# Looking for a book about the De Marre equation



## Thor_Hammerschlag (Oct 15, 2013)

Hello there,

im looking for a book which has information about the DeMarre equation..
This equation was used to determine armor penetration values (based on diameter velocity ..) , for example by the Soviets during the 2nd world war according to WW2 Ballistics Armor and Gunnery.

I tried around a bit and found out that this equation does indeed explain soviet pen data. If anybody is interested in the subject - I can explain it.



Best Regards and thanks in advance


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## mikewint (Oct 16, 2013)

First of all the probiblity of the round hitting is worked out, if it does the angle between the surface and the incoming round is calculated, then you could use the De Marre formula which is 
(velocity ^2 * Mass * (cosine angle) ^(2/n))/ diameter ^3 = C(thickness of plate/diameter of shell)^n where n and C are constants.
However for sub caliber rounds at high angles +30 degrees the n in the (2/n) part of the equation is reduced to 1.11, the represent s the tendancies of these round to break up at steep angles. This was a change that was added in the most recent patch as certain people had noticed the penetration of sub claiber rounds was too high at extream angles.
Now to use the equation you will need the values for constants. You can use the German 75 L48 as a base on which all rounds are standardised. In which case the value for C is 4.25 approximatly.
The value for n is around 1.4-1.5 the higher value the flatter the nose is. For APDS the values are 5.6 for C and 1.37 for n reducing to 1.11 for angles greater than 30 degrees.
BTW this is only how I would do it and it can get alot more complicated.
There are some other factors smaller shells can be destroyed by larger plates that simply will not move out of the way even though the penetration should be greater than the plates thickness, this is the so called shatter gap. Also the t/d ratio can have an effect on this process.


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## Thor_Hammerschlag (Oct 16, 2013)

Hi mike,

im currently using this De Marre equation 








The text under it says that values for the constant K are for usual AP rounds between 2000 and 2500, for APCR rounds between 1400 1800. Source is Franz Kosars "Panzerabwehrkanonen 1916-1977".


I dont really understand that there are several DeMarre equations around .. this is also a reason why im looking for literature.


Back to the equation i found in the book. Its high likely, that it was used to calculate these tables here.
OVERLORD'S BLOG: [WoT] Digging Through Archives: Some Penetration Tests

Notice on the 2nd table on the top - K=2400. It says "The thickness of penetrated armor in mm with K=2400 under 60 degrees with various distances in meters".

I put it in an excel table and it gave me very reasonable results. But only for 0m. There has to be some kind of equation for the velocity as function of the distance in meters - v(m). 

What equations do you know to calculate that?


Regards and thanks


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