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Ben P.




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PostPosted: Fri 27 Nov, 2009 1:55 pm    Post subject: Metal Fatigue and Armour         Reply with quote

I would think that metal fatigue would be a problem for armour (considering all the hits it would take in its lifetime)

Right?

Can anyone help me?

-Thanks
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Blaz Berlec




Location: Podgorje, Kamnik, Slovenia, Europe
Joined: 26 Aug 2003
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PostPosted: Fri 27 Nov, 2009 2:19 pm    Post subject:         Reply with quote

Well, just exposure to the force isn't enough to cause the metal fatigue. If there is no deformation to the armour parts (or only elastical deformation occurs), then you don't have to worry, steel doesn't fatigue all that easy (unlike aluminium and it's compounds). But if there is any plastical (permanent) deformation in each event, then you can be sure the bent part will fail eventually.

This can happen due to "all the hits", but they are usually not that repetitive. But some exposed part could take damage by this process (like hinge for gauntlet thumb...). I can also imagine metal fatigue could be a problem if armour isn't designed properly, so it deforms when used (improperly placed pivot rivets, poorly matching shapes...). That could cause repetitive stress on an armour part which would weaken it to the point of failure eventually.


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P. Cha




PostPosted: Fri 27 Nov, 2009 11:11 pm    Post subject:         Reply with quote

Lifetime of the armor...yeah it can...after all a few generation of wars and alterations can cause some issues...lifetime of the original user...probably not. Assuming proper construction of course.
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Daniel Sullivan




Location: California
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PostPosted: Sat 28 Nov, 2009 1:29 pm    Post subject:         Reply with quote

Ben,

Failure from metal fatigue is something that happens over a long period of time vs. a failure due to a blow. It results from a constant stress (i.e. a heavily loaded beam), or a cyclic loading such as constant bending and flexing.

As armor was designed for ease of movement, the hinges, leather straps and sliding rivets would largely eliminate this flexing and bending. Of course rivets and strapping would fail over a period of time, but this could be attributed to "normal" wear and tear. If you were one of the big bucks guy your armor was attended to by some talented fellow to take care of these things before they became a problem.

The exceptions being, cases of very poorly designed armor or an ill fitting battle field pick up. Another case might be when repeated repairs were made to the same piece.

Regards,
Dan
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Colt Reeves





Joined: 09 Mar 2009

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PostPosted: Sat 28 Nov, 2009 2:11 pm    Post subject:         Reply with quote

Not that I'm any expert on this, but I'm thinking of jousting and tourney armor here. All manner of accounts of dented helms and what-have-you. Since metal fatigue is, as everyone has been saying, repetive stress as an object is bent and rebent, this fits the bill nicely. I'm thinking wartime armor might never get a scratch if you're on the winning side (ideally your armor gets hit when things are going wrong), but in "play" you'd be more likely to get things stoved in. This of course all depends on the assumption that dented tourney armor was hammered back into shape and reused consistantly and that war was actually fairly rare and slow-paced for our given pieces of armor... Always exceptions.
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Jared Smith




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PostPosted: Sat 28 Nov, 2009 8:39 pm    Post subject:         Reply with quote

Colt Reeves wrote:
All manner of accounts of dented helms and what-have-you.


It is hard to say how much of the surviving plate exhibited within museums actually saw significant combat. That said, mild steel is a better defense if it deforms upon harsh impact. (Similar to automobile collision principles.) I would guess that wearing out pieces of armour due to real deformation was not just limited to tourney. The accounts of William Marshal included his helm being so badly deformed, while upon his head, that it took a blacksmith to remove it. This happened both in his early life during a melee tourney, and late in his life during a battle within a town. We can say that some specimens of mail and earlier helm pieces (Birka garrison finds, Sutton Hoo, Coppergate helm pieces) appear to have had repeated repairs with substitutions of materials different from overall parent materials, and possible recycling of earlier pieces based upon dimensions of segments.

Absence of evidence is not necessarily evidence of absence!
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Adam Bodorics
Industry Professional




Joined: 15 Apr 2005

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PostPosted: Sun 29 Nov, 2009 9:53 am    Post subject:         Reply with quote

So far I failed to overstress my 1mm mild gauntlets even as I use them quite often to displace attacks, which sometimes results in getting quite hard strikes there. Another harness was repeatedly beaten almost shapeless on the owner to demonstrate protection, no fatigue there either after 4 reshapings. The only case when I did crack a plate was when due to the absence of helpers I couldn't make a straight flute on a huge (over 140cm chest circ.) breastplate and had to rehammer it 8 times.
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