Passive armour: the final barrier.


Armoured vehicles hull structures are still mostly made of steel, to which add-on armour packages are bolted. However, the more the basic structure can provide in terms of ballistic and blast protection, the higher the final level of protection will be. Moreover when adopting active defence systems that disrupt the incoming projectiles before impact, fragments still hit the vehicle with a high energy content, commanding a good basic protection.

SSAB of Sweden is one of the world specialists, its family of armour steel being known as Armox. It includes six different types, the number indicating their average Brinell Hardness. While hardness goes in parallel with ballistic protection, toughness is needed to guarantee good blast absorption capacities-two features that won't naturally live together. Formability strengthens the disagreement, as high hardness steels tend to be less formable and often give rise to welding problems.

SSAB steel ballistic performances steadily increased in time: in 1990, 9mm of Armox 5001 were needed to stop an M193/SS92 round travelling at 937 m/s, but ten years later, using Armox 600T, only 6mm were needed. Add another ten years-and 4.5mm of Armox Advance did the same although it has to be unnumbered as its hardness is beyond the. Brinell system scale!

From an initial 70.7 kg/m2 SSAB cut down the weight to 47.1 kg/m2 in ten years, with a further reduction to 35.3 kg/ m2 in the following decade. According to SSAB experts no further dramatic reduction is to be expected in the coming years though, a credible goal for 2020 being 30 kg/m 2. The company's R&D department is working more on improving toughness and formability of existing materiel rather than pushing on hardness, especially that blast is now the main threat. Its Armox 440T, 420480 HBW, is the "energy eater" of choice, and besides its toughness it can be easily formed to obtain, for example, a single-piece hull bottom. Even the harder Armox 500T, 480-540 HBW, is considered for blast protection applications.

As hinted above, the Armox Advanced's main characteristic is hardness, and this material is almost considered by SSAB as ceramic. The company thus strongly advises not to form it or weld it, as it must not be heated above 100[degrees]C if its hardness is to be preserved. How much similar levels of protection and weight might be obtained in the future with more formable materials is the current challenge.

Among new armour steels is of course the Super Bainite introduced in the fall of 2011. Developed by Defence Science and Technology Laboratory in Britain, the new material is produced by Tata Steel UK at Port Talbot and has shown much better performances than standard armour steel. These characteristics do not only result from chemical composition but also from processing, particularly its thermal treatment with air and molten salt as part of the coolants, with the end product offering ballistic performances that are twice those of RHA.

In December 2012 Lockheed Martin UK and the University of Surrey announced a new lighter-weight method of improving the protection and survivability of armoured vehicles. Scientists developed a method of treating ceramic materials to improve the bond strength of both alumina and silicon carbide ceramics to the composite backing, greatly enhancing armour robustness. Connecting ceramic plates to their backing has always been the Achilles' heel of that technology. Results have shownthat the new technique leads to increased bond strength. Tests revealed that when a 14.5mm armour piercing incendiary was fired at the panel it remained intact.

Technology development remains the core business of IBD Deisenroth Engineering while the production of passive solutions is now the responsibility of Rheinmetall Chempro, owned to the tune of 51% by Rheinmetall Defence and 49% by the Deisenroth

With the aim of reducing weight while maintaining protection level, or conversely increasing protection for a given weight, the fourth generation of armour technologies developed by Dr. Ulf Deisenroth applied to different types of materials promise savings of over 40%. These are based on the most recent breakthroughs in the domain of passive protection related to nano-materials, which include nano-cristalline ceramics, nanometric steel and high strength Fibres. In co-operation with steel manufacturers, IBD...

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