TRANSPARENT ARMOUR

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TABLE OF CONTENTS

TABLE OF CONTENTS ...................................................................................................... I

LIST OF FIGURES ........................................................................................................... III

LIST OF ACRONYMS ..................................................................................................... IV

INTRODUCTION ................................................................................................................ 1

Aim of this paper .............................................................................................................. 2

GLASS ................................................................................................................................... 3

Borosilicate Glass ............................................................................................................. 5

Fused Silica ....................................................................................................................... 6

Laminated Glass ............................................................................................................... 6

Toughened Glass .............................................................................................................. 7

Glass Ceramics ................................................................................................................. 8

Transparency ................................................................................................................. 10

Bullet Resistant Glass .................................................................................................... 11

TRANSPARENT CERAMICS ......................................................................................... 16

Sintering .......................................................................................................................... 17

Hardness ......................................................................................................................... 18

Aluminium Oxynitride Spinel ....................................................................................... 19

Single Crystal Aluminium Oxide .................................................................................. 20

Magnesium Aluminate Spinel ....................................................................................... 20

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POLYMERIC MATERIALS ............................................................................................ 21

Thermoplastics ............................................................................................................... 22

Thermosets ...................................................................................................................... 23

TRANSPARENT ARMOUR SYSTEM ........................................................................... 23

Strike Face Layer ........................................................................................................... 25

Intermediate Layer ........................................................................................................ 26

Spall Layer ...................................................................................................................... 28

Ballistics .......................................................................................................................... 29

CONCLUSION ................................................................................................................... 30

APPENDIX A ..................................................................................................................... 32

APPENDIX B ..................................................................................................................... 38

APPENDIX C……………………………………………………………………………..40

REFERENCES ................................................................................................................... 43

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LIST OF FIGURES

Figure 1: Soda Lime Glass ………………………… Page 5

Figure 2: Stresses in Toughened Glass ………………………… Page 7

Figure 3: Traditional Structure of a Transparent Armour System……… Page 12

Figure 4: Modern Designs of Transparent Armour Systems…………… Page 14

Figure 5: Transparent Armour System ………………………… Page 25

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LIST OF ACRONYMS

AlON Aluminium Oxynitride Spinel

ARL United States Army Research Laboratory

ASP Anti-Spall Polycarbonate

ASK Armour Survivability Kit

EOD Explosive Ordnance Disposal

HMMWV High-Mobility Multipurpose Wheeled Vehicle

IED Improvised Explosive Devices

IR Infrared

NVE Night Vision Equipment

PC Polycarbonate

PMMA Poly-Methyl Methacrylate (Acrylic)

PU Polyurethane

PVB Polyvinyl Butyral

UV Ultraviolet

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INTRODUCTION

Transparent armour, known colloquially as bullet proof glass, is a material or layers of

functionally integrated materials constructed to be optically transparent and offer protection

from fragmentation or ballistic impacts. Transparent armour is one of the most critical

components of light armoured vehicles. This class of materials is used in such diverse

applications as protective visors for non-combat usage, including riot control or explosive

ordinance disposal (EOD) actions. Its most extensive role however is to protect vehicle

occupants from terrorist actions or other hostile conflict by providing blast and ballistic

protection while retaining structural integrity and optical transparency. In many cases the

occupants of the vehicle who are visible through the windows are the main target of direct

fire attacks. Various systems are designed to defeat different threats with a primary

requirement to provide multi-hit capability with minimised distortion of the surrounding

area. There are several parameters that must be optimised such as weight, compatibility

with night vision equipment (NVE), space efficiency and cost versus performance. [1], [2].

To ensure sufficient visibility the transparent armour system must have adequate light

transmission values at specified ranges in the visible and infrared light spectra [3].

As threats have escalated and weaponry has become more advanced it is imperative to

develop vehicle protection systems. Recent military operations in Iraq and Afghanistan

demonstrate the critical importance of transparent armour in military vehicles for occupant

safety. This is evidenced by the many threat specific transparent armour add-ons or retro

fits to up-armour a variety of combat vehicles [2]. As most current warfare is asymmetrical

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and unconventional mainly in urban or built up areas, the ability to fire and manoeuvre can

be somewhat curtailed giving rise to the requirement for better vehicular protection. With

the onset of many new peacekeeping roles within the military, it is necessary to provide a

greater degree of protection to the individual soldier. Vehicles in many operational theatres

are facing increased threats from armed insurgents and improvised explosive devices

(IEDs). Today, we face adversaries that seemingly have no qualms at sacrificing their lives

or those of innocent bystanders in an attempt to inflict maximum damage on military

personnel [17]. Bullet projectiles behave differently than fragments from an IED, therefore

specific solutions can be made to better protect against one threat or the other. [3].

After the recent shooting of two policemen in America, New York State authorities are in

the process of passing laws to upgrade all their police cars with transparent armour [16].

Military and police forces in Europe have recently dealt with numerous riots and terrorist

activity (Copenhagen, Athens and Paris). Transparent armour is an essential aspect of most

vehicles called to assist as aid to civil power. Ireland has been fortunate to date that terrorist

activities did not intensify south of our border and that recent violent civil unrest has been

modest. Adequate protection is necessary to enable personnel face the assessed threats with

confidence and safety. The windows and windshield are usually the most targeted areas of

the vehicle and have to provide protection not only against small arms ammunition but

against blast waves and fragments from detonations (e.g. IED’s). [3],[41].

Aim of this paper

This paper will explore the evolution of modern transparent armour and the effectiveness

and efficiency of current day vehicular transparent armour. It will also explore the design

and provide material selection guidelines for transparent armour systems. The aim of this

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paper is to provide the reader with a detailed knowledge of how optically transparent

materials can provide protection from ballistic impacts or fragmentation in ground vehicles.

It is the intention of this paper to provide concise information by conducting a review of

literature in the public domain to assist in the selection of suitable transparent armour

systems for various threat levels.

GLASS

People had used naturally formed glass, especially black volcanic obsidian glass before

learning how to make glass. Stone-age man has used obsidian and tektites to craft weapons

and create decorative objects. The ancient Roman historian Pliny suggested that

Phoenicians had made the first glass in Syria around 5000BC. However to date

archaeological evidence records the first man made glass was in Eastern Mesopotamia and

Egypt around 3500BC. The first glassmaking manual from the library of the Assyrian king

Ashurbanipal (669-626 BC) dates back to around 650BC.

The art of glass making flourished in the Roman Empire and spread across Western Europe

and the Mediterranean. Glass was one of the most important items of trade beyond the

borders of the Roman Empire. The Romans were the first ones to use glass for architectural

purposes, when clear glass was discovered in Alexandria around AD 100.

A flourishing glass industry was developed in Europe at the end of the 13th century when

the glass industry was established in Venice at the time of the Crusades (AD 1096-1270).

In 1291, equipment for glassmaking was transferred to the Venetian island of Murano

where “cristallo” (colourless glass) was invented by Angelo Barovier. 14th Century

Murano glassmakers were allowed to wear swords, enjoyed immunity from prosecution by

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the Venetian state and found their daughters married into Venice’s most affluent families.

However glass makers were not allowed to leave the Venetian Republic in order to

safeguard the glass-blowing manufacturing techniques. Murano’s glassmakers successfully

managed to hold a monopoly on quality glassmaking for centuries, innovating constantly

through development and refinement of technologies and inventions. Among these were

crystalline glass, smalto enamelled glass, aventurine glass with threads of gold, millefiori

multicolored glass, lattimo milk glass and imitation gemstones made of glass. Despite the

best efforts of the Venetian artisans who dominated the glass industry to keep the

technology secret, it eventually spread around Europe.

Glassmaking was slow and costly until revolutionised by the new technique of glass

blowing at the end of the first century, making glass production easier, faster and cheaper.

In Germany and other northern European countries glassmaking became important by the

late 1400`s and during the early 1500`s it became significant in England. The tools and

techniques of glass blowing have changed very little over the centuries. The English

glassmaker George Ravenscroft (1618-1681) invented lead crystal glass in 1674 by the

addition of lead oxide to Venetian glass. In the late 1950`s Sir Alastair Pilkington

introduced a float glass production method by which 90% of flat glass is still manufactured

today in what has become a hi-tech manufacturing industry. [6], [7].

In its most basic form, glass is made from 72% quartz sand (silica), which melts at about

1700°C. Adding a flux such as soda ash (15% sodium carbonate) lowers this extremely

high melting point to a more feasible 1316°C, however this makes the glass water soluble.

Lime (10%) is added to the mixture of dry ingredients (the batch) in the form of crushed

stone as a stabilizer to help the glass resist moisture.

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The remaining 3% is made up of impurities found in the other ingredients (such as iron or

magnesium). This formula (Figure 1) is a basic type of soda-lime glass, still the most

common form of glass—it represents 90% of the glass made today [4].

Figure 1 Soda Lime Glass - [4] Toledo museum of modern art

Traditionally, soda-lime glass (float glass) is used in transparent armour applications due to

its good combination of stiffness, compressive strength, and durability [2]. Borosilicate

glass and fused silica glass are also commonly used in transparent armour.

Borosilicate Glass

Boron which is a metalloid or semi-metal is added to the glass mix during manufacture to

make borosilicate glass. It has a low thermal expansion coefficient, excellent thermal

properties and a high softening point (820°C). Borosilicate glass is commonly used in the

internal layer of bullet resistant glass and widely used for laboratory glassware. It is highly

resistant to attack from water, acids, salt solutions, organic solvents and halogens, however

strong alkaline solutions cause rapid corrosion of this glass. Its chemical composition is

SiO2 = 80.6%, B2O3 = 13.0%, Na2O = 4.0% and Al2O3 = 2.3%. It is a glass that can be

easily fabricated, making it more economical than most other glasses. [39] [5].

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Fused Silica

Silica (SiO2- silicon dioxide and sand) is one of the chief constituents of the earth’s crust

and is present mainly in the form of quartz which is a colourless transparent crystalline and

when fused at 2000°C becomes a vitreous material. Fused Silica Glass is a unique material

with a very high degree of purity (99.99%), high temperature resistance, thermal shock

resistance, good electrical insulation, chemical inertness and unmatched optical

transparency. Fused silica is commonly used in the production processes of the semi-

conductor industries. It also has excellent thermal properties with an extremely low

coefficient of expansion and a high resistance to thermal shock. It has good mechanical

strength and almost perfect elasticity.

Laminated Glass

In 1909, a French chemist Edouard Benedictus, invented laminated glass and called it

"Triplex". Laminated glass (6.38mm) typically consists of two sheets of 3mm glass with a

.38mm interlayer usually of polyvinyl butyral (PVB)1. This configuration strengthens the

glass and helps it to stay together when damaged, making it safer than normal glass. These

features make it ideal for car windscreens and help prevent ingress of objects. It also has

improved acoustic and thermal comfort qualities and can filter out 99% of harmful UV

sunlight. Delamination of the glass and plastic layers has been observed at higher

temperatures resulting in lower visibility. Brittleness of the interlaminate adhesives at low

temperatures has been overcome by using urethane [3].

1 Polyvinyl Butyral is a resin usually used for applications that require strong binding, optical clarity, adhesion

to many surfaces, toughness and flexibility. It is prepared from polyvinyl alcohol by reaction with

butyraldehyde.

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Toughened glass

Toughened glass starts life as float glass which is made from a mixture of sand, limestone,

soda ash, dolomite, iron oxide and salt cake. It must be pre-cut before the toughening

process as it would shatter if cut in its toughened state. In the toughening process, the

surfaces of the glass are heated in a furnace to over 600°C and then cooled rapidly by a

blast of air over a period of between 3 and 10 seconds.

As a result, the surfaces shrink, and (at first) tensile stresses develop on the surfaces. As the

bulk of the glass begins to cool, it contracts. The already solidified surfaces of the glass are

then forced to contract, and consequently, they develop residual compressive surface

stresses (Fig. 2), while the interior zone develops compensating tensile stresses. The

tension zone in the core of the glass takes up about 60% of the cross-sectional area of the

glass. Compressive surface stresses improve the strength of the glass in the same way that

they do in other materials.

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The toughened glass has a greater resistance to thermal stresses, thermal shock and has

improved flexural and tensile strength. The following characteristics remain unchanged; •

Colour, • Clarity, • Chemical composition, • Light transmission, • Hardness, • Specific

gravity, • Expansion coefficient, • Softening point, • Thermal conductivity, • Solar

transmittance, • Stiffness. [5].

The higher the coefficient of thermal expansion of the glass and the lower its thermal

conductivity, the higher the level of residual stresses develops and the stronger the glass

becomes. Thermal toughening takes a relatively short time (minutes) and can be applied to

most glasses. The high amount of energy stored in residual stresses causes tempered glass

to shatter into a large number of pieces when broken, which are less sharp and hazardous

than those from ordinary glass. Instead of normal glass, toughened glass and polycarbonate

can also be used to increase strength - for transparent armour, for instance. Research

indicates that lower light transmission levels occur when the transparent armour system

contains “green” glass, or if the solution includes a large amount of plastic. Green glass is

caused by a high concentration of iron which tints the glass a slight shade of green and is

cheaper to process than clear white water glass because of impurities. This gives low

visibility in normal conditions and almost no visibility when using NVE. This green glass

has recently been rejected by the US military. [3] [13]. More modern materials are

constantly being considered in the search for clearer, lighter, stronger glass.

Glass Ceramics

Although glass ceramics exist in nature, synthetic ceramics were not discovered until 1953

by Stanley Donald Stookey. Like other discoveries in the glass world, glass ceramics were

discovered by accident when Stookey overheated lithium disilicate glass to 900°C. He

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feared that he had ruined the furnace but observed a white material which had not changed

shape. When accidentally dropped it did not break and so he created the first glass ceramic

which led to the development of transparent cookware. [28].

The ballistic properties of glass can be increased by chemical strengthening or thermal

treatments. Certain glasses can be crystallised or devitrified to produce transparent glass

ceramics with structural properties similar to those of crystalline ceramics. Glass ceramics

are normally produced by a standard glass-manufacturing process after which the glass

article is shaped, cooled and reheated above its glass transition temperature where it

partially crystallises in the interior. Glass ceramics can be produced by controlled internal

crystallisation during the cooling process or by sintering2.

TransArm™ is a weight efficient glass ceramic recrystallized form of lithium alumino-

silicate-based glass developed by Alston UK Ltd for use in transparent armour with all the

workability of an amorphous glass. It has superior weight efficiency against ball rounds and

small fragments [29]. [17]. Some of the main advantages of glass ceramics are, zero or low

porosity, cost efficient mass production and ease of processing into intricate shapes. The

fabrication methods are similar to conventional glass manufacturing and can produce large

material shapes. The nanostructure or microstructure can be designed for a given

application and it is possible to combine a variety of desired properties. Little has been

published and patented on the use of glass-ceramics in transparent armour, compared with

other applications. This is because of the sensitive nature of military-related research. [26]

Although the ballistic protection of transparent armour is essential, another important

aspect is optical clarity

2Coalesce into a solid or porous mass by means of heating (and usually also compression) without

liquefaction. [34].

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Transparency

Glass is a special kind of solid known as an amorphous solid which forms when a solid

substance is melted at high temperatures and then cooled rapidly. This is a state of matter in

which the atoms and molecules are locked into place randomly rather than forming neat

orderly crystals. As a result, glasses are mechanically rigid like solids, yet have the

disordered arrangement of molecules like liquids. Glasses have all of the properties of

ceramics, durability, strength and brittleness, high electrical and thermal resistance, and

lack of chemical reactivity. Oxide glass, like the commercial glass you find in sheet glass,

plate glass, containers and light bulbs is transparent to a range of wavelengths known as

visible light. “In science and technology the word transparent is used for those components

that show clear images regardless of the distance between the object and the transparent

window. Clear transparency is achieved when after transmission through the window the

light does not undergo noticeable absorption or scattering. This applies, for example, to

some glasses, single-crystalline and polycrystalline transparent ceramics”. [25].

Transparency is one of the fundamentals of quantum mechanics.

Electrons surround the nucleus of an atom occupying different energy levels and to move to

a higher energy level they must gain energy, or release energy to move to a lower energy

level. When a photon - the smallest particles of light - interacts with a solid substance, one

of three things can happen, the substance absorbs the photon, the substance reflects the

photon or the substance allows the photon to pass through. The latter happens in glass

which is known as transmission where the photon does not have sufficient energy to excite

and react with a glass electron. Photons of visible light travel through glass instead of being

absorbed or reflected making glass transparent. This is not true of wavelengths smaller than

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visible light where ultraviolet light cannot pass through most oxide glasses, such as window

panes. [6]. Impurities in glass can give rise to reflection as colors.

To be functional the transparent armour system must have an optimum level of light

transmission through a selected range of the visible light spectrum. Otherwise the driver

may have a difficult time seeing the road and the other occupants may not be able to detect

threats to the vehicle. As the transparent armour system increases in thickness there is a

higher probability of finding defects in the light transmission and compatibility with NVE.

[3].

Many military applications require materials that are highly transparent in the ultraviolet,

visible and through the mid infrared ranges with low scattering losses, low reflectance and

low absorbance. For a ceramic to become transparent, it should be poreless and have

optically perfect crystal boundaries and crystals. Transparency alone is not enough for glass

in warfare situations. These materials must endure stresses encountered in manufacturing,

transport to theatre, NVE use, deployment in service, or ultimately ballistic impacts.

Ballistic properties and environmental durability are critically important properties in the

military context [11].

Bullet Resistant Glass

While glass-based transparent armour systems are considered heavy, glass remains an

important constituent material in transparent armour applications, due primarily to low cost

and a relative ease of production of curved panels (aircraft mainly).

Transparent armour systems are traditionally constructed as laminates of soda-lime glass

laminate adhesive bonded with polymeric inter-layers (mainly polyurethane or PVB),

Figure 3.

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Figure 3. Traditional structure of a transparent armour system based on glass laminates and

polymeric inter-layers. (a) Bless and Chen [13], Dolan [3] and Grugicic, Bell & Pandurangan

[2].

Due to a relatively high density of glass in these systems, the single and multi-hit

penetration resistance is in direct relation to the laminate thickness. The conventional

approach to increased protection is to add more layers of glass to increase multi-hit

protection in order to obtain the required level of vehicle occupant protection. This

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solution is highly impractical as it leads to: (a) increased vehicle weight; (b) reduced

vehicle cabin space; (c) increased optical distortions; and (d) reduced optical

clarity/transparency. The transparent armour element of the add-on Armour Survivability

Kit (ASK) employed to up-armour HMMWVs contributed to over 30% of the vehicle

weight while providing only 15% of the vehicle’s external coverage.[17][2]. The added

transparent armour weight can be significant, often requiring modification of the

suspension and engine transmission to maintain vehicle performance and payload capacity.

[17]. To overcome these limitations and enhance the ability to fight, new lighter transparent

armour solutions are being sought and developed. [3]. Developing lighter weight solutions

with improved protection will allow transition of these armour upgrade kits to vehicles

without dramatically impacting mission capability [17].

The development of modern armour systems is driven by the demand for lightweight

solutions that enable soldiers and vehicles to be highly mobile, carry out their mission, and

return home safely. Protection must be provided from a wide variety of bullets and

fragments, and must not hinder the soldier’s ability to do their job. Among the transparent

materials available, new material systems being explored to meet the requirements for

ballistic applications include crystalline ceramics, new polymer materials, new interlayer

technologies, and new laminate designs. Plate glass (soda-lime-silica) has been the most

common glass used due to its low cost, but greater requirements for the optical properties

and ballistic performance have generated the need for new materials.

Recent transparent armour systems consist of three functional layers separated: (a) a

projectile-blunting/distorting/eroding/fragmenting hard strike face; (b) energy-absorbing,

crack-arresting, thermal- expansion-mismatch mitigating intermediate layer and (c) a

fragmented-armour debris containment spall-liner/backing layer. Transparent ceramic as a

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strike face improves the ballistic performance further while reducing the system weight.

The three-functional-layer transparent armour system is displayed in Figure 4 below. This

figure illustrates that the strike face is made of glass, glass ceramic or transparent ceramics,

the intermediate layers are made of glass or Poly-Methyl Methacrylate (PMMA) while the

backing layer is composed of Polycarbonate (PC).[2].

Figure 4. Modern three-functional-layer designs of transparent armour systems: Patel, Glide,

Dehmar and McCauley [1] and Grujicic et al [2].

The design and testing of transparent laminates for ballistic protection is still mainly an

empirical process due to the number of parameters influencing the performance, like

number, thickness and type of the glass layers, thickness and type of the bonding layers,

and the polymer backing. Several glasses are used in transparent armour, such as normal

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plate glass, borosilicate glasses, and fused silica, which further extend the number of

parameters to be considered. As mentioned earlier, the development of new transparent

armour systems is done almost exclusively using legacy designs, prior experience and

empirical approaches for these complicated ballistic-protection systems. The lack of basic

understanding of the deformation/fracture behaviour of transparent armour materials and

the effect of their interactions/ integration has resulted in the absence of basic design

guidelines or principles. Shortcomings of the transparent armour systems are often

discovered after deployment, resulting in costly maintenance or repair and increased

vehicle downtimes. A cost analysis study on HMMWVs glass armour systems (prepared by

the US Army, TACOM Cost & Systems Analysis Directorate [30]), revealed that $5.2

million per month was spent in 2005 on the replacement of windshield and door windows.

Subsequent years showed a continuous rise in costs as the number of up-armoured

HMMWVs deployed doubled and the demand for transparent armour windscreens

increased by 1.3 times and door windows increased by 6.6 times. This was not due to

insurgent attacks alone but due to sandstorm damage, rock strikes, improper removal and

installation. Loss of transparency was caused by improper curing, environment induced

delamination and surface degradation due in some cases to improper cleaning.

Empirical testing is a time consuming and expensive business. Partly out of concern for

insufficient safety in the security sector due to failure of industrial components, Ramenani

and Rothe [24] conducted a computer based exploration of a bullet proof glass laminate

structure impacted by a projectile. The study of mechanical parameters by computer

simulated ballistic tests using comparison data from existing tests would optimise the safety

and predict the ballistic performance of a large number of transparent armour systems. The

ability to computer analyse and evaluate numerous design concepts of transparent armour

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by the use of modern hydrocodes should provide a cost effective means of producing

specific effective threat protection. Rapidly changing warfare environments will require

lightweight, threat adjustable, multifunctional, and affordable armour, which current glass

and PC technologies are not expected to meet. New material systems are constantly being

developed in an attempt to meet these requirements. It is necessary to understand the nature

and properties of materials that are available for transparent armour systems. [24], [2], [1].

TRANSPARENT CERAMICS

Transparent crystalline ceramics are used in the most advanced military and civilian

transparent armour systems to defeat advanced lethal threats due to their exceptional

hardness and compressive strength. The major challenges for these materials are cost,

available sizes, and the ability to produce curved products at reasonable delivery costs.

Transparent ceramics that are single crystal are size limited, expensive to produce which

limits their scale of production and therefore their applications. Many transparent ceramics

are single crystal materials grown from the melt or by flame processes making the growth

and machining of them an expensive task. This limits their scale up of production and

therefore their range of applications. Most of these problems can be solved with the use of

polycrystalline materials as they show similar mechanical, chemical and thermal stability

compared to single crystals.[31] [9] [25].

Polycrystalline means that the material is composed of millions of very small grains while

single crystalline means the whole material is one single grain. [38]. Transparent

Polycrystalline ceramics have more versatile properties and different advantages such as,

low cost, can be produced in complex shapes, are not size limited, mass production and

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ease of manufacture. Most ceramic materials, such as alumina and its compounds, are

formed from fine powders, yielding a fine grained polycrystalline microstructure which is

compatible to the wavelength of visible light.

Sintering

Polycrystalline materials can be produced in complex geometries using conventional

ceramic forming techniques such as pressing and casting. The fine grain metallic powders

are transformed into transparent ceramics by a complex process called sintering. The

processing in conventional fabrication of ceramics can be divided in two main parts;

formation of green body and firing. Both of which must be carefully controlled in order to

avoid residual porosity in the final material. The first part involves the preparation of a

shaped green body from ceramic powders by mixing, consolidation and debinding. The

mixing is the preparation of ceramic powders by adding of dispersants or pH controllers

and the incorporation of binders and other additives. Consolidation is completed after

preparing the conditioned powders and debinding is the process for removing the additives

used in previous actions before sintering is required. A green body is shaped from this

process which is sintered by heating at high temperature in order to eliminate porosity and

obtain the desired microstructure. The microstructure evolution has to be controlled during

sintering when the desired objective is transparency and even then it may be necessary to

carry out an additional process. The initial preparation of the ceramic powder and the

nanograin size also has an outcome on the final product. [25] [31]. Krell is of the opinion

that at extremely small grain sizes (less than 100nm) the hardness will deteriorate because

the material consists mainly of grain boundaries. Krell is to shortly publish a new paper in

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the journal of the European Ceramic Society on the experimental analysis of negative effect

grain sizes (< 100nm). The paper is called "A. Krell: Comment on High-pressure spark

plasma sintering (SPS) of transparent polycrystalline magnesium aluminate spinel

(PMAS)" by M. Sokol, S. Kalabukhov, M.P. Dariel, and N. Frage ". [38].

Hardness

The hardness of ceramics is somewhat dependant on the decreasing grain size which can

cause reduced dislocation mobility and higher density. This ballistic mass efficiency

increases with the hardness of ceramic armour. Experimentation has shown that ceramic

armour should be as hard as or harder than the projectile that it intends to defeat. Hardness

values can also be used to generate other property values that may be relevant to ballistic

performance, like elastic values, yield strength and fracture toughness. Swab sees the best

means of measuring the hardness of armour ceramics is the Knoop3 indentation process.

[37] [40]. Krell agrees with the Knoop testing method and the idea of using a heavy test

load rather than results called micro hardness which are got by low test loads and are

technically irrelevant. [38]

Three main transparent ceramics are emerging as highly promising alternatives to current

glass technologies due to their excellent strength to weight ratio and superior hardness.

These are Al23O27N5 aluminium oxynitride spinel4 (AION) a polycrystalline ceramic, Al2O3

single crystal transparent ceramic (Sapphire) and MgAl2O4 magnesium aluminate spinel

(Spinel). Transparent ceramic when used as a front-ply (strike face) has been shown to

further improve the ballistic performance while reducing the system weight. [1].

3 Knoop method is the measurement of indentation caused when a weigh is applied to the material.

4 Spinel refers to a ceramic material having a spinel crystal structure such as MgAl2O4.

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Aluminium Oxynitride Spinel (AlON) is a cubic material and one of the leading

candidates for transparent armour. The incorporation of nitrogen into an aluminium oxide

stabilizes a crystalline spinel phase, which due to its cubic crystal structure, is an isotropic5

material that can be produced as a transparent ceramic polycrystalline nanomaterial. AlON

is optically transparent (≥80%) in the near ultraviolet, visible and near infrared regions of

the electromagnetic spectrum [25]. It is four times harder than fused silica glass and is up to

five times more expensive. It is 85% as hard as sapphire and nearly 15% harder than

magnesium aluminate spinel. It is relatively new technology only available in limited

dimensions with high production costs mainly due to the post manufacturing polishing

costs, particularly for transparent armour where optics are important. The hardness of

AlON approaches that of single crystal sapphire which makes it the hardest polycrystalline

transparent currently commercially available. The combination of high hardness and elastic

modulus makes AlON a leading candidate material for transparent armour applications,

followed by magnesium-spinel and single-crystal sapphire. Sub-micron grain-size AION

has been found to match or outperform sapphire and is currently manufactured only by

Surmet Corporation (ALON™) [22]. It is highly scratch resistant with low chemical

reactivity and has successfully withstood single-hit and multi-hit projectile threats,

including 30 calibre and 50 calibre amour piercing (AP) rounds in tests conducted by

Surmet. It outperformed glass armour and at less than half the thickness it reduced overall

weight by 60%. Sintered Al2O3 with sub-μm grain size is the hardest of all transparent

armour (including sapphire). [31] [2].

5 Isotopic – having uniform physical properties in all directions. [34]

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Single Crystal Aluminium Oxide (Sapphire) is a transparent ceramic possessing a

rhombohedral crystal structure and its properties which are anisotropic6 vary with

crystallographic orientation. It is well established technology and is currently available

from several manufacturers, but it is costly due to the high processing temperature, the

machining costs to cut parts out of single crystal boules and final polishing requirements.

Windows require a high degree of mechanical polishing with diamond pastes to achieve

optical clarity and low haze. Sapphire has high stiffness and hardness, intermediate density

and high chemical resistance. [25].

Magnesium Aluminate Spinel (Spinel)) is a transparent ceramic with a cubic crystal

structure. This material has excellent optical transmission and high values of hardness.

Spinel offers some advantages over AlON as it is capable of being processed at much lower

temperatures and possesses superior optical properties within the infrared region. [25] It is

also less expensive due to the commercial availability of its powder in bulk quantities.

Spinel panels are still mainly available only for research applications and

structural/mechanical properties are comparable to, although somewhat lower than, those of

sapphire or AlON.

Classified ballistic tests conducted at the United States Army Research Laboratory (ARL)

in Aberdeen, Md., compared current glass based transparent armour with three transparent

ceramic armour materials: AlON, magnesium-spinel, and single crystal sapphire. The tests

showed that AlON resisted penetration 10 % better than magnesium-spinel, 20% better than

sapphire, and 1.5 times better than conventional glass based laminate armour. [2].

6 Anisotropic – having different physical properties in different directions. [34]

21

POLYMERIC MATERIALS

In ground-vehicle transparent armour applications, amorphous glassy polymers are

primarily used as intermediate or spall/backing layers. Structural properties of these

materials remain of primary concern and additional properties such as the ability to

withstand thermal, chemical, ultra-violet radiation, humidity and other environmental or in-

service hazards are also critical. There are two distinct groups of glassy polymers which are

classified in relation to their physical and thermo-mechanical properties as thermoplastics

and thermosets. Thermoplastics are linear or branched polymers that become soft and

deformable upon heating. Thermosets are rigid and possess an interconnected three-

dimensional network that limits flow under elevated temperatures. Transparent polymers

can be fabricated with sufficiently high strength and stiffness and developed as lightweight,

low cost alternatives to traditional glass components. Unlike glass, the physical properties

of amorphous polymers vary significantly with temperature and rate of deformation.

Material characteristics of a polymer change from being a rigid glass to a rubbery-like

structure once heated above a critical temperature known as the glass transition

temperature. Currently, both thermoplastics like PMMA and PC and thermosets like

Polyurethane (PU) are used in ground-vehicle transparent armour applications. Transparent

plastics are currently limited in armour applications because of durability and optical

properties. [2], [1], [17].

Thermoplastics

Polycarbonates (PC), polymers containing carbonate groups, is the most common

inexpensive easily formed or moulded plastic used for transparent armour applications.

Polycarbonates were first discovered in 1898 by Alfred Einhorn, a German scientist

22

working in Munich University and not commercialised until the late 1950’s. PC is currently

used in applications such as goggles, spectacles, visors, ballistic shields for EOD personnel,

and laser protection goggles, but is also used as a spall backing material for advanced

threats as it offers excellent ballistic protection against small fragments. It is more effective

in the thinner dimensions required for individual protection than in the thicker sections

required for vehicle protection. PC has impact toughness almost three hundred times

tougher than single strength glass and has better flame and fire resistance than PMMA. It is

however susceptible to surface degradation from abrasion, rock damage, UV radiation,

organic solvents and requires UV stabilisers and hard surface coatings for durability. PC is

less brittle than PMMA and is used where impact performance is most critical. [2], [17].

PMMA (acrylic) also known as Perspex, has however better impact resistance than most

types of glass and is commonly used as a substitute for glass housings or enclosures, where

hardness, optical clarity, and ultraviolet (UV) stability requirements are essential. It is used

as bullet resistant glazing for protecting against handgun threats and was used in World

War II for lightweight domes and canopies on aircraft. PMMA is manufactured in sheet

form which can be thermally formed into complex shapes or cast for use in transparent

armour systems. PC has been used by military personnel for aircrew visors and sun, wind,

and dust goggles since the early 1970’s providing protection from small fragments. It is

currently used in applications such as goggles, spectacles, visors, face shields, laser

protection goggles, and is also used as a spall backing material for enhanced protection

from more advanced threats. It has been found to be more effective in the thinner

dimensions required for individual protection than in the thicker sections required for

vehicle protection. Research continues into the use of new thermoplastic polymers such as

transparent nylons for improved ballistic protection. [2], [17].

23

Thermosets

Advances are being made in new PU with improved optical properties which has performed

better on an equal weight basis than PC or PMMA. The use of specially formulated

urethanes in transparent armour systems has become quite common. PU’s have a unique

morphology, possessing a combination of hard and soft domains. The properties of a PU

can be tailored to specific applications by adjusting the size and ordering of these domains,

yielding materials that range from being rigid and brittle, like a glass, to flexible and

ductile, like an elastomer. Thermoset PU’s can be processed via casting or liquid injection

moulding and recently the optical properties of PU have been much improved. A ballistic

evaluation of an all polyurethane visor showed that it performed better than both PC and

PMMA, on an equal weight basis. This new polyurethane with improved optical properties

shows promise as a replacement for polycarbonate as visor or spall backing material. [17].

TRANSPARENT ARMOUR SYSTEM

Apart from ballistic protection from shrapnel and bullets, today’s armour vehicle must also

withstand a variety of non-impact threats such as electronic, blast, environmental, optical

and maintenance. [33] A typical transparent armour system consists of several layers of

glass with polymer interlayers and backing as in Figure 5 (p.25). There are a high number

of parameters influencing the performance, like transparent ceramic front layer, number,

thickness and type of the glass layers, thickness and type of the bonding layers and the

polymer backing. The fundamental difficulty in the development of a transparent armour

24

system is that some degree of thickness of the components is imperative for obtaining a

high protective strength, however light transmission decreases and specific weight

increases with increasing thickness.

The final objective is, therefore, a transparent material of high ballistic mass efficiency

which permits the design of thinner windows. [31]. Most modern armour systems consist of

three layers, the strike face layer, the intermediate layer and the spall layer. The plies or

layers are joined by thin adhesive inter-layers that mitigate the potential thermal-expansion

mismatch effects between the adjoining layers. Simplistically, the transparent armour

suffers initial penetration which distorts and erodes the projectile followed by fragmented

striking and damage of the ply material. Subsequent layers may not be visibly fractured, but

the stress state has changed from the pre-impact condition. The physical relationship

between the initial impact and the intermediate and backing materials is complex and the

effects on the overall microstructure of the transparent armour system can vary greatly.

Subsequent impacts will in each case strike a system that has altered due to numerous

complex stresses and strains. The extent of the effect of different material properties on the

ballistic mass efficiency of transparent armour systems is highly dependent on the type and

the degree of interaction/ integration of different functional layers. The ultimate failure due

to impact events is a function of the temporal and spatial interaction of the macro-stresses

at the macro-, micro- and nano-structural scale. [2], [32].

25

Figure 5. Patel, Hsieh and Gilde 2006 [18], modified O’Dwyer 2015.

Strike Face Layer

The two main mechanisms for projectile defeat in the strike face layer are a high ability to

blunt the projectile through prolonged interfacial dwelling (contact-surface dwelling) and

the mechanical deformation, erosion and fragmentation of the projectile. Therefore the first

ply is usually a hard face material with high penetration resistance giving it the ability to

break up or deform projectiles upon impact (Figure 5). The selected material should have a

good combination of high stiffness and high inelastic deformation resistance to maximise

the potential for projectile defeat. The strike face needs high optical transparency in the

visible and IR wavelength ranges with good low velocity impact damage resistance against

rocks and pebbles. It also should be resistant to various environmental challenges such as

temperature ranges, UV radiation and sand erosion. [2] [1].

26

Not only the strike face material microstructure and properties but also its interactions and

integration with the remainder (all layers) of the transparent armour system affect the

ballistic efficiency of this material. Subsequent plies are added to provide additional

resistance to penetration, and can be of the same material as the front ply. The main

purpose of thin adhesive inter-layers is to join adjacent plies or layers and also to mitigate

the stresses from potential thermal-expansion mismatch effects between the adjoining

layers. Deformation of a projectile will also increase its temperature. This interlayer will

also stop crack propagation from ceramic to polymer. [2] [10]

Parts of transparent armour systems consist of brittle materials, the fragmentation of the

ceramic and glass layers play a key role in the resistance to penetration and have been

proven to enhance the efficiency of transparent laminates against armour-piercing

ammunition significantly.

Sub-micron grain-size crystalline ceramics like AlON and Spinel appear as the preferred

material for the strike face in transparent armour systems. However on a cost/value basis it

may be more prudent to use glass ceramic materials which display structural properties

similar to those of crystalline ceramics, while maintaining lower density and the relatively

low processing cost of conventional glass. [2] [22].

Intermediate Layer

Armour systems can be engineered to provide different levels of protection by changing

variables such as the plate material, thickness of plies, interlayer hardness, interlayer

thickness, the number of plies, and the order of constituent materials. The intermediate

layer is the largest component of the three layer transparent armour system and the main

contributor to overall armour weight (Figure 5, p.25). A small outward curve in this layer

27

assists in providing the highly critical stiff backing through high bending stiffness to

support the strike-face layer. This enhances the ballistic mass efficiency of the strike-face

layer and enables the exceptionally high hardness of sub-micron grain-size crystalline to

deform and erode the projectile. [2].

As the projectile enters the intermediate layer it has been already deformed, eroded and

fragments have slowed down partially due to the stiff backing provided to the strike face.

The next objective of the material in the intermediate layer is to absorb and contain the

energy that is causing fracture from the decelerating fragments. Therefore the intermediate

layer material must be capable of high projectile kinetic energy absorption, fine scale

fracture and fragmentation toughness. The success of this layer depends on how well it

dissipates all of the bullets energy. The material has to localise crack damage and be of

sufficient density to provide multi - hit ballistic performance. It requires high optical

transparency in the visible and IR wavelength ranges and good environmental resistance to

temperature ranges and UV radiation. The use of single-ply architecture is preferred to

maximize the single-hit energy absorption capacity and reduce the transparency loss due to

the delamination effects of multi-laminates. [32].

PMMA, glass ceramics and glass are ideal materials for the intermediate layer and can

provide the needed backing support for the strike-face layer while remaining relatively

light-weight. Typically, single-ply thick panels of PMMA are used as the material for the

intermediate layer as this material has low fracture toughness and a relatively high rate of

increase of ballistic protection performance with an increase in the panel thickness. PMMA

has high elastic stiffness and high thermal, ultra-violet radiation, chemical, and scratch

resistances. Also, PMMA is amenable to a variety of processing techniques which allows

fabrication of complex transparent armour constructions. The projectile fragments and

28

ceramic or glass that is fractured by the projectile has to be contained to avoid serious

injury to personnel.

Spall Layer

While excellent in defeating ballistics, glass in particular produces debris or spall that can

be as deadly to the vehicle occupant’s survivability as the incoming threat and must be

contained. The main role of the spall or backing layer (Figure 5, P.25) is to prevent strike-

face and intermediate layer fragments from entering the vehicle cabin, while at the same

time, not undergoing spalling7 at its own back face. This layer is not expected to play a

major role in defeating the projectile but rather in the containment and confinement of the

both the projectile and transparent armour fragments. The choice of thickness in this layer

is critical. Tests have shown when spall layers were made from laminates of two 3 mm

thick PC plates, the target was able to defeat a projectile penetration. However, catastrophic

failure occurred in the glass/PC target when a 6 mm thick PC plate was used as spall layer.

(Kinloch et al., 1983 cited in [18]).

The spall layer needs highly optical transparency in the visible and IR wavelength ranges.

The material needs to be capable of projectile and armour spall containment, resistant to

temperature ranges, erosion, UV radiation, chemical warfare and highly resistant to

abrasion. Chemical and scratch resistances of this layer are important functional

requirements and the material used can be enhanced through the use of a hard chemical

resistant coating. The environmental resistances of the spall layer are also critical to insure

high durability to assist in preserving transparency after damage by enemy fire.

The most important property of the material to be used in this layer is its in-plane and

through-the-thickness ductility. The need is to provide lightweight efficient containment of

7 Spalling – splinter or break off in fragments [34].

29

the strike-face or intermediate-layer fragments and contain any back-face spalling of this

layer. PC and PU are optimal materials for transparent armour backing layer applications.

For the maximum fragment-containment capability, the backing layer should be multi-plied

and should be mechanically isolated from the intermediate layers by the use of a thicker

section of polyurethane interlayer. Armour systems can be tailored to provide for different

ballistic requirements.

Economic transparent materials will continue to be glass, acrylics and polycarbonates with

manufacturing state-of-the-art advances such as coextruded and fusion bonded materials,

stronger and tougher interlayers and continued advancement in processing methods. This

will lead to harder denser impact surface materials of superior weight ratio with advanced

environmental coatings. There will be improved spall ply concepts and materials where

smart holographic screens will control the battle field. [33].

BALLISTICS

There is no one ballistic worldwide standard, different countries and different jurisdictions

have produced charts of their individual requirements. Naturally in many cases specific

threat requirements and the test results necessary to achieve acceptance are sensitive to

each military force and therefore usually classified. Many different commercial ballistic

testing methods are used but may not always cover the wide variety of threats and range of

heavier ammunition encountered by military forces.

The U.S. Army requires ballistic testing on all vehicle types that may be deployed in a

conflict zone and military engineers are involved in vehicle design to provide maximum

protection and minimum weight. In 2008 the US Military developed a specification ATPD

2352 [36] for testing transparent armour as the ballistic threats far exceeded any of the

30

requirements outlined in available commercial specifications. [3]. The following ballistic

charts with bullet resistance material ratings are provided at Appendix ‘A’:-

UL 752

National Institute of Justice (NIJ) 018.01

State Department SD-STD-02.01

ASTM F-1233

European Standard DIN EN 1063

British Standards Institution BS 5051

Councils of Standards Australia / New Zealand AS/NZ 2343

German Deutche Institut fur Normung (DIN) 52-290

(Provided by Zbinden, L. 2014 [26])

Appendix ‘B’ (Zbinden, L. 2014 [26]) contains ballistic charts that specify the armaments

and also the material thickness for different ratings on various materials. The pdf

specification links in the last column can be assessed by Control + Click.

CONCLUSION

Military conflicts have evolved to the point where it is extremely unusual to have a defined

battle front or in some cases even a battle zone. Modern conflict and peacekeeping missions

have become a mixture of conventional and asymmetrical warfare, therefore everyone is at

risk and protection of all vehicles in the combat theatre has become a realized need.

Transparent armour has become a significant component of military effectiveness.

31

This paper has explored transparent armour systems materials and how they provide

protection in order to give the reader an overview and guidelines in selecting a suitable

transparent armour system. The challenge is to choose adequate transparent armour suitable

for the threat level from the numerous commercially available products with different

capability claims. We have seen that there are several key functional requirements placed

on the transparent armour systems used in light vehicle occupant protection. These include

single and multi-hit blast and ballistic resistance, optical clarity, non-compromise of

payload carrying capacity, environmental durability, small panel thickness to maximise

internal space, compatibility with the non-visible spectrum and high performance to cost

ratio. Transparent ceramics have been shown to reduce weight over current conventional

glass/plastic systems while increasing ballistic protection. It may be more prudent to equip

many light infantry vehicles with adequate transparent armour rather than equip a few with

advanced threat protection. It must be remembered that transparent armour is not bullet

proof but bullet resistant and will only buy valuable time for fire and manoeuvre or evasion.

32

APPENDIX A Ballistic Charts

UL 752 and NIJ I-IV

Ratings of Bullet Resistant materials as identified by: UL 752

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

Level 1 9mm Full Metal Copper Jacket with Lead Core

124 8.0 1175 1293 3

Level 2 .357 Magnum Jacketed Lead Soft Point

158 10.2 1250 1375 3

Level 3 .44 Magnum Lead Semi-Wad cutter Gas Checked

240 15.6 1350 1485 3

Level 4 .30 Calibre Rifle Lead Core Soft Point (.30-06 Calibre)

180 11.7 2540 2794 1

Level 5 7.62mm Rifle Lead Core Full Metal Copper Jacket Military Ball (.308 Calibre)

150 9.7 2750 3025 1

Level 6 9mm Full Metal Copper Jacket with Lead Core

124 8.0 1400 1540 5

Level 7 5.56mm Rifle Full Metal Copper Jacket with Lead Core (.223 Calibre)

55 3.56 3080 3383 5

Level 8 7.62mm Rifle Lead Core Full Metal Copper Jacket Military Ball (.308 Calibre)

150 9.7 2750 3025 5

Level 9 .30-06 calibre rifle, steel core, lead point filler, FMJ (APM2)

166 10.8 2715 2987 1

Level 10 .50 calibre rifle, lead core FMCJ Military Ball (M2)

709.5 45.9 2810 3091 1

Shotgun 12-Gauge Rifled Lead Slug 12-Gauge 00 Buckshot (12 pellets)

1 0z. 1.5oz

28.3 42

1585 1200

1744 1320

3 3

33

Ratings of Bullet Resistant materials as identified by: National Institute of Justice (NIJ) 018.01

Rating Ammunition Weight (grains)

Weight (grams)

Min/Max (meters/sec)

Min/Max (feet/sec)

Number of shots

Level I .22 long rifle high velocity lead

40 2.6 320 +/- 12 1050 +/- 40

5

Level I .38 special round nose lead

158 10.2 259 +/- 15 850 +/- 50

5

Level II

.357 mag. jacketed soft point

158 10.2 425 +/- 15 1395 +/- 50

5

Level II

9mm full metal jacket 124 8.0 358 +/- 12 1175 +/- 40

5

Level IIA

.357 mag. jacketed soft point

158 10.2 381 +/- 15 1250 +/- 50

5

Level IIA

9mm full metal jacket 124 8.0 332 +/- 12 1090 +/- 40

5

Level III

7.62mm (.308 Winchester) full metal jacket

150 9.7 838 +/- 15 2750 +/- 50

5

Level IIIA

.44 mag. lead semi-wadcutter gas checked

240 15.55 426 +/- 15 1400 +/- 50

5

Level IIIA

9 mm full metal jacket

124 8.0 426 +/- 15 1400 +/- 50

5

Level IV

.30-06 armour piercing

166 10.8 868 +/- 15 2850 +/- 50

1

34

Ratings of Bullet Resistant materials as identified by: State Department SD-STD-02.01

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

SD - Minimum, 9mm Parabellum

9mm Full Steel Jacket (FSJ)

115 7.45 1350 1450 3

SD - Minimum, 12 ga, 2-3/4"

12 gauge, 2-3/4", #4 Buck

556 36.03 1275 1375 1

SD -Rifle, .30, 7.62 NATO

(Part 1) .308 calibre, 7.52 NATO M80

147 9.53 2700 2800 1

SD - Rifle, .223, 5.56 NATO

(Part 2) .223 calibre, 5.56mm NATO M193

55 3.56 3135 3235 1

SD - Rifle, .223, 5.56 NATO

(Part 3) .223 calibre, 5.56mm NATO M855

63 4.08 2950 2950 +

1

SD - Rifle, 12 ga, 2-3/4"

(Part 4) 12 gauge, 2-3/4", #4 Buck

556 36.03 1275 1375 1

SD - Rifle AP, .30, 7.62 NATO

(Part 1) .30 calibre, 7.62mm NATO M61 AP

150 9.72 2700 2800 3

SD - Rifle AP, .30, 30-06

(Part 1) .30.06 calibre M2AP

165 10.69 2800 2900 3

35

Ratings of Bullet Resistant materials as identified by: ASTM F-1233

Rating Ammunition Weight (grains)

Weight (grams)

Min/Max (meters/sec)

Min/Max (feet/sec)

Number of shots

9 mm Parabellum /Submachine Gun

9mm Parabellum FMJ

124 8.04 1350 1450 3

.38 Super / Handgun

.38 Super FMJ

130 8.42 1230 1330 3

.44 Magnum / Handgun

.44 Magnum JSP

240 15.55 1400 1500 3

7.62 NATO / Rifle

7.62 mm (.308 calibre) M80 NATO

147 9.53 2750 2850 3

.30-06 Armor Piercing Rifle

.30-06 M2 AP

165 10.69 2725 2825 3

12 ga. Shotshell, 3" Magnum

12 gauge, 3" Magnum, #00 Buckshot

808 52.36 1265 1365 3

Ratings of Bullet Resistant materials as identified by: ASTM F-1233

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

Level A

.38 Special Round Nose Lead (RNL)

158 10.24 700 800 3

Level B

9mm x 19 Full Metal Jacket (FMJ)

124 8.04 1100 1180 3

Level C

.44 Magnum Full Metal Jacket (FMJ)

240 15.55 1350 1455 3

Level D

7.62mm x 51 NATO M80 147 9.53 2725 2825 3

Level E

.30-06 AP M2 165 10.69 2725 2825 3

36

Ratings of Bullet Resistant materials as identified by: European Standard DIN EN 1063

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

BR1, .22 LR .22 LR RNL 40 2.59 1048 1214 3

BR2, 9mm 9 mm Luger FSJ-RNSC

124 8.04 1280 1345 3

BR3, .357 Magnum

.357 Magnum FSJ-CNSC

158 10.24 1378 1444 3

BR4, .44 Magnum

.44 Magnum FCJ-FNSC

240 15.55 1411 1476 3

BR5, 5.56 x 45 NATO AP

5.56 mm x 45 NATO SS 109 steel penetrator

62 4.02 3084 3150 3

BR6, 7.62 x 51 NATO

7.62 mm x 51 NATO M80 FSJ

147 9.53 2690 2756 3

BR7, 7.62 x 51 NATO AP

7.62 mm x 51 NATO AP SHC

150 9.72 2657 2723 3

SG1/SG2, Shotgun

12 gauge solid lead Brenneke slug

478 30.97 1312 1444 1

Ratings of Bullet Resistant materials as identified by: British Standards Institution BS 5051

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

BSI-G0, 9 mm Parabellum

9 mm Parabellum FMJ

115 7.45 1280 1378 3

BSI-G1, .357 Magnum

.357 Magnum JSP 158 10.24 1427 1526 3

BSI-G2, .44 Magnum

.44 Magnum JSP 240 15.55 1496 1594 3

BSI-R1, .223, 5.56 NATO

.223 calibre, 5.56 mm NATO M885/SS109

63 4.08 3015 3114 3

BSI-R2, .30, 7.62

.308 calibre, 7.62 mm NATO M80

147 9.53 2674 2772 3

BSI-S86, 12ga. 2-3/4"

12 guage, 2-3/4" 438 28.38 1332 1463 1

37

Ratings of Bullet Resistant materials as identified by: Councils of Standards Australia / New Zealand AS/NZ 2343

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

G0, 9 mm Parabellum

9 mm Parabellum FMJ

115 7.45 1294 1362 3

G1, .357 Magnum

.357 Magnum SWC 158 10.24 1467 1532 3

G2, .44 Magnum

.44 Magnum SWC 240 15.55 1568 1634 3

R1, .223, 5.56 NATO

.223 calibre, 5.56 mm NATO M193

55 3.56 3182 3248 3

R2, .30, 7.62 NATO

.308 calibre, 7.62 mm NATO M80

147 7.53 2766 2831 3

S0, 12 ga, 2-3/4"

12 gauge, 2-3/4" SHOT

493 31.95 1289 1355 3

S1, 12 ga, 2-3/4"

12 gauge, 2-3/4" SLUG

382 24.75 1532 1598 2

Ratings of Bullet Resistant materials as identified by: German Deutche Institut fur Normung (DIN) 52-290

Rating Ammunition Weight (grains)

Weight (grams)

min fps

max fps

Number of shots

C1-SF and C1-SA, 9 mm Parabellum

9 mm Parabellum FMJ 124 8.04 1165 1198 3

C2-SF and C2-SA, .357 Magnum

.357 Magnum FMJ 158 10.24 1362 1394 3

C3-SF and C3-SA, .44 Magnum

.44 Magnum FMJ 240 15.55 1427 1460 3

C4-SF and C4-SA, .30, 7.62 NATO

.308 calibre, 7.62 mm NATO M80

147 9.53 2575 2608 3

C5-SF and C5-SA, .30, 7.62 NATO

.308 calibre, 7.62 mm NATO M61 AP

150 9.72 2625 2657 3

38

APPENDIX B

Bullet Resistant Glass (All Glass) - Multiple Layers of Glass and PVB

PRODUCT CODE THICKNESS WEIGHT LBS./SF

PROTECTION LEVEL SPEC PDF

UL Level 1 BR-113 1 1/4" 16.05 9mm Full Metal Copper Jacket with Lead Core

Specification Data.pdf

UL Level 2 BR-155 1 7/8" 19.51 .357 Magnum Jacketed Lead Soft Point Specification

Data.pdf

UL Level 3 BR-233 2 3/32" 26.38 .44 Magnum Lead Semi-Wadcutter Gas Checked

Specification Data.pdf

UL Level 4 BR-212 2 1/8" 27.02 .30 Calibre Rifle Lead Core Soft Point (.30-06 Calibre)

Specification Data.pdf

Secur-Tem + Poly® - Glass-Clad Polycarbonates

PRODUCT CODE THICKNESS WEIGHT LBS./SF

PROTECTION LEVEL SPEC PDF

UL Level 1 SP175 3/4" 7.84 9mm Full Metal Copper Jacket with Lead Core

Specification Data.pdf

UL Level 2 SP293 15/16" 11.11 .357 Magnum Jacketed Lead Soft Point Specification

Data.pdf

UL Level 3 SP311 1 1/8" 12.81 .44 Magnum Lead Semi-Wad cutter Gas Checked

Specification Data.pdf

UL Level 4 SP412 1 7/32" 14.5 .30 Caliber Rifle Lead Core Soft Point (.30-06 Calibre)

Specification Data.pdf

UL Level 5 SP513 1 3/8" 16.09 7.62mm Rifle Lead Core Full Metal Copper Jacket, Military Ball (.308 Calibre) One (1) Shot

Specification Data.pdf

UL Level 8 SP820 2" 22.34 7.62mm Rifle Lead Core Full Metal Copper Jacket, Military Ball (.308 Calibre) Five (5) Shots

Specification Data.pdf

NIJ Level IIA

SP175 3/4" 7.84 .357 Magnum Jacketed Lead Soft Point 9mm Full Metal Jacket

Specification Data.pdf

NIJ Level III SPN316 1 9/16" 18.39 7.62mm (308 Winchester) Full Metal Jacket Specification

Data.pdf

NIJ Level IIIA

SP412 1 7/32" 14.5 .44 Magnum Lead Semi-Wad cutter Gas Checked 9mm Full Metal Jacket

Specification Data.pdf

NIJ Level IV SPN420 2 3/16" 25.3 .30-06 Armour Piercing Specification

Data.pdf

39

Lexgard® - Laminated Polycarbonates

PRODUCT CODE THICKNESS WEIGHT LBS./SF

PROTECTION LEVEL SPEC PDF

UL Level 1 MP 750 3/4" 4.76

9mm Full Metal Jacket with Lead Core Specification

Data.pdf

UL Level 2 HP 875 7/8" 5.49

.357 Magnum Jacketed Lead Soft Point Specification

Data.pdf

UL Level 2 MP 1000 1" 6.41

.357 Magnum Jacketed Lead Soft Point Specification

Data.pdf

UL Level 3 SP-1250 1 1/4" 7.97 .44 Magnum Lead Semi-Wad cutter

Gas Checked Specification

Data.pdf

Bullet Resistant Air Gap (AG) Units - Laminated Glass Combined with Lexgard®

Laminated Polycarbonate in a Double-Glazed Unit

PRODUCT CODE THICKNESS WEIGHT LBS./SF

PROTECTION LEVEL SPEC PDF

UL Level 1 IC-1 1" 7.33 9mm Full Metal Jacket with Lead Core Specification

Data.pdf

UL Level 1 IC-

111.5 7/8" 5.65 9mm Full Metal Jacket with Lead Core

Specification Data.pdf

UL Level 2 IC-

221.5 1 1/8" 8.99 .357 Magnum Jacketed Lead Soft Point

Specification Data.pdf

UL Level 3 IC-322 1 1/4" 9.64 .44 Magnum Lead Semi-Wad cutter Gas Checked

Specification Data.pdf

UL Level 4 IC-433 1 3/4" 14.84 .30 Caliber Rifle Lead Core Soft Point (.30-06 Calibre)

Specification Data.pdf

UL Level 8 IC-862 2 1/4" 23.23 7.62mm Rifle Lead Core Full Metal Copper Jacket, Military Ball (.308 Calibre)

Specification Data.pdf

40

APPENDIX C

41

42

43

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and strategies for transparent armor systems. Materials and Design 2012; 34; 808-819.

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Bachelors’ thesis. Kettering University; December 2007.

[4] http://www.toledomuseum.org/kiosk/glass-study-interactive/exploring-glass/how-is-

glass-made/

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45

NOTES

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NOTES