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Dr S Rafi Ahmad founded and led the Centre for Applied Laser Spectroscopy (CALS) within the Department of Applied Science, Security and Resilience, Cranfield University from 1988 to 2013. He has been active for the last 3 decades in managing/supervising many R&D projects and PhD research students in the field of directed laser and applied laser spectroscopy. Dr Ahmad has authored 52 peer-reviewed publications in scientific journals, and co-authored a book with Dr Cartwright.
Preface xv
Acknowledgements xvii
1 Historical Background 1
1.1 Introduction 1
1.2 The Gunpowder Era 2
1.3 Cannons, Muskets and Rockets 2
1.3.1 Musketry 7
1.3.2 Rocketry 9
1.4 Explosive Warheads 9
1.5 Explosives Science 11
Bibliography 14
2 Review of Laser Initiation 17
2.1 Introduction 17
2.2 Initiation Processes 19
2.3 Initiation by Direct Laser Irradiation 21
2.3.1 Laser Power 21
2.3.2 Laser Pulse Duration 22
2.3.3 Absorbing Centres 22
2.3.4 Pressed Density 23
2.3.5 Strength of Confining Container 24
2.3.6 Material Ageing 25
2.3.7 Laser-Induced Electrical Response 25
2.4 Laser-Driven Flyer Plate Initiations 25
2.5 Summary and Research Rationale 27
2.5.1 Rationale for Research 28
Bibliography 29
References 29
3 Lasers and Their Characteristics 35
3.1 Definition of Laser 35
3.2 Concept of Light 36
3.3 Parameters Characterizing Light Sources 39
3.4 Basic Principle of Lasers 45
3.5 Basic Technology of Lasers 47
3.6 Comparison between Laser and Thermal Sources 48
3.7 Suitable Laser Sources for Ignition Applications 49
3.7.1 Nd:YAG Laser 50
3.7.2 Light Emitting Diodes (LEDs) 50
3.7.3 Diode Lasers 52
3.8 Beam Delivery Methods for Laser Ignition 53
3.8.1 Free Space Delivery 53
3.8.2 Fibre Optics Beam Delivery 54
3.9 Laser Safety 57
3.9.1 Laser Interaction with Biological Tissues 57
3.9.2 Precaution against Ocular Hazards 57
Bibliography 59
4 General Characteristics of Energetic Materials 61
4.1 Introduction 61
4.2 The Nature of Explosions 61
4.3 Physical and Chemical Characteristics of Explosives 63
4.4 Fuel and Oxidizer Concept 64
4.4.1 Explosive Mixtures 66
4.4.2 Pyrotechnics 69
4.4.3 Rocket Propellants 73
4.5 Explosive Compounds 74
4.5.1 Chemical Classification 74
4.6 Thermodynamics of Explosions 80
4.6.1 Oxygen Balance 82
Appendix 4.A 83
A.1 Data for Some Explosives 83
A.1.1 TNT (Trinitrotoluene) 83
A.1.2 HNS(Hexanitrostilbene) 83
A.1.3 DATB (1,3,Diamino,2,4,6,trinitrobenzene) 84
A.1.4 TATB (1,3,5,-Triamino-2,4,6-Trinitrobenzene) 84
A.1.5 Picric Acid (2,4,6,trinito- hydroxy benzene) 84
A.1.6 Styphnic Acid (2,4,6,trinito-1,3, dihydroxy benzene) 84
A.1.7 Tetryl or CE (Composition Exploding) 85
A.1.8 PICRITE (Niroguanidine) 85
A.1.9 RDX (Research Department eXplosive) 85
A.1.10 HMX (High Molecular-weight eXplosive) 85
A.1.11 EGDN (Nitroglycol) 86
A.1.12 NG (Nitroglycerine) 86
A.1.13 NC (Nitro-Cellulose) 86
A.1.14 PETN (Pentaerythritol Tetranitrate) 87
A.1.15 Metal Salts 87
A.2 Unusual Explosives 88
A.2.1 Tetrazene 88
Bibliography 89
5 Recent Developments in Explosives 91
5.1 Introduction 91
5.2 Improvements in Explosive Performance 91
5.2.1 Heat of Explosion ¿Hc (Q) 91
5.2.2 Density of Explosives 92
5.3 Areas under Development 92
5.3.1 New Requirements for Explosive Compositions 93
5.4 Plastic-Bonded High Explosives 95
5.4.1 Plastic-Bonded Compositions 95
5.4.2 Thermoplastics 96
5.4.3 Thermosetting Materials 96
5.5 Choice of High Explosive for Plastic Bonded Compositions 97
5.6 High-Energy Plastic Matrices 97
5.7 Reduced Sensitivity Explosives 99
5.8 High Positive Enthalpies of Formation Explosives 101
5.8.1 High Nitrogen-Containing Molecules 102
5.8.2 Pure Nitrogen Compounds 102
5.8.3 Other High-Nitrogen Compounds 104
5.8.4 Nitrogen Heterocycles 105
Glossary of Chemical Names for High-Melting-Point Explosives 113
Bibliography 113
References 113
6 Explosion Processes 117
6.1 Introduction 117
6.2 Burning 117
6.3 Detonation 123
6.4 Mechanism of Deflagration to Detonation Transition 124
6.5 Shock-to-Detonation 127
6.6 The Propagation of Detonation 128
6.7 Velocity of Detonation 129
6.7.1 Effect of Density of Loading 131
6.7.2 Effect of Diameter of Charge 131
6.7.3 Degree of Confinement 131
6.7.4 Effect of Strength of Detonator 132
6.8 The Measurement of Detonation Velocity 133
6.9 Classifications of Explosives and Pyrotechnics by Functions and Sensitivity 133
6.10 The Effects of High Explosives 135
6.10.1 Energy Distribution in Explosions 135
6.11 Explosive Power 137
6.12 Calculation of Q and V from Thermochemistry of Explosives 138
6.12.1 General Considerations 138
6.12.2 Energy of Decomposition 138
6.12.3 Products of the Explosion Process 139
6.13 Kistiakowsky - Wilson Rules 140
6.14 Additional Equilibria 141
6.15 Energy Released on Detonation 142
6.16 Volume of Gases Produced during Explosion 144
6.17 Explosive Power 145
6.17.1 Improving Explosives Power 146
6.18 Shockwave Effects 147
6.19 Appendices: Measurement of Velocity of Detonation 149
Appendix 6.A: Dautriche Method 149
Appendix 6.B: The Rotating Mirror Streak Camera Method 151
Appendix 6.C: The Continuous Wire Method 152
Appendix 6.D: The Event Circuit 152
Bibliography 153
References 153
7 Decomposition Processes and Initiation of Energetic Materials 155
7.1 Effect of Heat on Explosives 155
7.2 Decomposition Mechanisms 162
7.2.1 Thermal Decomposition Mechanism of TNT 163
7.2.2 Non-Aromatic Nitro Compounds 164
7.2.3 Nitro Ester Thermal Decomposition 167
7.2.4 Nitramine Thermal Decomposition 168
7.2.5 Photon-Induced Decomposition Mechanisms 169
7.3 Practical Initiation Techniques 172
7.3.1 Methods of Initiation 173
7.3.2 Direct Heating 174
7.3.3 Mechanical Methods 175
7.3.4 Electrical Systems 177
7.3.5 Chemical Reaction 177
7.3.6 Initiation by Shockwave 178
7.4 Classification of Explosives by Ease of Initiation 178
7.5 Initiatory Explosives 179
7.5.1 Primary Explosive Compounds 179
7.5.2 Primer Usage 181
7.6 Igniters and Detonators 182
7.7 Explosive Trains 183
7.7.1 Explosive Trains in Commercial Blasting 187
Bibliography 190
References 190
8 Developments in Alternative Primary Explosives 193
8.1 Safe Handling of Novel Primers 193
8.2 Introduction 193
8.3 Totally Organic 194
8.4 Simple Salts of Organics 199
8.5 Transition Metal Complexes and Salts 202
8.6 Enhancement of Laser Sensitivity 206
References 207
Appendix 8.A: Properties of Novel Primer Explosives 211
Appendix 8.B: Molecular Structures of Some New Primer Compounds 213
Purely Organic Primers 213
9 Optical and Thermal Properties of Energetic Materials 221
9.1 Optical Properties 221
9.1.1 Introduction 221
9.1.2 Theoretical Considerations 222
9.1.3 Practical Considerations 225
9.1.4 Examples of Absorption Spectra 226
9.2 Thermal Properties 231
9.2.1 Introduction 231
9.2.2 Heat Capacity 232
9.2.3 Thermal Conductivity 232
9.2.4 Thermal Diffusivity 233
References 234
10 Theoretical Aspects of Laser Interaction with Energetic Materials 235
10.1 Introduction 235
10.2 Parameters Relevant to Laser Interaction 236
10.2.1 Laser Parameters 236
10.2.2 Material Parameters 236
10.3 Mathematical Formalism 237
10.3.1 Basic Concept 237
10.3.2 Optical Absorption 238
10.3.3 Optical Reflection 240
10.4 Heat Transfer Theory 240
References 245
11 Laser Ignition - Practical Considerations 247
11.1 Introduction 247
11.1.1 Laser Source 248
11.1.2 Beam Delivery System 249
11.2 Laser Driven Flyer Plate 249
11.3 Direct Laser Ignition 250
11.3.1 Explosives 251
11.3.2 Propellants 259
11.3.3 LI of Pyrotechnic Materials 263
References 267
12 Conclusions and Future Prospect 269
12.1 Introduction 269
12.2 Theoretical Considerations 269
12.3 Lasers 270
12.4 Optical and Thermal Properties of Energetic Materials 271
12.5 State of the Art: Laser Ignition 271
12.6 Future Prospect 272
References 274
Index 275
Historically, mankind has tried to dominate both fellow human beings and other animals for as long as humans have been around. Some of this domination was achieved by killing other species. This had two aspects; survival and providing food.
Survival was dictated by the fact that many animals regarded humans as excellent sources of food and were quite capable of killing humans. Humans could have two approaches; avoid areas known to contain threatening species or produce devices – weapons – which would enable humans to kill the threatening animals. Humans then developed a taste for the flesh of some of the animals they had killed, thus increasing the sources of food available. As the human population increased, conflict between humans for food and territory increased, and so humans started to fight amongst themselves. By using weapons, humans could overcome physical disadvantages, and the optimum situation was to be able to kill your opponent before they could kill you.
The sword and lance effectively extended the human arm and kept your opponent at bay but, as lances became longer and longer, they became more unwieldy. A remote killing weapon was required. Simple javelins, which could be thrown at the opposition, extended the distance between opponents but required considerable physical stature and skill to achieve the correct flight trajectory for the javelin. Therefore, in order to overcome human physical limitations, mechanical advantage devices were used. The earliest weapons for remote killing were simple slings. These could carry a stone and were capable of accelerating it to high velocity by spinning the sling in a circle. When one of the supporting thongs was released, the stone would travel in an almost straight line from the point of release. Impact of the stone with an animal or human was capable of killing or injuring the animal.
With the development of wood manufacturing skills, bows and arrows became individual weapons or, when grouped together became a lethal hail of arrows which did not depend on the individual accuracy of the archer. The longbow was the ultimate in these weapons. Improved performance came when mankind developed stored energy devices, such as the ballista and crossbows, both of which stored mechanical energy in wooden elements but required winding up before loading the stone or arrow projectile. These overcame the limitations of physical stature required to effectively use the longbow. The ballista, Figure 1.1, was also used to fire barrels of burning oil at the enemy when they had formed shield walls against arrows. The oil container burst on impact and was one of the first deployments of pyrotechnics weapons.
Figure 1.1 Small-scale basic ballista. Reproduced with permission from Cranfield University © 2014.
Meanwhile, the Chinese were developing the first chemical explosive gunpowder. The earliest record of this was around 800 AD. Initially, the mixture was for use as a medicine but, as with all good inventions, serendipity intervened and a batch of the medicine fell on to the fire over which it was been cooked; it very rapidly burnt with a flash, smoke and rushing sound. The potential for this was recognized, and the Chinese started to use the mixture as a propellant for their lances/javelins. When attached to the normal throwing spear, these early rockets could extend the useful range of the javelin by as much as a factor of two.
It took about 400 years for the technology to appear in Europe, when a cleric Roger Bacon was credited with discovering the properties of gunpowder. He was so afraid of its properties that he hid the details of the composition in code in religious manuscripts. The recognition of its propellant properties resulted in the manufacture of muzzle-loaded cannons.
An idea of the chronology of the development of the science is given in Table 1.1 on page 3.
Table 1.1 Some significant discoveries in the history of explosives.
1 Explosive properties of Picric acid were not investigated for a further 100 years.
2 Pelouze produced NC but did not understand the chemistry whereas Schonbein correctly identified the chemistry and made some propellant uses.
3 Schultze produced the first successful powdered NC propellants and Vielle was credited with the first NC propellants for rifled barrel guns.
The barrels of the first cannon systems were simple wooden devices made from hollowed-out tree trunks, which were wrapped with wet ropes for added strength. The development of bronze and cast iron technology led to the production of iron-barrelled guns, such as the Bombard, used at the battle of Crecy in 1346 (shown in Figure 1.2). This weapon used solid projectiles in the form of either suitable stone or cast metal (e.g. iron) spheres. The development of these weapons resulted in the foundation of the Board of Ordinance in 1414. The operators of these weapons were known as Bombardiers – a term still used for an artilleryman with the rank of corporal in the British Army.
In the fifteenth century, cannon were also deployed at sea on warships and these enabled the opposition to be destroyed at distance without needing to engage in hand to hand combat. A number of cannons were deployed along each side of the ship, and a broadside could be loosed at the opposition. Typical cannons are shown in Figure 1.3, which displays a typical army cannon in the foreground and a naval cannon in the background.
Figure 1.2 Crecy bombard 1346. Reproduced with permission from Cranfield University © 2014.
The naval cannon was mounted on a four-wheeled trolley rather than the two wheels of the army. This provided better stability onboard a ship in heavy seas. The iron guns were made of a number of staves, or bars, of iron which were formed into a cylinder around a mandrel. Collars and hoops of wrought iron were heated and slipped over the cylinder. As these cooled, they contracted to form a reinforced tube. Surprisingly, breech-loaded cannon (often regarded as a modern invention, introduced when screw cutting technology was developed during the Industrial Revolution) were available in the early fifteenth century. The early systems used a simple hollow steel tube mounted on a wooden trough, with a space between the end of the metal tube and the end of the wooden support. A closed metal cup containing the propellant charge was then inserted into the gap and rammed into the rear open end of the barrel. The system was then sealed by inserting a wooden plug behind the...
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