I had a private question from Baron Alcyoneus but I don't see any reason why the reply couldn't be posted for everyont to learn from. Besides, not everone might agree with my assessment. This may spark some conversation.
Sean
Baron Alcyoneus wrote:I was rereading your text on the 6061/7075.
How can you determine by looking at the different treatment options for a specific material on Matweb, and decide which would be the best one for armor?
From what you've said:
Yield strength: point at which it will dent
Ultimate yield strength: point at which it will crack/break
Modulus of Elasticity is important too...
I assume that the Rockwell Hardness isn't really a factor here, just a measure of the surface hardness or something.
Glendour took some gauntlets to a heat treater, and said that if they broke he was out of business..., and the guy looked in his books, and said ~"using this recipe, they won't crack, and will be really tough".
So I'm wondering how compare a very similar material to see if it will be nearly identical in strength/toughness, or whether it will be weaker or stronger...
OK. The short answer is look for a higher ultimate tensile strength, higher tensile yield strength, and a higher elongation at break. In this case 7075-T6 = 572MPa, 503MPa & 11% while 6061-T6 = 310MPa, 276MPa and 12%. 7075 is going to win hands down. It blows the 6061 out of the water to the same level that ‘spring steel’ outperforms mild steel.
Answering why is a little more then ‘off the cuff’. We have to define a few terms and what they mean mathematically. Let’s look at 2 materials.
6061-T6
http://www.matweb.com/search/DataSheet. ... 7d9e10be5b
and 7075-T6
http://www.matweb.com/search/DataSheet. ... 3f79c51b7d
There are a few criteria on which materials are rated. The most important ones for us are: Hardness, Ultimate Tensile Strength, Tensile yield strength, Elongation at break, and Modulus of Elasticity. In very different materials we also might pay attention to poisons ratio.
Lets assume we are talking about flat lamellar plates of equal sizes. If I bend one in a vice (or by hitting the center up against someone’s soft padding) then it wants to bend. When it bends, one side of the plate stretches and the other side compresses. When we let go the stretched side pulls back and the compressed side pushes forward and the plate returns mostly to shape. The amount of stretch that can happen on one side of the plate before it stops returning to flat is the “Tensile Yield Strengthâ€