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Weight-performance-cost: the golden triangle of transparent armour solutions.

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The need for better situational awareness that surfaced with asymmetric warfare missions, when military units had to move in a civilian environment and avoid collateral damages, led to a dramatic increase in the number of military vehicles featuring large armoured glass surfaces allowing a much better view of the surroundings to the driver and a better understanding of the local situation for soldiers transported in the rear compartment.

Although protection was priority number one, all Mraps featured wide glass surfaces, and while some new vehicles falling in the combat category also began to boast glass windscreens, these were still of reduced surface. With the increase in protection levels, weight, transparency and distortion have become an issue. For a same protection level, standard armoured glass has an areal density that is over four times that of armoured steel, an issue that has to be considered during the design phase. Transparent armour dimensions are also increasing, which poses some problems, especially where new technologies are involved; some armies consider that in a light patrol vehicle a two-panel windscreen with its central strut gives an aggressive aspect, and thus prefer a single glass windscreen. In addition since many vehicles are now built at a base protection level, they have to be then upgraded with add-on armour kits. This means that these must also include adequate transparent armour upgrade, which is of course a huge problem with an overall bolt-on approach.

Weight of tougher windscreens and lateral windows is not the only negative factor, thickness is as well as that increases at a much higher factor compared to opaque armour, not to mention impoverished optical properties, since light transmission tends to decrease and distortion increase with thickness. Faced with a growing market and demand during the past few years, armoured glass manufacturers worked hard to improve the weight-protection conundrum. This was achieved b oth by increasing the efficiency of standard laminates and looking into alternative solutions such as transparent ceramics. In addition to improvements in density versus protection and visual qualities, some manufacturers are also considering transparent armour as an ideal medium to convey more information to the driver and even possibly to the other occupants of the vehicle, with inspiration from the aviation sector's head-up displays--an interesting evolution that might help improve ergonomics and reducing workload.

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Recent missions in areas with heavy temperature gradients (resulting in high temperatures differentials between outside and air-conditioned inside temperatures), sandstorms and so forth, put a considerable strain on transparent armour, with dire consequences on durability. Considering that land vehicles cannot be compared to aircraft in terms of maintenance costs, the latter have to be reduced as much as possible and this should become part of the equation as well as weight and performances--both from industrial and operational use standpoints. Users should indeed also adopt both measures for protecting the vehicles when parked, as well as specific procedures for their cleaning process. Reparability should also be taken into account to rein costs.

THE TRENDS

The purpose of this article is not to review the production of all transparent armour manufacturers around the word (and they are growing by the day: in October 2013 the Mexican Secretaria de la Defensa Nacional announced the creation of an armoured glass manufacturing plant) but to point to the most recent trends in this field. Most producers look at both the civilian and the military market. Those with the largest volumes include American Glass Products (with production facilities in Colombia, Brazil and Peru), and Saint-Gobain Sully in France. America is home to many other companies, like PPG Aerospace, which produces transparent armour to both Stanag protection levels (usually 1 to 3) and US ATPD 2325P levels (1 to 3).

Another major player in the military transparent armour arena is Schott, the Jena-based German company. In addition to its German operation, which produces Stanag-rated transparent armour, the company also has an American arm, Schott North America, which produces US-standard, but International Traffic in Arms Regulations-independent, solutions. The current European product for military use is the Resistan, which ranges from Stanag 4569 Level 1 to 4, in which the identification number indicates the thickness in mm. For its transparent armour production Schott uses the Borofloat 33, a high quality borosilicate glass with outstanding properties that allows a 12-15% weight saving over soda-lime glasses while boasting optimal optical characteristics.

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In 2013 three new types of glass were introduced in the Level 2 and 3 range. For Level 2 applications the NY 52 BF was developed by optimising design and lamination--aimed at vehicles operating in the normal temperature range, that is -32[degrees]C to +49[degrees]C, it has an areal density of 112 kg/m2 and ensures an 86% light transmittance. It is tested against 20 mm Fragment Simulating Projectile (FSP) single hit at 630 m/s and against multi-hit 7.62x39 mm API. Weight and thickness gains are around 10% compared with the 124 kg/m2 of the NY 58 BF, which is however a high temperature range glass (up to +75[degrees]C) and is tested against higher velocity FSP (700 m/s) and 7.62x51 API rounds.

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Two new products are available at Level 3. They allow considerable weight savings over the NY 92 BF although this is qualified for high temperatures and is definitely tougher with its capacity to withstand 20 mm FSP at over 1,250 m/s, and 7.62x54R API, 7.62x51 API and 12.7x109 ball, with an areal density of 195 kg/m2. The new NY 80 BF features a 174 kg/m2 density (10% reduction), testing not including the 12.7 mm, while the NY 69 BF comes at 153 kg/m2 (-22% over NY 92), this being tested only against 7.62x54R API. As for Level 4 Schott proposes two members of its Resistant family, the NY135, at 284 kg/m2, and the NY 194 at 398 kg/m2, both withstanding a 20 mm SFP at over 1,550 m/s and the 14.5x114 API round, although the thinner glass is tested only with single-hit while the thicker is multiple-hit capable.

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According to Schott the NY 194 is the only fully approved and certified full Level 4 solution, as it was certified by the German BAAINBw (the Federal Office of Bundeswehr Equipment, Information Technology and In-Service Support formerly known as BWB). The Resistan catalogue includes numerous other members, the VPAM family meeting EN 1063 and VPAM BRV 2009 standards, and the DV family the ATPD Revision T standards. To better answer market requirements, and considering not only the increase in military production but also that for civilian purposes, Schott has recently converted its Jena flat glass lamination and framing plant into a fully integrated production line that also includes bending, with 500-1,000 mm curvature radius, and edge processing.

Looking ahead Schott is closely looking at new materials, such as transparent ceramics and spinel. Due to Germany's tight road regulations the company considers that optical performances offered by such alternatives might not be accepted for windscreen applications, but given their lighter weight they might well b e suitable for side windows. However costs of such innovative materials are still to be worked out. As for classical laminated glass Schott experts consider that currently available technologies will not allow any major improvements in the coming years, Level 3 being close to the limit that is considered to be around 75 mm thickness and 160 kg/m2 surface density. Schott North America is specialised in glass-ceramics, polycrystalline materials produced through controlled crystallization of base glass essentially through thermal treatments. The treatment produces a 35 nm crystallized surface layer while the rest of the glass-ceramics features an 80% crystallised structure. This material does not provide weight saving, but meets US ATPD-235 standards (though results obtained remaining classified).

Another key player in the armoured glass field is Oran Safety Glass (OSG) from Israel, which is IDF's sole supplier. The company provides flat and curved armoured glass to numerous manufacturers in first tier nations such as the United States, France, Germany, Italy, etc. OSG is particularly focused on the US market though, its armoured glasses equipping two out of three JLTV teams. To meet that goal the company, which runs two plants in Israel, has set up a sister company in Virginia, OSG Inc., in Virginia. OSG is obvio usly striving to lower weights for a given protection level, but it is also aiming at further evolutions, combining different technologies into its products to add amenities such as defrosting with the ability of clearing vision within in 30 seconds at -42[degrees]C.

Using semi-exotic material OSG has recently developed a Level 3 solution at 170 kg/m2, with an 83 mm thickness. In order to extend as much as possible its laminated glass life cycle the company has developed a special sealing to cope with heat, humidity, sand, and air conditioning effects. OSG is also proposing its Crystallised Material (CM) technology, which allows a weight reduction of between 30 and 50% (see table) with thickness reductions ranging from 40 to 60%, bearing in mind that further weight reduction can be achieved in the related frame itself. Here the problem is not only technical but also economical, as ceramic-type glasses tend to cost considerably more than standard armoured glass.

Crystallised material technology enables OSG to produce transparent armour at about three times the cost of laminated glass equivalents. The Israeli company has also developed two new technologies to improve the performance of its laminated glass. The first is known as Rock Strike Glass (RSG) and is aimed at preventing the inner glass layers to shatter in case of impact from high-velocity items like gravel or stones. Not only does this allow the driver to continue with the mission with an only marginally reduced vision, but also in most cases screen will not requite urgent replacement, which saves time and ensures higher fleet availability. As in the military no standards related to this problem has yet been established, OSG's took the French railway standard as a basis, which requires zero damage after a 40 m/sec hit by a 90.5 mm diameter conical object weighing 20 grams; the limit for military use was increased to 140 m/sec, the OSG RSG showing a resistance at over 160 m/s with multiple impact capacity.

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The other technology is known as "Adi" (adi meaning jewel in Hebrew), which was unveiled at DSEI 2013. Today typical laminated glasses have a polycarbonate inner layer preventing the spreading of shards and spall inside the vehicle when the glass is hit. According to OSG the coupling of the glass and polycarbonate tends to accelerate delamination, polycarbonate being also subject to damage due to improper use or cleaning. Statistics provided by the company indicate a life expectancy of three to five years for normal transparent armour in the field. The Adi technology will ensure anti-spall performance sans polycarbonate, plus a double field life cycle. OSG has worked for over two years on this technology. Last ballistic tests were carried out in Fall 2013 and production of Adi glass are starting in 2014.

OSG is also looking at ways of using glass surfaces as display media. Silk-light technology uses a built-in light-driven electronic system that permits to display simple (mostly emergency) messages directly on the armoured glass. Also, a Digital Visual Window allows to integrate an LCD display into transparent armour without decreasing the protection level thanks to an armoured steel overlap, allowing to save space in the vehicle. The display is linked to a separate electronic unit that can be easily repaired and replaced.

Glas und Optik GmbH, better known as GuS, is another major German player. In early September 2013 the German BAAINBw qualified the new Level 3 laminate glass from the company that reduces density from 215 to 170 kg/m2 (20% weight) and thickness from 91 to 83 mm, while extending temperature operating limits to -32[degrees] to +49[degrees]. Moreover its multi-hit capabilities were tested on a triangle with a 120 mm base instead of the usual 300 mm base, and the indent was very limited, the rear polycarbonate sheet job being thus much reduced. Sole supplier of the German Army, GuS has shown its repair capabilities in Afghanistan where stones and rocks damaged some 3,500 windscreens (over 600 Dingos were deployed) many of which were repaired by the company team. GuS also has numerous R&D programs underway, with Plochingen-based CeramTec GmbH in the transparent ceramic field. While protection level seems not to be a major problem, the company finds hurdles in the German road traffic regulations, as the glue that allows to keep the ceramic tiles together generates a visual effect that has still to be evaluated in terms of eye fatigue, headaches and disorientation. Currently GuS is working closely with the BAAINBw to analyse those possible side effects before moving further down the ceramics road.

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Still, in Germany, ESW GmbH, part of the Jenoptik Defense & Civil Systems division, has shown at DSEI 2013 a plastic transparent armour that ensures over 90% light transmission. One of the huge advantages of the Jenoptik solution is that the windshield can be bent, thus making the central bar, typical of military vehicles windshields composed of two flat transparent armoured glass panels, redundant thus ensuring maximum frontal visibility. In addition, the Jenoptik plastic-based transparent armour does not produce any distortion even where the glass is curved. Currently the company proposes two types of surfaces, respectively at Level 2 and Level 3 protection. The former comes at approximately 144 kg/m2 and a thickness of 121 mm, while the latter has an areal density of 238 kg/m2 and a thickness of 201 mm. The Level 3 solution is also being certified for EFP coherent and multi-slug resistance in the 0[degrees] to 45[degrees] arc and for RPG 7 resistance at 45[degrees]. De-icing and EMC protection are available upon request. According to Jenoptik its transparent armoured plastics are able to maintain a high degree of visibility even after a hit.

IBD being one of the major European opaque armour solutions experts, it was clear that a solution had to be found to decrease the weight of transparent armour. Indeed, not only does a typical window area of 3 m2 on a truck weigh around 600 kg, it is also high up on a vehicle with disastrous effects on the center of gravity. With the NanoTech development experience feather in its cap IBD developed a transparent ceramic protection, the key factor being the development of special bonding processes for the assembly of ceramic tiles ("Mosaic Transparent Armour") and the lamination of these assemblies with strong carrier layers to form large window panels.

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Due to the outstanding ballistic performance of the ceramic material and the elastic absorption of the remaining kinetic energy of the threats, the company managed to produce transparent armour panels with a drastically reduced weight. Compared to the 200 kg/m2 of a Stanag 4569 Level 3 standard armoured glass the new technology allows to reduce the weight of the transparent ceramic armour for the same protection to 56 kg/[m.sup.2] only, that is a 72% gain which, in absolute terms for the truck windows taken as an example, would mean 170 kg. According to IBD optical performances of the new transparent ceramic protection are at least as good as those of laminated armour glass, as it is less tinted and shows a lower diffraction, and no bonding edge of the tile assembly appear. Those optical properties also apply to the infrared spectrum, meaning that night vision goggles can be used as well. A Nato country was faced with the option of reducing protection or adding a further front axle to its trucks, but the IBD solution allows either to maintain a single axle configuration and save money, or to double them and increase protection. According to IBD its transparent ceramic armour is fully qualified and is currently in the industrialization phase, with process optimization solely focused on reducing costs; the company's aim is to have a product that is only 50% more expensive than standard glass. However for the time being a cost of less than twice that of current solution is considered viable.

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ArmorLine, a South Carolina-based company part of the Defense Venture Group, has developed an optical grade transparent spinel ceramic that allows to produce transparent armour with a considerable weight saving. The ArmorLine spinel is a polycrystalline material that features extreme hardness and strength, and while it boasts an abrasion resistance that is typical of ceramics, it ensures transmission in the 0.2|rm -5.5[micro]m band, thus allowing applications in the UV (0.2-0.4[micro]m), visible (0.4-0.7[micro]m), near-IR (0.7-3[micro]m), and MWIR (3-5[micro]m) bands, typically used in military applications not only for vehicle transparent armour but also for sensor protection. The advantage of ArmorLine spinel is that it is produced in dimensions that are definitely larger than those of transparent ceramics, current larger panels being around 70 x 50 cm, the company aiming at producing 85 x 60 cm panels within the year, both flat and curved (with a 2,500 mm curvature radius), and reach the half windscreen dimension production, that means 100 x 75 cm flat panels, in 2014.

The ability to supply curved transparent armour items is considered a plus over other systems, allowing vehicles designers to have greater flexibility. Spinel transparent armour, which replaces some layers within a laminated glass, has improved multi-hit resistance and ensures weight and thickness reduction of between 50 and 60%. As an example a laminated armoured glass capable of withstanding a 12.7x99 mm APM2 single shot round has a thickness of 103 mm and an areal density of 227 kg/m2 while the ArmorLine spinel lowers those figures to 49 mm and 100 kg/m2, in other words by 53% and 56% respectively. Those data are confirmed looking at an ATPD 2352 Class 3A transparent, where thickness decreases from 112 to 52 mm and areal density from 249 to 109 kg/m2. ArmorLine is not a laminator however, thus weights mentioned are for non-optimised testing items and could be further optimised. In Stanag parlance, aerial density obtained for Level 2 transparents is around 69 kg/m2 while for Level 3, against 7.62 x 54R B32 API, this is increased to 84 kg/m2.

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Isoclima of Italy started working on transparent armour in the early 1980s, for both civil and military markets, and has since developed proprietary technologies to optimise the lamination of glass and polycarbonate. It has provided most of the Iveco DV LMV glass solutions, tailored to the requirement of the various customers of the 4x4 light multirole vehicle. For example, the transparent adopted on Russian LMVs is capable of withstanding temperatures of between -45[degrees]C and +70[degrees]C, the coupling being here a key element as the polycarbonate thermal expansion coefficient is eight times that of the glass. Among its products we find a Level 2 solution with 58-59 mm thickness and an areal density of 125-130 kg/m2, and aLevel 3 with corresponding data of 79-80 mm and 157-162 kg/m2, both for standard temperature operations.

The company is currently considering new solutions for improving performances while lowering weights; it is thus testing new materials such as spinel and others, although the management is pretty convinced that improvement stays with the complete package and therefore improving glass characteristics as well as those of lamination material, such as films, will allow Isoclima to improve its position on the market. The company also has developed solutions to improve the transparent armour life, such as anti-scratch treatments on the polycarbonate backing as well as a proprietary magnetically fixed outer ply that protects the ballistic window from rock and stone damage known as Antistone Protection Solution (AspS). The removable protective layer is based on a dual sealing magnetic gasket holding an outer protection shield made of external glass and internal tecnopolymer, an air chamber being created between this and the transparent armour. All possible drawbacks were considered and verified, i.e. condensation, optical distortion, etc., tests having shown minimal impact on those characteristics. On the other hand the AspS contributes to hugely reduce maintenance and increase transparent armour life. Many of the solutions developed by Isoclima are due to the involvement of the company in the advanced aerospace transparent solutions.

Caption: To increase transparent armour life, users should adopt ad hoc protection measures in harsh environmental conditions, here M-ATVs parked in Afghanistan. (Armada/Paolo Valpolini)

Caption: To improve performances and lower weights of its transparent armour, Schott of Germany uses Borofloat, a proprietary borosilicate glass that presents very good optical characteristics. (Schott)

Caption: According to BAE Systems its Clearguard castable transparent provides better ballistic performance than their conventional acrylic and polycarbonate counterparts. It is used in monolithic or laminated form to stop fragments and hand gun-fired projectiles. Used as backing layer behind high performance glass, it also provides considerable weight saving. (BAE Systems)

Caption: OSGs Digital Visual Window (ltop) integrates a digital display into the glass without reducing protection, while the Silk-light technology (bottom) allows to inject short warning messages into the windscreen. (OSG)

Caption: Oran Safety Glass of Israel has developed the Adi, a technology that renders inner anti-spall polycarbonate layer redundant, which, according to OSG, doubles the glass field life cycle. (OSG)

Caption: Level II and Level III transparent armour by German GuS. The company supplied the transparent surfaces for the German Dingos used in Afghanistan and is now considering to move on to ceramics. (Armada/Paolo Valpolini)

Caption: IBD Deisenroth has developed transparent ceramic tiles as well as a technology to cement them together that generates transparent armour that saves up to 70% weight compared to conventional laminated glass. (IBD)

Caption: At DSEI2013, Jenoptik exhibited an all-plastic transparent armour. Still heavier and thicker compared to laminates, it has the advantage of showing no distortion when curved. (Armada/Paolo Valpolini)

Caption: ArmorLine is producing the spinel, a polycrystalline material that allows to reduce weight and thickness used in laminated transparent armour. (ArmorLine)

Caption: A 400x 400 mm laminated transparent armour produced using an ArmorLine spinel, seen after six shots. The company aims at producing a half-windscreen by late 2014. (ArmorLine)

Caption: Among the technologies used to increase transparent armour durability, Isoclima developed an encapsulation method that ensures maximum life to its laminates. (Isoclima)

Caption: Isoclima in Italy supplies Iveco with most of the transparent armour for the LMV Lince; here a window after a test firing at the Nettuno proving ground. (Armada/Paolo Valpolini)
COMPARISON BETWEEN EXISTING GLASS AND OSG'S CRYSTALLISED MATERIAL

Protection     Exist. Technol.    CM Technol.     Difference
level Stanag   [kg/[m.sup.2]]    [kg/[m.sup.2]]       %

1                    96                51            46.9
2                    125               71            43.2
3                    190              126            33.7
4                    284              146            48.6
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Title Annotation:Transparent Armour
Author:Valpolini, Paolo
Publication:Armada International
Date:Feb 1, 2014
Words:3855
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