Tower with cells: about the armor of the Soviet T-80U tank
Back in 1984, the Soviet Union adopted Army was accepted танк The T-80U, which became the last serial representative of the gas turbine "eighties" family in the USSR. This machine, being the flagship of domestic tank building of those years, absorbed many advanced solutions, including new combined armor of the turret, which included metal-polymer cellular blocks for protection against cumulative ammunition. What they are and how they resist attacking weapons, we will talk about in this material.
About introductory notes
Perhaps we should start with a banality: steel armor, as the only element of a tank's ballistic protection, has long since lost its relevance. It began to become morally obsolete in this regard back in the middle of the last century due to the growth of armor penetration of shells (primarily cumulative), which was becoming increasingly difficult to resist by increasing the thickness of steel arrays, since this led to an exorbitant increase in the mass of the combat vehicle.
These circumstances, as is known, became the reason for the appearance of combined armor, which provided for the use - in addition to metal elements - of various fillers of lower density, which made it possible to ensure the required resistance of the tank to destructive weapons while maintaining the above indicator within reasonable limits.
Of course, in a single combined armor, all its components in one way or another affect both sub-caliber and cumulative ammunition. But this effect is by no means the same due to the fact that kinetic projectiles react rather weakly to low-density obstacles, while cumulative ones are much better. Therefore, certain requirements are imposed on light fillers, since designers are often forced to literally maneuver between them and heavy (the same steel) elements, maintaining some balance in the durability, weight and dimensions of the armor.
Among them: a durability indicator close to that of steel armor of the same thickness, as well as a lower weight than steel. Roughly speaking, if a conditional 100 mm layer of filler is equivalent in durability to a sheet of armor steel 80-90 mm thick and at the same time weighs half as much as this sheet itself, then this is a quite good filler. Very simplified and exaggerated, of course.
The resistance indicator of a material itself is approximately calculated by its overall coefficient. For example, to find out what the steel equivalent of a 100mm layer of N filler having a factor of 1,5 would be, you would divide the 100mm by 1,5. The result is 66 mm steel equivalent.
Passive armor
In Soviet tank building, which professes the rule “against sub-caliber shells - mainly steel, and against cumulative shells - steel and filler,” materials were used for a long time as light fillers that can be classified as passive armor, providing protection from the attacking body solely due to its physical and mechanical properties.
And, perhaps, the most famous of them is fiberglass, consisting of glass fiber bonded with polymer substances. Its density is only about two grams per cubic centimeter, and the overall coefficient against cumulative ammunition in armor barriers of the “steel+textolite+steel” type is approximately 1,6. That is, a conventional 100 millimeters of this material produces about 62 mm in steel equivalent against cumulative jets. If the armor part has a configuration in which several layers of textolite are combined with steel sheets, then the coefficient is about 1,3.
Armor fiberglass is one of the most famous fillers for the armor of Soviet tanks
For its time, it was a pretty good filler, which was used in the frontal parts of the hulls of almost all Soviet T-64, T-72 (with the exception of T-72B) and T-80 tanks. Only its thickness changed and steel sheets were added. He remained on the T-80U.
In the turrets, as the parts of the tank that are most exposed to fire and where there is not much space to go around in terms of dimensions, other components were used. So, for T-64 tanks (from A to BV) it is corundum, which replaced the aluminum used on the early 0,8s. It was a highly hard aluminum-based ceramic with a density of just under four grams per cubic centimeter and provided resistance against cumulative weapons almost identical to steel armor. In other words, its overall coefficient was approximately equal to one (MSTU named after Bauman gives a coefficient of XNUMX).
Model of a tower with corundum filler. All T-64A/B/BV tanks and the first T-80 were equipped with it. 112 mm steel + 138 mm corundum + 138 mm steel with a total dimensions (with inclination angle) of 450 mm. Resistance against cumulative ammunition - 450 mm, against sub-caliber ammunition - 400-410 mm.
However, despite the effectiveness of this filler, the production of cast turrets with it was a great technological challenge, so they were not produced on any tanks other than the T-64 family and the first production T-80. Instead, in the cast turrets of the T-80B/BV and T-72A/AV series tanks, filler was used in the form of rods of non-metallic molding materials, held together before pouring with metal reinforcement, also known as sand rods.
There is no reliable data on the latter, but, most likely, its density differs from corundum to a lesser extent, while its anti-cumulative resistance is much lower. Very approximately, in the overall coefficient - about 1.4.
T-72A turret with sand filling. The total dimensions of the armor are about 530 mm, of which about 120 mm is sand. Durability is approximately equal to 500 mm from cumulative shells, from sub-caliber shells - 400-420 mm. The T-80B and T-80BV turrets were also equipped with similar material with the same durability.
But it’s no secret that progress in “shell manufacturing” also did not stand still - and those requirements for the durability of armor protection for tanks, which were relevant in the 60-70s, could not be relevant in the 80-90s. Therefore, when developing new modifications of vehicles, taking into account the need for increased protection against sub-caliber projectiles (increasing the thickness of steel masses), it was necessary to resort to turret anti-cumulative fillers of a completely different order, more effective and lightweight. We are talking about semi-active armor, using the energy of a cumulative jet to destroy it.
In the T-72B tanks, which were put into service in the same year as the hero of our material, this armor was made of reflective sheets, which were “sandwiches” of steel sheets with a rubber layer between them. And in the T-80U there are polyurethane cellular blocks.
Polyurethane cells
This method of anti-cumulative tank protection was actively proposed by the Institute of Hydrodynamics of the Siberian Branch of the USSR Academy of Sciences back in the 1970s and was based on the fact that a cumulative jet, moving at enormous speed, has practically no strength of its own and can be destroyed (torn) by armor filler enclosed in a small volume.
In other words, if you take a container (cell) that is small in volume and completely closed on all sides with a compressible material placed there, then when a cumulative jet penetrates, a compression shock wave should appear in this very material. Reflecting from the walls of the cell, it causes the filler to move towards the axis of the jet, braking and breaking it due to the collapse of the hole.
Of course, with some conventions.
For example, a cell, in accordance with its shape, must have a certain diameter. If the diameter of the cell is too large, the processes of formation and movement of the shock wave inside it are delayed, causing the destruction of the jet to begin too late. A diameter that is too small reduces the effective mass of the filler. Therefore, the optimal diameter is 10-13% of the penetration capacity of the cumulative jet. As for the thickness of the cell walls, they should be approximately 5-6% of the penetration capacity of the cumulative jet in order to withstand the pressure.
The cell material itself must have not only high wave velocities and low tensile strength, but also good performance characteristics. Because of this, fillers such as concrete or paraffin, which show quite good results in counteracting cumulative jets in cellular armor, have not been used. But I found the most balanced polyester urethane in this regard. It is not prone to brittle fractures in frost; it retains its integrity even after several impacts from projectiles, and it has good adhesion to metals.
The state of the cumulative jet after overcoming an obstacle 13 mm steel + 20 mm cellular layer + 20 mm steel
Moreover, taking into account that the density of polyurethane is literally about 1 gram per cubic centimeter, an armor barrier filled with cells with it will weigh significantly less than a steel plate of the same thickness. Well, you can learn about the durability of such cells from the table below.
Testing of cellular barriers with different cell diameters and wall thicknesses between them. The results of shelling barriers with cumulative ammunition are shown in red. Green – armor penetration of the ammunition against steel armor. Blue – overall coefficient of the cellular barrier. Violet is the average density of the barrier, where the density of polyurethane and metal cell walls is taken into account. In almost all cases it is lower than the density of a solid steel sheet
In fact, the anti-cumulative equivalent of cellular polyurethane armor is identical to steel armor of similar thickness (plus or minus the overall coefficient is 1), and the weight gain compared to solid steel can be up to 60%, as can be seen from the average density of the barrier. These circumstances determined the choice in favor of “cells” as the basis for the anti-cumulative protection of the T-80 modification, which was new at that time.
Of course, there is no more or less accurate information about the form in which the cellular blocks were made for the T-80U. Nevertheless, there are photographs of the filling of the turret of the Ukrainian “Oplot” - it has a similar protection scheme, so the “eighty” most likely has something similar, taking into account the armor schemes circulating on the Internet.
Plates with cellular filler for the Ukrainian “Oplot”
Schematic arrangement of the cellular filler in the T-80U turret
If we talk about protection, then, taking into account the compactness of the cellular filler due to its high overall efficiency, the designers managed to fit them in the niches of the frontal part of the T-80U turret in two rows (closer to the side parts in one row) and supplemented with plates of high-hardness steel at total armor thickness of ±520. Taken together, this entire assembly, taking into account the external and rear armored parts of the turret, produces an equivalent of about 600 mm against cumulative ammunition and about 500 mm against sub-caliber ammunition.
This was quite enough for protection from most sub-caliber and absolutely all cumulative artillery shells of 105 and 120 mm caliber, as well as from most monoblock anti-tank missiles. With the use of built-in dynamic protection, this figure increased to 1000-1100 millimeters for “cumulative” ammunition and 600-625 mm for sub-caliber ammunition, so it is not for nothing that the “ear” is called one of the most armored tanks of the USSR.
Information sources:
"Study of the anti-cumulative resistance of cellular-type armor." Yu.A. Zorov, I.I. Terekhin
“Particular issues of finite ballistics” V.A. Grigoryan, A.N. Beloborodko, N.S. Dorokhov and others.
“Study of the anti-cumulative resistance of cellular-type barriers with inert and active fillers.” A.V. Babkin, S.V. Ladov, S.V. Fedorov.
"Theory and design of the tank", volume 10, book 2.
Information