1:06 am

Re: Brittle Fracture and torpedo resistance

Postby Byron Angel » Sun May 12, 2013 10:45 pm

tommy303 wrote:Hi Byron,

I think you meant Repulse, not Renown.



..... Yes, indeed. My bad.

B

Billy
Member
Posts: 21
Joined: Tue Apr 30, 2013 7:00 pm

Re: Brittle Fracture and torpedo resistance

Postby Billy » Sat Apr 11, 2015 7:14 pm

Hi there. I sorry I've been away for quite a while. Anyway what I forgot to include was the said article for ductile brittle transition to occur under impact starts at 15 C. Then the strength of the steel declines linearly from 160 Nm all the the way down to 15 Nm at 5 C. So the colder the worse it gets. But would see it implicated from 15 C. Also can't help but wonder at the way German ships seemed to handle multiple torpedo strikes. Ie Scharnhorst that took quite a few, I think it was 5 and could still manage 25 kn. I do not know the composition of the their steel but do know that the British construction steels would have been immune from Rodney on. Also to be considered is the use of aluminized explosives which could massively increase the destructive force of explosives which saw their implementation within and in some cases at the start of WW2.

User avatar
Dave Saxton
Supporter
Posts: 2881
Joined: Sat Nov 27, 2004 9:02 pm
Location: Rocky Mountains USA

Re: Brittle Fracture and torpedo resistance

Postby Dave Saxton » Sun Apr 12, 2015 2:01 pm

The Specification for D steel are:
UTS: 84,000-88,000 psi
YTS: 46,000 psi
Ductility: 17% Elongation in 8-inches.

DW (D weldable used after 1942) had the carbon reduced from 0.26%-0.30% (by weight) to 0.23%
UTS: 70,000 - 80,000 psi
YTS: 44,000 psi
Ductility: 17% elongation in 8-inches.

Also can't help but wonder at the way German ships seemed to handle multiple torpedo strikes..... I do not know the composition of the their steel


The German construction steel was Stahl-52

1942 tests (examining and addressing some weld failures) revealed these mechanical characteristics:
UTS: 53.3 kg/mm2
YTS: 37 kg/mm2
Ductility: 32% elongation, 61% reduction of area.

Welds using E52K low hydrogen electrode was
UTS: 52.7 kg/mm2
YTS: 45.7 kg/mm2
Ductility: Elongation 27.5%

Composition was:
C- 0.14%
Si-0.36%
Mn--1.49%
Cu-0.37%

German torpedo bulkheads were constructed from Ww homogenous armour, a treated chrom/moly steel. Ww was weldable but welding directly to armoured bulkheads was banned until Aug 1939. Therefore, the Scharnhorst and Bismarck classes ..ect.. had their armoured bulkheads riveted. The Ww from Tirpitz tested for this composition:

C-0.22%
Si-0.34%
Cr-2.67%
Ni-0.80%
Mn-0.35%
Mo:-0.47%
Cu-0.11%
Entering a night sea battle is an awesome business.The enveloping darkness, hiding the enemy's.. seems a living thing, malignant and oppressive.Swishing water at the bow and stern mark an inexorable advance toward an unknown destiny.


Return to “Naval Technology”

Who is online

Users browsing this forum: No registered users and 1 guest