Aluminum armor is not concrete, you can't reinforce it
Creating new or improving existing armor tanks and any other combat vehicles is a process that includes both theoretical calculations and practical tests that allow us to evaluate the effectiveness and, relatively speaking, the operability of protective structures in conditions close to real ones. However, not all inventions of armor designers pass this test.
A striking example here is the aluminum armor for light combat vehicles, reinforced from the inside with steel wire, which received a "fail" from Soviet testers. Heavy, difficult to manufacture, and at the same time less durable and resistant than its classic homogeneous aluminum counterpart.
Instead of an introduction
Aluminum armor can rightfully be called, if not revolutionary, then at least a significant achievement in the field of providing protection for combat equipment - and there is, of course, a reason for such flattering epithets. It is that aluminum has opened up wide opportunities for tank builders around the world in the field of creating combat vehicles whose weight is strictly limited - light tanks, airborne combat vehicles, infantry fighting vehicles and armored personnel carriers.
This is not surprising. Aluminum, as well as alloys based on it, have a relatively low density - more than two times less than that of steel. Because of this, aluminum armor, especially at rational angles of inclination, can provide a weight gain of up to 30% or even more compared to steel plates of similar resistance in terms of protection against armor-piercing bullets of small arms. weapons and small-caliber gun shells. So the interest in the "luminescent" is quite understandable - although it will be thicker, it is significantly lighter.
BMD-1 - carrier of armor made of ABT-101 alloy
This is, in general, the reason for the interest of designers in improving aluminum armor and structures based on it in terms of increasing their bullet and projectile resistance while maintaining an acceptable weight. And if we talk about the methods implemented in practice both in our country and abroad, they mainly consisted of developing new alloys (an example is the transition from the bulletproof alloy ABT-101 to the projectile-proof ABT-102 in the USSR) and introducing additional screens into the armor design of vehicles, like the BMP-3 and Bradley.
However, in the past there were, let's say, not quite standard approaches in the form of creating bimetallic plates from high-hardness steel and armored aluminum, welded together by explosion, as well as obtaining reinforced aluminum armor. We already wrote about the first in the material "Bimetallic armor: aluminum and steel in one bottle", and we will focus on the second one today.
Almost like reinforced concrete
Oddly enough, we need to start with reinforced concrete. Everyone probably has at least a minimal idea of what it is. In a very simplified form, reinforced concrete structures, be it slabs, piles and other elements, are concrete reinforced with metal (less often from other materials) reinforcement in the form of rods, meshes or frames that increase the overall strength of the structure. So, reinforced aluminum armor is a similar thing.
The idea is based on the introduction of steel wire meshes or rods into an aluminum alloy armor plate by hot rolling or welding the aluminum layers with the mesh (rods) placed between them into a single whole. In theory, such reinforcement should significantly increase the armor's resistance to destructive means of relatively homogeneous plates with a small increase in weight, since the overlap of the meshes/rods should be provided in such a way that the bullet (or projectile) in any case hits the steel component, having penetrated the outer layer of aluminum.
Now, of course, it is impossible to say which country's engineers were the first to come up with the idea of creating such a composite, however, the USSR was also interested in this topic at least since the late 1970s, because at first glance this technology had prospects. However, even today, among ordinary fans of armored vehicles and even experts, there are now and then similar speculations, like, why haven't they thought of crossing aluminum with steel yet - the BMP and BMD would not be so "full of holes".
Test
However, theory is one thing, and practice is something completely different, so the only thing that can tell us the most about the qualities of the armor is reports on its shelling tests. And, of course, there are some - they were published in Soviet technical literature in 1980 and are no longer classified, so let's move on to familiarizing ourselves with them, but first about the introductory information.
For the tests, plates made of aluminum alloys AD1, D-20, AMG6, V48, K48 and serial bulletproof alloy ABT-10, used for the manufacture of BMD-1, were used. For their reinforcement, wire with a diameter of 0,3 to 5 millimeters made of high-strength stainless steel Kh18N9T and high-carbon steels U8A and U9 were used. Reinforcement with wire with a diameter of up to 1 millimeter was carried out using hot rolling, and with a diameter of more than 1 mm - explosion welding.
Sectional view of aluminum armor reinforced with steel wire (explosive welding)
The armor plates obtained in this way were fired at with armor-piercing bullets of 7,62 mm and 12,7 mm caliber at different angles to simulate the design angles of inclination of the armor of military vehicles, after which their level of resistance and equivalent weight were assessed in comparison with homogeneous plates made of the same alloys.
So, what are the results? After all, let us recall that in theory, reinforcement due to the presence of steel fibers in aluminum should increase the bulletproof (and projectile-proof too) resistance of armor, additionally destroying the attacking body in the thickness of the less dense material.
Here, it is probably worth immediately answering the logical question about the survivability of such armor, which implies the ability of the barrier to maintain protective functions when repeatedly exposed to weapons of destruction. Of course, there were complaints about it, since aluminum plates reinforced with rods tended to delaminate after a small number of hits. However, with high-quality adhesion of steel fibers to the aluminum matrix (a question of production technology), some plates measuring 150x150 mm demonstrated good survivability, withstanding up to 10-12 hits without delamination.
The problems lie elsewhere. The reinforced armor turned out to be heavy, which is understandable, because steel obviously does not reduce mass, but on the contrary. But the difference in weight compared to homogeneous aluminum plates turned out to be significant - in some examples it was 30% or more. For example, a plate of ABT-101 alloy reinforced with ten layers of mesh (made of steel wire), 19,5 mm thick, weighed the same as a homogeneous ABT-101 sheet 26 mm thick.
However, the increased mass is not compensated by the increased durability of the reinforced plates. During the experimental firing, it was found that they have a large anisotropy of properties. In other words, if the plate is hit at an angle along the direction of the wire, the bullet simply shifts it and goes around it, easily penetrating the armor. If the hit occurs at an angle across the wire, the bullet, contacting it, normalizes (changes the trajectory to close to perpendicular to the armor) in the thickness of the armor sheet, which only increases its penetrating ability.
To appreciate how bad things are, take a look at the table below. It shows data on reinforcing aluminum with steel meshes - and, by the way, the situation with rods is about the same.
In the table, it is worth paying attention to the level of resistance (Vпкп), expressed in the maximum speed of conditional defeats - the speed of the bullet at which through holes, breaches, etc. are not formed in the armor. Well, and, of course, the weight of the plates. In all these parameters, reinforced aluminum armor is significantly inferior to homogeneous plates - no increase in resistance, only a useless increase in weight. Moreover, with an increase in the thickness of the reinforced armor, the difference in resistance, as well as in weight, only grows.
So yes, aluminum armor is not concrete, and it cannot be reinforced. However, it cannot be ruled out that the negative experience of creating such armor structures, as well as bimetallic sheets "steel + aluminum", influenced the development of a more "workable" layered aluminum armor (you can read about it here) PAS, which, according to rumors, could be used in the wheeled Boomerangs and tracked Kurganets-25s.
Source:
"The Effect of Reinforcement on Increasing the Durability of Aluminum Armor". N.P. Neverova, B.D. Chukhin, E.V. Shiryaev, et al.
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