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On 8/19/2021 at 11:43 AM, AriesV said:

Hello (long time lurker), I was wondering how one would calculate the protection provided against long rods by a highly sloped piece of RHA like that found on most modern MBT hull and turret roofs. To this end I have two basic questions.

 

Is it simply the LOS thickness with no shell normalization?  

https://www.researchgate.net/publication/242632628_THE_PENETRATION_PROCESS_OF_LONG_RODS_INTO_THIN_METALLIC_TARGETS_AT_HIGH_OBLIQUITY

This paper makes the following claim about HHS steel angled at 73-77 degrees:

 

"The Mass efficiency (Ef) of the target plates was calculated from the DOP results related to the baseline performance of the rod at the relevant impact velocity. The reference penetration is 95 mm in an RHA block at normal incidence. Based on that, the DOP data indicate Ef in the range of 1.07 to 1.09. That efficiency is mainly related to the obliquity advantage, described above."

 

Would it be reasonable to estimate that non-HH RHA with a greater angle (80-83 degrees) could replicate this mass efficiency?

 

What angle does RHA need to be to deflect/ricochet/shatter/etc. long rods?

I've seen papers that seem to have different definitions of "ricochet" and different testing setups (which makes interpretation difficult). I was wondering if this forum has reached any conclusion in this area.

 

Hi, welcome to SH AriesV.


IIRC, the equations for estimating performance of long rods against homogeneous armor include a fractional exponent on the inverse cosine of the obliquity.  Long rods normalize into sloped armor significantly, and you can actually see this in some test pictures:

ePgAxLD.jpeg

 

So I would expect a monolithic sloped armor to perform less efficiently than a flat one vs. APFSDS.  A series of spaced, sloped plates might be a different story.

As I understand it, it is very difficult to get APFSDS to ricochet.  Exact angle at which ricochet occurs is a fairly complex question which involves the density and moment of inertia around the long axis of the penetrator as well as the hardness and probably elastic modulus of the armor, rather than just a fixed angle.  As APFSDS penetrators have gotten ever greater aspect ratios and switched from steel to tungsten/uranium, it has become correspondingly harder to make them bounce.

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