Mornin' /k/!

>>34520542
I'd say so, the steel would be too thick to resonate properly when hit, so there'd be no reverberation on the inside.

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>>34520565
Spalling would be the biggest issue but that seems to have been avoided due to the composition and manufacturing methods for metal fortifications.
I'm probably stupid but I have a hard time following all the archaic names for certain types of iron and their method of construction, But I have come down to 3 types of iron that I can say were commonly used in fortification.

In order of most effective to least the 3 types of iron fortification I read about are: Rolled, Hammered, and Cast (Referred to as Chilled iron).
Additionally malleable metals of about 18' proved to be more effective than hard/face-hardened metals measuring 20-23" thick because they wouldn't shatter after repeated hits.

A lot of hate was directed at that bunker.

>>34520542

jesus....

>>34520542
more like a dull "bonk"

>>34520542
>You think they could hear after this?
Hear? Imagine the massive ptsd after this...
Targeted and hit for hours, locked inside a tiny bell, waiting for "the one". I'm almost certain they prayed for being killed promptly at the end.

they wouldnt be alive after spalling

>>34524557
This one's deliberately too soft for spall

>>34520542

i wanna see something hit it in slow motion

it's like a big chunk of chocolate fudge

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>>34524591
I doubt that, it wouldnt be hard enough to stop the projectile in that case. If theres a spall liner, thats another case, though i doubt that too.

There are some good stories from the crew of the Monitor and the Virginia that were blasting away at each other. They said it was maddening.

>>34524625

you'd be wrong. Tank armor is nothing compared to feet of steel.

>>34524727
If it was steel, then it its hard enough to transmit enough energy for spalling to occur on the other side.

Any specs on the thickness of that steel?

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>>34524727
>>34524824
As far as I know all documentation on metal fortifications states they were made out of malleable iron between 8" and 18" thick, It was found that harder metals like steel would shatter after a few artillery hits so they used a softer iron that could absorb the blows..

>>34525001
Well, as that picture shows, iron generally cracks rather easily which makes spalling a reality. Im sure the issue is really the thickness of the armor, and that armor steel is more expensive than its iron counterpart, and thus allowed for thicker and, more importantly cheaper fortification.

Though i could be wrong of course, im by no means an expert.

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I don't really have much metallurgical expertise to contribute, so here's a block of steel that was hit by a ball bearing travelling 6.8 kilometers per second.

>>34525042
>When the .45 acp hits you

>>34521262
Small arms on the hull of a Bradley is very audible, even with ERA, a CVC on, and the engine right next to me.

>>34524625
>Drive Sherman tank as top tier
>Platoon of enemy Pz1C's appear
>"Haha let's see them penetrating my armor"
>3 secs later

https://youtu.be/QfDoQwIAaXg
Some cool slow motion
Shows spalling of small arms on steel.
>>34524619

>>34525161
more like

>drive sherman in detroit
>pull my head out of the gutter for 1 freaking second
>tyrone and his friends steal our tracks
>1 45 hipoint later

>>34520542
I've been in one of these, its a German Sechsschartenturm heavy MG bunker. According to the tour guide, who showed us these photos, none of these hits penetrated.

>>34524824
The one I've visited in the Channel islands was 12in of steel. Impromptu testing of similar captured bunkers on the Normandy coast showed they were basically impenetrable by tank guns.

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>>34525031
General Brialmont did testing of different types of metal for turrets and casemates in land fortification and came to the conclusion that harder metals provided no advantage assuming they didn't perform worse.

>http://chestofbooks.com/crafts/scientific-american/sup4/The-Use-Of-Iron-In-Fortification.html
>The (cast) cupola was broken; but it is to be remarked that a movable and well-covered one would not have been placed under so disadvantageous circumstances as the one under consideration, upon which it was easy to superpose the blows. An endeavor was next made to substitute a tougher metal for casehardened iron, and steel was naturally thought of. But hammered steel broke likewise, and a mixed or compound metal was still less successful. It became necessary, therefore, to reject hard metals, and to have recourse to malleable ones; and the one selected was rolled iron.

>>34525042
Actually I'm pretty sure that is a block of aluminium.

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>>34525042
>ball bearing travelling 6.8 kilometers per second.

>>34521262
you are referring to working processes.
you should see what I need to learn in the collision industry.

>>34525042
>6.8 km/sec
>22,300 fps
Calling bullshit on that one

>>34525317
>>34526971

Allow me to introduce you...

https://en.wikipedia.org/wiki/Light-gas_gun

>Using hydrogen gas and powered by a shotgun shell, it achieves a velocity of 7 km/s.

>>34527022
Currently taking fluid mechanics, interesting shit

>>34525031
Steel is more brittle than iron. Iron is quite soft and so to crack iron takes quite a bit of doing, and is usually the result of a large displacement of metal rather than the severity of the hit. It's partly why the exhaust side of turbochargers are usually made of iron. If the impeller spins fast enough to "burst" (at 90k rpms, the turbo impeller on the exhaust side structurally can't hold together anymore), iron is a much better burst containment than steel since it will be less likely to shatter with a sudden impact. The iron will "catch" the fragments.

http://www.motoiq.com/MagazineArticles/ID/3909/Lessons-in-Turbo-Technology-with-Garrett--Burst-Containment.aspx
For more info.

While sectional density and velocity are king in armor penetration from an armor piercing round's perspective, hardness is also important. Hardness from an armor's perspective does provide additional protection, especially if struck with oblique shots. The harder steel is by definition less ductile than softer steel, and definitely less ductile than iron. This means the round attempting to penetrate has a worse ability to "bite" into the armor.

That's why modern penetrators are made of tungsten alloy or depleted uranium and are sub-caliber sabot rounds. Maximum hardness to bite into oblique facing armor, maximum sectional density to defeat the armor's ability to withstand the inertia at a given cross-section, maximum velocity to multiply the inertia.

>>34525690
>you should see what I need to learn in the collision industry.

is there a crash course?

>>34527309
DAD GET OFF THE FUCKING INTERNET

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>>34520542
god damn...

>>34527309
>is there a crash course?

https://youtu.be/ObpcGNCU944

>>34520542
Cloches had either cast steel armor ~0.2-0.3m thick, or were made of concrete with steel facing. The largest encasements were designed to take direct hits from ~420mm artillery ( Fortress France: The Maginot Line and French Defenses in World War II )

The large steel pieces were likely cast in sections and then face hardened, similar to how naval armor was manufactured during that time period. It's probably either Krupp Cemented, or perhaps similar to what we now call RHA. I cant see them using mild steel, the french went all out on Maginot.

>>34525288
That data was hideous obsolete by even 1930; Here's a pretty good overview of naval armor up through before WWII

> http://www.eugeneleeslover.com/ARMOR-CHAPTER-XII-A.html
And this guy went all out, digging into metallurgical data. Literal wall of text on tier with scientific papers.
> http://www.combinedfleet.com/metalprp.htm

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>>34529668
It may have been obsolete data but quite a lot of of turrets and cloches were reused from older fortifications.

>>34527169
A bigger part of why turbine housings are made of cast iron is ease of casting (casting steel is quite costly) and the growth of the material with temperature (forgot the jargon, quite tired).