Jane's IDR 2002-07 v.35
Armor for Light Combat Vehicles
Improving the protection of an increasingly important category of vehicle, writes R.M. Ogorkiewicz

The amount of armor light combat vehicles can have has always been constrained by their weight and this has become an increasingly serious problem with the growing reliance of armies on them. Much effort is consequently being devoted to the development of armors that would provide greater ballistic protection with little increase in vehicle weight.
The most direct approach to the problem has been to improve the ballistic properties of steel armor, the traditional armor material of which the turrets and hulls of most light armored vehicles continue to be made. The outcome of this has been the production of high hardness steel armor (HHS), which has been used since the 1960s for many light armored vehicles, from the 3.8-tonne 4x4 Panhard VBL to the new 8x8 Mowag Piranha IV and the 23-tonne Singaporean Bionix 3 tracked infantry fighting vehicle (IFV). HHS has a Brinell hardness (BHN) of around 500 compared with 380 for a typical, standard, rolled homogeneous steel armor (RHA) and is about 20% lighter for a given level of ballistic protection.
So far, relatively limited use has been made of very hard steel armor (VHS) which has a BHN of 600 or more, and offers even greater ballistic protection, as shown in Table 1. Exceptions to this have been the 6x6 Cascavel and Urutu wheeled armored vehicles, of which 2,767 were built in Brazil by the Engesa company during the 1970s and 1980s. In their case, VHS was used as one of the two components of a dual-hardness armor made by roll-bonding two different steels and then heat-treating them to produce plates with a very hard outer layer and a softer but tough backing layer by which the plates could be welded together.
Elsewhere, the use of dual-hardness armor has been inhibited by its cost while that of VHS by itself was limited by the fact that plates of it could not be welded together and had to be attached mechanically to an underlying structure. However, VHS can be very effective as add-on armor and dual-hardness armor is particularly attractive for very light armored vehicles because its hard outer layer is not structurally parasitic, as it is in other two-layered systems, and does not therefore impose structural weight penalties.

Developing aluminum armor
Since the 1950s there has been an alternative to steel armor in the form of aluminum alloys. The pioneering 5083 aluminum-magnesium alloy has been no better in relation to its weight than RHA against armor-piercing (AP) bullets, but it was more efficient structurally and was successfully adopted by the US Army for its M113 tracked armored personnel carrier. Some 74,000 of the M113 and its derivatives were subsequently produced and it remains the most numerous armored vehicle in the western world.
Adoption of the rolled 5083 aluminum armor was followed in the 1960s by the development of heat-treated 7039 aluminum-zincmagnesium alloy, which was superior to it ballistically and was incorporated in a number of US armored vehicles designed at the time. A little later, a similar 7017 alloy was adopted for British vehicles, including the current Warrior IFV. However, alloys of the 7039 type proved susceptible to corrosion stress cracking and delamination. As a result, the current AAV7A1 amphibious assault vehicle of the US Marine Corps (USMC) reverted to the use of the 5083 aluminum armor although its prototypes built in the 1960s used 7039 armor. The quest for aluminum armor that would be at least as good ballistically as the 7039 type but which would not suffer from stress=>

□ Two Panhard VBL scout cars in company with a French Army Leclerc tank. The VBL hull is constructed of high-hardness steel, which is 20% lighter than standard RHA for a given protection level.
□ The low-profile ICV variant of the ST Kinetics Bionix infantry carrier has a baseline structure of HHS, giving protection against 7.62mm AP projectiles and 152mm artillery fragments. The Deisenroth developed applique armor package visible on the glacis can be configured to protect against 14.5mm projectiles and RPG-7 hollow-charge attack.
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=>corrosion problems has led to the development of 2519 alloy armor. This contains less magnesium but a considerably greater amount of copper and has been adopted for the Advanced Amphibious Assault Vehicle (AAAV), which is being developed by General Dynamics Land Systems for the USMC. It promises to be superior to the earlier types of aluminum armor but whether it lives up to expectation will only be known after extensive trials of AAAV prototypes in a sea-water environment.
In any case, ballistically more effective aluminum armor has become less important because of the trend to concentrate its use for the basic structure of combat vehicles, for which aluminum is admirably suited, adding to it outer layers of harder materials which are inherently superior in their resistance to AP bullets. How effective such use of aluminum armor can be has been shown in the UK by the hull of the 13-tonne Alvis Stormer 30 reconnaissance vehicle which weighs only 4 tonnes. It has also been shown in France by the GIAT CHACAL (Char a caisse allegee) program that produced an aluminum hull structure weighing only 3.4 tonnes for a 25- tonne 6x6 IFV. Such low hull weights obviously allow much more of the vehicle weight to be devoted to protection.
The synergistic combination of aluminum armor with outer layers of hard steel has been adopted for a number of recently designed vehicles to provide them with greater protection than that afforded by a single type of armor.
They range from the Fennek light armored reconnaissance vehicle, which is to be produced for the German and Netherlands armies to the Dardo IFV currently in production for the Italian Army. They also include the up-armored, M2A2 of the US Bradley IFV. How good the aluminum-steel combination can be quantified in terms of mass effectiveness (Em), the ratio of the mass of RHA to that of the armor in question providing the same degree of protection against a particular threat. As shown in Table 1, the Em of the combination proves to be greater than that of either HHS or 7039 aluminum by themselves.
Where space allows it, the effectiveness of the aluminum-steel combination can be increased further by separating the two armor layers by an air gap. In the earliest embodiment of this, incorporated in the M113-based Armored Infantry Fighting Vehicle (AIFV) used by several armies and in the original version of the US Bradley IFV, the steel component consists not of one but of two RHA plates only 6mm thick separated from each other and the aluminum armor by air gaps. In this case, the function of the steel plates is to make attacking bullets yaw rather than resist them, and thereby make them strike the aluminum armor less effectively.
A much more effective form of the spaced steel-aluminum armor, at least against AP bullets of up to 14.5mm, was devised in Israel by Rafael and installed on Israeli M113 carriers as well as, later, other armored vehicles. In this case, a single plate of hard steel is perforated by a large number of holes to reduce its weight by about one half and located 250mm in front of the base aluminum armor. The perforated plate tips and the relatively large air gap behind it, as well as damaging attacking bullets, increases their yaw so that they strike the base armor less effectively.
A further refinement of the hard steel-aluminum armor combination was developed in Israel by Urdan Industries and fitted to the sides of the M113 carriers of the Swiss and Danish armies. In it, flat steel plates have been replaced by corrugated plates that introduced obliquity where there was no room for sloping plates, and circular holes have been replaced by narrow elongated holes which helped to reduce the possibility of a bullet hitting the center of a circular hole and therefore not being deflected.

Improved titanium prospects
As an alternative to steel, there is now the possibility of combining aluminum armor with plates of titanium. These have been available since the 1950s and at an early stage=>

Table 1
Armors required to resist 7.62mm x 51 AP bullets at normal impact and point-blank range
Armor material Thickness(mm) Areal density(kg/m2) Em 
Rolled homogeneous steel (380 BHN) 14.5 114 1.00
High-hardness steel (500 BHN) 12.5 98 1.16
Ultra-strong steel 8.5 65 1.75
Dual-hardness steel (face 600 BHN) 8 64 1.78
Aluminum
- 5083 alloy 48 128 0.89
- 7020 alloy 45 125 0.91
- 7039 alloy 38 106 1.08
- 2519 alloy 36 100 1.14
Titanium
6Al-4V alloy 20 89 1.28
Fiber-plastics composite 57 107 1.07
High-hardness steel + 7039 aluminum 20 91 1.25
Alumina + high-hardness steel 12 68 1.68
+ 5083 aluminum 17 52 2.19
+ fiber-plastics 18 49 2.33

□ The hull of the British Army's Warrior ICW is constructed of 7017 aluminum alloy, giving basic protection against 14.5mm attack. With appliqué Chobham side armor packs in place, it has proved it can also protect its crew from 120mm HESH
□ The US Marine Corp's AAV7A1, like the M113, has a baseline structure of 5083 aluminum armor. During the 1990-91 Gulf War this was supplemented by stand-off panels of perforated steel plates designed to increase the yaw of penetrating projectiles, rendering them less effective.
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=>it was found that Ti-6Al-4V titanium-aluminum-vanadium alloy offered greater resistance to bullets in relation to its weight than RHA. However, the very high cost of titanium plates, which were produced to aerospace specifications, prevented them being considered for armored vehicles.
The situation has been changing with the production of titanium alloys to less stringent military specifications and some of them, produced in the US by Allegheny Technologies and by Titanium Metals Corp (TIMET), are claimed to be ballistically as good or even better than standard Ti-6Al-4V alloys while costing 20% less than aerospace quality plate.
At the same time, work carried out by the US Army Research Laboratory in collaboration with the French-German Research Institute Saint Louis has shown that titanium was not only effective against AP bullets but also against the long-rod penetrators of APFSDS projectiles. This is particularly important in view of the increasing use of such projectiles by automatic cannons of calibers as small as 25mm. In fact, against tungsten penetrators titanium has proved to have an Em of 1.6, or in other words to be 60% more effective in relation to its weight than RHA.
The ballistic performance of titanium and the prospect of its cost coming down have encouraged plans for its greater use, particularly as the hard outer layer of softer aluminum armor structures, which is considered the most suitable application for it. A demonstration of its effectiveness in this role is provided by the Mobile Tactical Vehicle Light (MTVL), the stretched version of the M113 carrier produced for the Canadian army. This has been fitted over the front of its hull with titanium plates 50mm and at the sides 32mm thick, which converted it from a vehicle vulnerable to 7.62mm AP to one immune to 14.5mm AP at the cost of an increase in its weight of 1,800kg.
A further indication of the effectiveness of titanium combined with aluminum armor is provided by the decision of the French Army to adopt it, after extensive trials, for its future 8x8 Vehicule Blinde de Combat d'Infanterie (VBCI) as a superior alternative to the combination of ceramics with HHS adopted for other wheeled armored vehicles currently being produced or developed.

Claims for composites
Nobody appears to propose at this stage making complete vehicle hulls from titanium plates. In contrast, there is no lack of suggestions that, in the future, they should be made from fiber-plastics composites, and some experimental vehicle hulls have been successfully made from them. They include the Bradley composite IFV and the Composite Armored Vehicle (CAV) made in the US by United Defense in 1989 and 1997 respectively, and the Advanced Composite Armoured Vehicle Platform (ACAVP) produced in 2000 by what was then the UK Defence Evaluation and Research Agency (DERA) and Vickers Defence Systems.
It has been claimed that the use of fiberplastics composites can produce savings in the weightof combat vehicles of as much as 35%. But such figures are found to apply only to the hulls and not to the weight of complete vehicles, only one third of which is generally contributed by hulls. Moreover, the claims tend to involve the use of ceramics and the 'citadel' design concept of protecting the crew compartment at the expense of the rest of the vehicle, both of which would also make metallic hulls lighter.
So far, as their ballistic performance is concerned, fiber-plastics composites are no better in relation to their weight than RHA, even when they are made with the high strength S-2 glass fibers bonded with an epoxy resin. If hulls made of them are lighter than those of metallic armors it is largely because they can dispense with spall liners. However, the latest type of spall liner has only half the weight of the earlier type of the same thickness made with glass fibers. This type of liner is based on Dyneema ultra-low molecular weight polyethylene fibers made in the Netherlands by DSM, and has been adopted already for the latest version of the German Leopard 2 tank and for XA-188 6x6 armored carriers of the Netherlands Army.
If the savings in the weight of combat vehicles which might be achieved with fiber-plastics composites are not likely to be as high as is sometimes claimed, there is no doubt that their weight can be greatly reduced at a given level of ballistic protection by the use of ceramics. Or, what amounts to the same thing, vehicles of a given weight can be provided by the use of ceramics with considerably greater ballistic protection.

Ceramic-faced armor
Ceramics are ballistically-effective primarily because of their hardness, which is considerably greater than that of other material, and they are also lighter than steel, as shown in Table 2. Their hardness enables them to shatter attacking bullets and the way they fragment themselves when hit spreads the remaining bullet energy over the backing armor making it easier to absorb it.
As show in Table 2, ceramics vary in their hardness. In general, the harder they are the greater is their ability to defeat AP bullets, whose hardness they need to overmatch. Most AP bullets, which have steel cores with a Vickers hardness of 600 to 800 can be overmatched by conventional aluminum oxide (Al2O3) ceramics or alumina. But to defeat AP bullets with tungsten carbide cores, like th 7.62mm FFV developed in Sweden or the=>

Table 2
The density and hardness of typical ceramic and metallic armors
Material Density(kg/m3) Vickers hardness(kg/mm2)
Rolled homogenous steel 7,850 240-380
High-hardness steel 7,850 480-540
Dual-hardness steel, face layer 7,850 600–750
5083 aluminum alloy 2,660 100
7039 aluminum alloy 2,780 150
Titanium, 6Al-4V 4,450 300–370
Soda-lime glass 2,500 450
Aluminum oxide, 85% 3,450 900-970
Aluminum oxide, 95% 3.720 1,150–1,250
Aluminum oxide 99.5% 3,900 1,500–1,700
Aluminum nitride 3,300 1,100
Silicon carbide 3,150 2,200–2,500
Titanium diboride 4,250 2,500–2,700
Boron carbide 2,450 3,000.

□ To avoid stress corrosion, 2519 alloys armor has been adopted for construction of the AAAV, which has also to cope with the potential ill-effects of salt-water corrosion. The structure is overlaid with LIBA Ceramic armor
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=>14.5mm BS 41 fired by Russian KPVT machine guns which have a Vickers hardness of about 1,200 requires ceramics, such as very high purity alumina or silicon carbide. Experimental projectiles developed by the Swedish Defence Research Establishment (FOA), which have cores of a tungsten-cobalt composite with an even greater hardness of 1,800, require still harder ceramics, such as titanium diboride.
Unfortunately, the harder the ceramics the more expensive they are. Therefore, silicon carbide costs 5 to 10 times as much as alumina, which are not cheap themselves, and boron carbide, the hardest of the ceramics, costs 20 times as much. This makes boron carbide too expensive for combat vehicles, and the use of silicon carbide and titanium diboride has been confined to a few prototypes or experimental vehicles, such as the US M8 Armored Gun System and the Bradley Composite IFV.
On the other hand, the use of aluminum oxide ceramics is now well established. Early examples of their use are provided by the Swedish Pbv302 and Canadian M113 armored carriers, which were fitted for the 1990s operations in Bosnia with MEXAS ceramic tile armor developed in Germany by IBD. In the former case, the tiles were applied on the top of RHA and, in the latter, on top of 5083 aluminum armor. A more recent example is provided by the Mowag-designed 8x8 LAV III produced for the Canadian Army, which has MEXAS ceramic tile armor on the outside of its HHS base armor. A similar combination is also to be used on the US version of LAV III, the Stryker Interim Armored Vehicle, and on the 8x8 Anglo/German MRAV/GTK.
The combination of HHS with a facing of alumina tiles results in armor with Em values of more that two against 14.5mm AP. This means that such armor is more than twice as effective as RHA against the most severe of the kinetic-energy forms of attack generally considered to face light combat vehicles in other than major conflicts. A further and more direct measure of the progress in armor protection is provided by a comparison of the areal densities quoted in Tables 1 and 3, which shows that ceramic-faced armor not much heavier than the RHA required to defeat 7.62mm AP can now provide protection against 14.5 AP at point-blank range.
Tables 1 and 3 also indicate that a combination of ceramic tiles with aluminum armor can be more effective in relation to its weight than their combination with HHS. This is to be expected, as backing a hard ceramic facing with another hard material instead of a lower density, energy absorbing layer is not likely to represent the optimum combination.
Effective as they are against single bullets, ceramic tiles fracture under impact because of their brittle nature and have therefore little, if any, ability to resist multiple hits. To overcome this problem Rafael developed what was originally called 'Flexible Ceramic Armor' which, instead of tiles, consisted of rows of small ceramic spheres embedded in an elastomeric matrix. A few of the spheres would be broken by a hit but the damage would be confined to a relatively small area, instead of spreading across a tile, which enables the armor based on them to withstand multiple, closely spaced hits.
Armor based on ceramic spheres embedded in an elastomeric matrix is being developed further by Plasan Sasa, an Israeli company specializing in the protection of light vehicles, which calls it “Smart Armor' or 'Super Multi-Hit Armor Technology. In one of its latest forms it has an Em as high as 2.27 against 14.5mm B32 AP at point-blank range. A similar armor, also of Israeli origin, and consisting on ceramic pellets in an elastomeric matrix is manufactured in France by ARES Protect on SA, under the name LIBA, an acronym for Light Improved Ballistic Armor. This ceramic armor has been adopted for the AAAV under development for the USMC and on which it is to be overlaid on the 2519 aluminum armor structure.

Reactive sandwich armors
A very different approach has had to be adopted to improve the protection of light combat vehicles against shaped charge weapons. Attention in this case has been=>

Table 3
Armors required to resist 14.5mm x 114 AP B32 (steel-cored) bullets at normal impact and point-blank range
Armor material  RHA HHS 5083 7017 7039 Titanium VeryHardSteel+5083 VeryHardSteel+Titanium PerforatedVeryHardSteel+5083 CeramicTiles+HHS CeramicTiles+Alum CeramicSpheres+Alum
Thickness (mm) 41 36 134 97  270 91 45
Areal density (kg/m2)  322 283 356 253 199 192 167 168 152 146 141
Em 1.00 1.14 0.90 1.19 1.27 1.62 1.68 1.93 1.92 2.12 2.19 2.28

□ The aluminum hull of the 13 tonne Alvis Stormer 30 contributes less than a third of the gross vehicle weight.
□ The Dutch-German Fennek uses a combination of aluminum and steel armor for improved mass effectiveness.
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=>generally focussed on the most common of them, namely the Russian-designed RPG-7 grenade launcher which is claimed to have been produced over the past 40 years in 10 different countries and which is widely used throughout the world, by regular forces and terrorist organizations alike.
The standard PG-7M rocket-propelled grenades fired by RPG-7 have an advertised penetration of more than 300mm of RHA. This is much more than the thickness of armor of any light combat vehicle and, even if RHA were replaced by materials more resistant to shaped charge jets, the weight of any kind of passive armor required to defeat them would be too great. In consequence, light combat vehicles have to resort to the alternative of reactive sandwich armor (see IDR 6/1995, pp.59–63).
The most effective of the reactive sandwich armors is explosive reactive armor (ERA). This has been used on many Russian as well as Israeli and other tanks, and against the shaped charge warheads of RPG-7 grenades single ERA sandwiches can produce armor systems with an Em of as much as nine. This leaves the grenades with a residual penetration capability equivalent to about 30mm of RHA, which can be resisted by the armor of at least some light combat vehicles.
The flying back plates of exploding ERA sandwiches can cause damage to the vehicle on which they are fitted if their armor is thin. Nevertheless, ERA has been installed on a number of light combat vehicles. They include IFVs such as the US M2 Bradley, the Spanish Pizarro and an export version of the Russian BMP-3, as well as Israeli M113 armored carriers.
The risk of damage to the vehicles to which they are fitted can be reduced by backing ERA sandwiches with a layer of an inert material followed by an additional steel plate. This adds weight to the back plate of the ERA sandwiches slowing them down when the sandwiches explode and reducing their impact on the armor of vehicles. This type of hybrid, explosive-inert sandwiches has been developed in Israel by Rafael and is more effective against shaped charge jets than ERA sandwiches by themselves. However, protection achieved against the early types of RPG-7 grenades is no longer adequate against the more recently produced PG-7VL grenades which have larger diameter warheads and an advertised penetration of more than 500mm of RHA. Moreover, development of PG-7VL grenades has been followed by that of PG-7VR grenades which have tandem warheads. Their precursor shaped charges are designed to set off ERA sandwiches and thereby to expose target armor to the shaped-charge jet of the main charge, which is claimed to be able to penetrate 600mm of RHA.
A possible answer to the more powerful shaped charges and, even more, to tandem shape charge warheads is tandem ERA, that is armor systems with two ERA sandwiches one behind the other. A Russian defense publication has already claimed that a tank armor system incorporating two ERA sandwiches in tandem and an interlayer of a material capable of delaying the explosion of the second sandwich can defeat the tandem shaped charge warhead of missiles as large as the US AGM-114F Hellfire.
Effective as it might be, the employment of ERA raises several safety issues because of its explosive nature and this has severely restricted its use. Safety issues have also encouraged the development of reactive sandwich armor with energetic but non-explosive interlayers, or ENERA. However, sandwiches of ENERA are generally less effective than those of ERA: a typical ENERA sandwich with a propellan-tlike interlayer is only about half as effective as a comparable ERA sandwich. But some armor systems, which are believed to incorporate more than one ENERA sandwich, although they have been called "passive", appear to have Em up to about eight claimed for them.
The least problematic of the reactive sandwich armors is that with inert sandwich interlayers, or non-explosive reactive armor (NERA). On the other hand, sandwiches of it are generally less effective than those of ENERA, let alone those of ERA. In fact, ERA sandwiches are about four times as individual NERA sandwiches of the same weight. The lower effectiveness of single ENERA sandwiches can be rectified by using several of them, one behind the other with an air gap between them. But this, inevitably, takes up a good deal of space, which may be found on battle tanks but is difficult to find on light combat vehicles.

□ UDLP's MTVL is among the first to use titanium in combination with aluminum, helping it to provide 14.5mm AP protection for the crew while retaining C-130 Hercules air transportability.
□ The cost-effectiveness of composite-constructed vehicles, exemplified by the ACAVP demonstrator produced in the UK by Wickers Defence Systems in association with DERA (now QinetiQ), is the subject of continuing debate. With a fall in the price of carbon fiber, and a reappraisal of its ballistic properties, plans are afoot within QinetiQ to build a new demonstrator with a carbon fiber- reinforced plastic structure.
□ This generic diagram shows the basic construction of reactive armors, versions of which are used in both light and heavy vehicles, In single or multiple sandwiches.
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