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Woodhead Publishing in Materials

The Science of Armour

Materials

Edited by

Ian G. Crouch

AMSTERDAM • BOSTON • CAMBRIDGE • HEIDELBERG

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List of contributors

L. Arnold RMIT University, Brunswick, Victoria, Australia

H. Billon Defence Science and Technology Group, Fishmermans Bend, Victoria,
Australia
S.J. Cimpoeru Defence Science and Technology Group, Fishermans Bend,
Victoria, Australia
I.G. Crouch RMIT University, Brunswick, Victoria, Australia; Armour Solutions
Pty Ltd, Trentham, Victoria, Australia
D.P. Edwards Defence Science and Technology Group, Fishermans Bend, Victoria,
Australia
L. Edwards ANSTO, Lucas Heights, NSW, Australia
B. Eu Ballistic and Mechanical Testing, Port Melbourne, Victoria, Australia
G.V. Franks The University of Melbourne, Victoria, Australia
M.A. Kariem Bandung Institute of Technology, Bandung, West Java, Indonesia
H. Li University of Wollongong, NSW, Australia
M. Naebe Deakin University, Waurn Ponds, Victoria, Australia
A. Pierlot CSIRO, Waurn Ponds, Victoria, Australia
D. Ruan Swinburne University of Technology, Hawthorn, Victoria, Australia
S. Ryan Defence Science and Technology Group, Fishermans Bend, Victoria,
Australia
M. Saleh ANSTO, Lucas Heights, NSW, Australia
J. Sandlin DMTC, Hawthorn, Victoria, Australia
D. Shanmugam Thales, Bendigo, Victoria, Australia
C. Tallon Virginia Tech, Blacksburg, VA, United States
S. Thomas Defendtex, Dandenong South, Victoria, Australia
Introduction

In 2009, the Defence Materials Technology Centre (DMTC) was in its establishment
phase. Founded by a leading group of Australian research and industry sector players,
DMTC represented e and represents e a significant initiative on the part of the sector
to consolidate a broad range of high-technology activities and focus outcomes on
improving Australian defence capability. The organization had an established pro-
gramme aimed at the protection of land vehicles and the beginnings of a programme
aimed at protection of dismounted personnel.
My diary is always close to full.
In a good week, there might be two or three blocks of a couple of hours unfilled by
meetings and appointments and I have an excellent EA who diligently works to keep
things moving. It can be a challenge to fit everything in and appointments with some
people often needing to give way some or all of the time to pressing schedules. Not so
for Ian Crouch, who I had known for several years and who was always consistent in
his passion and belief that we could do things better. His ‘we can do this’ attitude has
always been so important and I very much looked forward to our meetings. We met as
planned. I’m so glad we did.
As an engineer myself and the leader of the centre, I was of course aware of some of
the nascent and established capabilities in the Australian armour and protective tech-
nologies arena, but Ian who had been a leading light for some years, was able to outline
the true extent of the environment with great authority and his usual wit, passion and
charm. The story of Australian armour and protective technologies both before and
since the advent of the DMTC encompasses a narrative of persistence and excellence.
Characterised by largely self-contained, short supply-chains with low production runs
and a liberal helping of uncertainty, life can be challenging for industrialists in this
sector. Ian and many of his colleagues from industry and research were significant
drivers of the effort to stand up a programme of technologies that brought together
a suite of armour and protective technologies in the mounted/vehicles and dis-
mounted/personnel domains, and deliver these to a very demanding customer with,
appropriately, little tolerance for second best.
These efforts and successes arising therefrom have been lauded in many fora, and
most importantly have been acknowledged as saving lives by the Australian Army.
Surely there can be no more worthy pursuit for innovators.
Success is, of course, a very confused being with regard to claims against its true
parentage, but as one who has been close to the action for the past decade, I can attest
to the central role Ian played in developing and championing the technologies and ca-
pabilities presented herewith. Many others have also made significant contributions to
xii Introduction

this body of knowledge, experience and expertise, that have given Australian and
allied personnel the confidence in their protective equipment ensembles. Some of
the authors in this publication have the passing privilege of youth.others (who I’m
confident will not mind me pointing out) bring experience to the table.
Ian Crouch manages both qualities, and has spearheaded the development of this
significant body of work in, by and for the benefit of Australia and its allies. This has
been e in the spirit embodied by the DMTC and its many partner organisations e a
true collaborative effort and a proudly all-Australian initiative which we present for
your consideration.

Dr Mark Hodge
Chief Executive Officer
Defence Materials Technology Centre
Australia
Foreword

For the first half of 2009 I was responsible for the effective employment and protection
of all Australians in Afghanistan. The men and women under my command had a
mixture of body armour, none of which in my opinion was entirely suitable for the
work they were doing and most of it was most certainly inferior to that which many
of our coalition partners’ soldiers were wearing. In my view the Australian ’modular
combat body armour system’ did little more than turn a soldier into a ‘pillbox’. There
appeared to be a lack of appreciation in its development that a significant component of
a soldier’s protection was the ability to fire a weapon and to move quickly, in addition to
physical protection. If a soldier did nothing more than wear all the issued body armour,
he or she was carrying almost as much weight as any Australian soldier in history before
even considering the weight of ammunition, water and rations. It was at this point
I became fascinated with the technologies and functionality of body armour.
My chance came to do something about it when I returned from Afghanistan.
I returned to Army Headquarters on promotion as the inaugural Head of Modernisation
and Strategic Planning. Then, to make my mission of fixing the situation more urgent,
in the Senate Estimates hearing after I returned in 2009, the Chief of Army was asked
to explain the very significant number of complaints by soldiers and their concerned
parents about the lack of utility of the personal load carrying and protective equipment
issued to soldiers, especially the weight and physical restriction imposed by the body
armour.
In late 2009, I met Dr Ian Crouch and found in him someone able to answer all of
my questions about the weight versus protection dilemma; and someone who would be
a great help to me to do something about it. Together, after a meeting at Australian
Defence Apparel (ADA) in Bendigo, we started the journey to get our soldiers better
protection on combat operations. He had the technical expertise and I had the author-
ity. Before we had left the factory floor we had established what was feasible, accept-
able and suitable, how long that would take and what the major issues were.
Almost two years to the day after that meeting with Ian, I was very proud to visit
the battle group training in Townsville, which was readying for deployment to
Afghanistan. The commanding officer was ecstatic with the result and we could not
find one soldier who was not likewise impressed with his new equipment issue.
What became known as T-BAS (Tiered Body Armour System) incorporated the new
body armour and an innovative combat load-carrying equipment solution. All of this
was pursued and coordinated by ’Diggerworks’, an organisation raised as a collabora-
tion in Defence to lead and stay at the front of developments in soldier personal
xiv Foreword

equipment. The Defence personnel who became the engine room of Diggerworks were
the architects of the first TBAS design and drivers of its user-centred iteration that made
TBAS the truly fit-for-purpose system of which we are all justifiably proud.
Every soldier, their families and their commanders on combat operations owe a debt
of gratitude to Ian and his team for their work in fixing this problem in quick order.
There is no doubt we saved lives as a consequence. We achieved this through Ian’s
intimate knowledge of armour materials combined with a shared understanding of
an infantryman’s approach to the optimal balance between weight, fit and protection
that enabled effective fire and movement. The current design is a significant step
change from MCBAS.
This book is a testament to the knowledge and enthusiasm of Dr Ian Crouch. It is
people like him and those who will gain from this book that can have a significant
impact on the lives of our service personnel. I am eternally grateful for what Dr Ian
Crouch has done for us already and what he continues to do in publications such
as this.

Lt Gen John Caligari, AO, DSC (Rtd),

Chief of Capability Development Group to August 2015

Ministers Warren Snowden and Jason Clare, together with Lt Gen John Caligari, at the official
opening of the DMTC’s Boron Carbide Pilot Plant in March 2011.
Preface

I am proud to present this new work on armour materials for I believe that it is the first
truly materials-focused book on armour in more than 40 years. It is comprehensive in
its treatment of the international literature and its coverage of recent technological ad-
vances. To its credit, it is also coherent in its treatment of the interdependence of the
various material groups, with numerous cross-references between individual chapters.
The idea of compiling such a book came to me during 2010, as I was finishing up my
career with Australian Defence Apparel, supplier of body armour systems to the
Australian Defence Force. I realised then what a charmed working life I had been fortu-
nate to experience; one that started in the UK, within the defence research organisations,
followed by 20 years in Australia with a number of defence industrial companies.
Throughout this time, since 1980, I have been intimately involved in the international
armour community, either as a researcher, armour technologist, or as someone pushing
to commercialise new armour materials and systems. This book contains many extracts,
incidents and armour materials downloaded from those various experiences. It also
reflects the collaborative nature of my most recent activities, working as a Project
Leader within the Defence Materials Technology Centre (DMTC) in Australia, since
all of my fellow coauthors are participating researchers within that centre. The
Australian armour community has certainly expanded during the past 10 years or so.
The book itself has been written primarily for the early practitioner since I had no
such textbook back in the 1980s when I was learning my craft. It is structured along the
lines of a conventional materials engineering textbook, covering all major families of
materials. Each chapter covers one group of armour materials, treating each group as a
specialised subset of the broader set of engineering materials, from the well-
established armour steels, through the families of light alloys, to the designer armours
involving ceramics, textiles and composites. The material science behind each family
of armour material is treated in great detail: energy-absorbing mechanisms are well
covered, as are the various penetration modes, since understanding these failure mech-
anisms is at the heart of developing new armour materials. As mentioned at the begin-
ning of Chapter 1, the science of armour materials is not a codified branch of
engineering e it is a science in its own right e a science based around the high-
strain-rate properties of materials and localised deformation behaviour. Each of the
chapters contains summary tables of key properties providing an excellent source of
reference material and ballistic data. One of the major themes running through the
book is the design of real armour systems: the principles and guidelines used to design
xvi Preface

not only simple, elemental systems but also multilayered structures, like the ceramic-
faced composite armours. Many examples of real-life case studies are provided.
Chapter 1 commences by considering the operational environment as well as detailing
the threat, since this is always the first thing to consider when designing or developing an
armour system. For a number of reasons, the threat spectrum has been limited to small
arms ammunition, high-velocity fragments, knife and spike attacks, and various blast
loadings. The introductory chapter also includes essential background reading for the
nonmaterial scientist and some revision notes for the more experienced researcher.
Two chapters follow it on traditional armour materials, namely the family of armour
steels in Chapter 2, and the group of light alloys, covered in Chapter 3. Both chapters pro-
vide sound metallurgical background information and key points about these traditional
armours, their engineering properties and comparable joining techniques. Most of them
are structural in nature and, whilst the steels are close to the end of their research and
development phase, after more than 100 years, they are still the material of choice for
most armoured military platforms. They may also still have a role to play in future
body armour systems. Titanium alloys certainly have a role to play in protection against
small arms ammunition, as do the high-strength grades of aluminium alloys.
Chapter 4 is very much a transition chapter between the traditional, monolithic,
metallic armours in Chapter 2 (Steels) and Chapter 3 (Light Alloys) and the ‘designer
armours’ covered in later chapters. It provides an insightful review of laminated mate-
rials and layered structures, recognising that the most efficient armour materials have
a lamellar, laminated or layered structure. Key properties of a laminate are elucidated:
their crack-arresting behaviour, as well as the essential role of interfaces and interlayer
materials. The chapter makes essential reading before considering the laminated fibre-
reinforced structures in Chapter 5 (Polymers and Fibre-Reinforced Plastics), the layered,
textile structures of Chapter 6 (Fires, Textiles and Protective Apparel) and the ceramic-
composite armours covered in Chapter 7 (Glasses and Ceramics).
Chapter 5 introduces the range of both reinforced and unreinforced polymers and in-
cludes a comprehensive review of the many methods of manufacturing armour-quality,
composite components. This is an important topic since each approach results in an armour
product with very different properties. The chapter also introduces the new wave of
spliceless technologies that enable fully formed combat helmet shells to be manufactured
in one step from a flat, lay-up of composite materials, especially those based upon
advanced materials like the ultrahigh-molecular-weight polyethylene (UHMWPE) fibres.
In Chapter 6, the theme of layered armour materials is continued by introducing the
reader to the science behind soft armour vests that can stop not only handgun bullets
but also knife and spike threats. Each constituent of the vest is considered in turn, from
the constitution of the fibres, and the structures of both woven and nonwoven fabrics,
to the stitched layers of dry fabrics and finally to the shaping of the vest itself. The vari-
ables within each element are detailed, as well as the various energy-absorbing mech-
anisms, and, as stated above, many tables of relevant properties and characteristics
accompany these. Stopping a knife from penetrating the human body is as challenging
as defeating a handgun bullet.
Glasses and ceramics are, in my opinion, the most important family of armour ma-
terials, and Chapter 7 covers this highly developed group in some detail. The trans-
parent ceramics, evolving steadily to replace the poorer-performing float glasses are
Preface xvii

reviewed, and manufacturing methods compared. However, most attention is given to

the high-performance opaque ceramics, like the aluminas and the carbides of both sil-
icon and boron, which have the highest ballistic merit ratings, certainly in terms of
weight. Regularly used as key elements of a body armour system, particular attention
is given to describing reaction sintered/bonded products and a newly developed pro-
cess based upon viscous ceramic processing which, in combination with pressureless
sintering, has been developed by the DMTC to produce thin, shapeable, armour-grade,
boron carbide products.
Whilst computers, or numerical modellers, do not design armour systems per se,
their role within the science of armour materials is well established. Two, standalone
chapters are dedicated to these mathematical approaches. Chapter 8 presents a very
comprehensive review of analytical techniques. Written by one of Australia’s leading
defence scientists, Dr Shannon Ryan, it covers various formulations to calculate crit-
ical penetration limits of armour materials and systems. From simple models based
upon quasistatic work done to sophisticated algorithms based upon either semiempir-
ical or fundamental physical relationships, these mathematical tools enable the armour
technologist to estimate/predict ballistic performance without having to carry out
expensive and/or time-consuming ballistic experiments. Chapter 9, on numerical
modelling techniques, is equally comprehensive. The largest chapter in the book, it in-
troduces the basic physics behind these nonlinear, finite element computer codes, by
covering most armour materials and including many worked examples. A gamut of
armour/antiarmour interactions is focused upon impacts from either small arms ammu-
nition or high-velocity fragments. However, the real power of computer simulations is
their ability to simulate a specific failure mode or defeat mechanism, and thereby raise
our understanding of the science involved. Chapter 9 also includes a very useful colla-
tion of standard input parameters for the various strength models or underpinning
equations of state e essential data when starting out in numerical modelling.
Input data for the above-mentioned mathematical formulae are normally generated
via dedicated high-strain-rate tests, such as the well-known split Hopkinson pressure
bar (SHPB). Chapter 10 describes these test procedures in detail, as well as a number
of selected, quasistatic tests that have been used to simulate a particular failure mech-
anism. For example, armour materials can absorb a considerable amount of impact en-
ergy in the through-thickness (TT) direction. But, rather than carrying out a standard
TT compression test on a simple cylinder of test material, it is preferable, and far more
relevant to an armour impact, to perform the test using a constrained compression test
(CCT). Chapter 10 provides details of this test, as well as the standard range of high-
strain-rate methods including plate impact, fragmentation, and spallation tests.
The lay reader may find that one of the most useful chapters in this book is Chapter
11 on Ballistic Testing Methodologies. It provides a brief overview of the scientific
principles and engineering objectives behind a ballistic test. Written by two authors
who, between them, have more than 40 years experience in ballistic testing, it presents
a broad suite of tests which can be adopted by researchers at the outset of an armour
program, or by engineers when accurately validating their preferred armour system, or
by ballistic testing staff when carrying out certification tests. Commentary about the
well-known, but poorly understood, ‘V-50’ test is particularly insightful.
xviii Preface

The book concludes by taking a visionary look at the future of armour materials.
Whilst research into steels may have run its course, exciting new developments in
transparent ceramics, 3D printed structures, and graphene-reinforced interlayers, for
example, ensure that even better armour materials are yet to be developed. However,
driving down the manufacturing costs of these specialist materials is just as important
as continuing to improve their ballistic properties. In Chapter 12, therefore, a new
approach to selecting targeted groups is proposed, based upon a quantitative cost-
benefit analysis.
Finally, I need to thank all of those people who have contributed not only to this work
but also to my career. To my fellow coauthors, I am indebted to you for all of your dedi-
cated efforts e without you this book would not have been the same. I am particularly
grateful to Dr Stephen Cimpoeru, Dr Shannon Ryan and Horace Billon, from the Defence
Science and Technology Group, as well as James Sandlin from the DMTC. To my spon-
sors, Armour Solutions Pty Ltd and the Defence Materials Technology Centre, I thank
them for their financial support. I am especially grateful to Dr Mark Hodge, CEO of
the DMTC, who has always shared the same vision, on many topics. Across my long
career, there are three people who have inspired me and supported me: Dr Neill Griffiths,
Head of the Armour/Anti-Armour Group at DRA, in the 1980s; Dr Bill Carson, Head of
the Armour Physics division at DERA, in the 1990s, and finally Brian Rush (pictured
below), owner of Australian Defence Apparel (1995e2011), whose visionary outlook,
and willingness to spend the R&D dollar, ensured that Australia developed a new suite
of armour technologies during the past 20 years.

Defence Minister Joel Fitzgibbon (c.2008), with Brian Rush, Managing Director of ADA, and
Dr Ian Crouch, during a visit to ADA, Bendigo, during the production of the Modular Combat
Body Armour System, supplied to the Australian Defence Forces.
Preface xix

Success, in any field, is about understanding, and overcoming, failure, and in the
field of armour materials it is about understanding the penetration failure mechanisms
associated with different forms of attack. Following this Preface is a poignant piece of
poetry for the professional engineer responsible for ensuring that material failures do
not occur. Enjoy the poem, and the book!

Dr Ian G. Crouch, Managing Director (Armour Solutions Pty Ltd), Adjunct

Professor (RMIT University, Melbourne), and Project Leader (Defence Materials
Technology Centre, Australia)
Forethought

Hymn of Breaking Strain (1935) by Rudyard Kipling (AD 1865e1936)

The careful text-books measure

(Let all who build beware!)
The load, the shock, the pressure
Material can bear.
So, when the buckled girder
Lets down the grinding span,
The blame of loss, or murder,
Is laid upon the man.
Not of the Stuff e the Man!
But, in our daily dealing
With stone and steel, we find
The Gods have no such feeling
Of justice toward mankind.
To no set gauge they make us, e
For no laid course prepare e
And presently o’ertake us
With loads we cannot bear:
Too merciless to bear.

The prudent text-books give it

In tables at the end e
The stress that shears a rivet
Or makes a tie-bar bend e
What traffic wrecks macadam e
What concrete should endure e
But we, poor Sons of Adam,
Have no such literature,
To warn us or make sure!
We hold all Earth to plunder e
All Time and Space as well e
Too wonder-stale to wonder
At each new miracle;
Till in the mid-illusion
xxii Forethought

Of Godhead ’neath our hand,

Falls multiple confusion
On all we did or planned e
The mighty works we planned.

We only of Creation
(Oh, luckier bridge and rail!)
Abide the twin-damnation e
To fail and know we fail.
Yet we e by which sole token
We know we once were Gods e
Take shame in being broken
However great the odds e
The Burden or the Odds.

Oh, veiled and secret Power

Whose paths we seek in vain,
Be with us in our hour
Of overthrow and pain;
That we e by which sure token
We know Thy ways are true e
In spite of being broken,
Because of being broken,
May rise and build anew.
Stand up and build anew!
Introduction to armour materials
I.G. Crouch
1
Armour Solutions Pty Ltd, Trentham, Victoria, Australia

The design and application of armour is a science rather than a codified branch of en-
gineering. Whilst all professional engineers follow sound engineering principles and
practice, I suspect that some might mistakenly believe that the application of the engi-
neering process is all that is required for optimised, risk-free armour solutions, like
choosing the optimum tyre for a car based upon the conduct of standardised tyre
testing. The science of armour materials is a specialised, cross-disciplinary subject
not taught within the educational system and most armour technologists, like me, learn
on the job. To begin to understand the underpinning science we must first consider the
operational environment and then, most importantly, the threat.

1.1 The operational environment

Imagine yourself in the middle of a war zone or, as the military like to call it, a theatre
of operation, somewhere in the Middle East. Whether it is a location like Iraq, or
Afghanistan, during the period 2003e14, these battlefields are dangerous, chaotic en-
vironments where many random explosions, or high-energy impact events, occur on a
regular basis. This is the environment that armour materials have to function in, and
function reliably, as there is minimal margin for error (Fig. 1.1).
For the Australian Defence Force (ADF), fighting these ground-based wars has
proven to be very costly, with 41 Australian fatalities occurring during the 10-year con-
flict in Afghanistan; not forgetting, of course, the many thousands of civilian and mili-
tary lives lost from other nations. As Chris Masters reports in his recent account of the
life of a serving soldier on active duty in Uruzgan province (Masters, 2012), from bases
like Tarin Kowt, this environment is dusty, hot (during the day), cold (at night), even
snowy (during the winter) and very rugged. Extremely harsh conditions for the soldier:
extremely harsh conditions for the equipment, and therefore very challenging for the en-
gineering materials. For example, the rapidly rotating blades of the Blackhawk helicop-
ter, constructed from relatively soft, carbon-fibre reinforced plastic, need to withstand
the grinding action of the dusty, sandy conditions. The pilots need to feel protected
from small-arms fire coming up from the ground. Troopers in their armoured vehicles
like the Bushmaster, an Australian protected mobility vehicle, need to feel protected
from random explosions coming from improvised explosive devices (IEDs) and land-
mines, and survive. The combatants on the ground, chasing the Taliban across the
open plains, need to feel fully protected wearing their latest body armour, as well as
comfortable and mobile.

The Science of Armour Materials. http://dx.doi.org/10.1016/B978-0-08-100704-4.00001-3

Copyright © 2017 Elsevier Ltd. All rights reserved.
2 The Science of Armour Materials

Figure 1.1 Range of materiel and armour materials in active service, 2012.
Anon, 2012. Australian Department of Defence Website. www.defence.gov.au.

Consider for a moment the armour materials that are also present on these same bat-
tlefields. Lightweight, aluminium alloys, forming the helicopter structures, with ultra-
lightweight ceramic armour on the underside of the pilot’s seat. A range of weldable,
high-strength steels act as structural armours in the Bushmaster vehicles. However,
which grades of steel are being used, and why? Thick-sectioned, weldable, aluminium
alloys which form the box-like structures of the fleet of up-armoured M113s (an arm-
oured personnel carrier, APC); vehicles which have remained in active service for the
past 50 years. What about the range of materials that make up the modern-day body ar-
mour system (BAS)? These can be the most complex passive armour systems on the
battlefield and traditionally include a Kevlar vest, as well as a hard armour plate
(HAP) to provide additional protection against high-velocity rifle rounds, like the
AK47 bullets, fired from Kalashnikov rifles.
Such BASs do save lives! Take the case of Lance Sergeant Collins of the 1st
Battalion of the Welsh Guards who was on a tour of duty in Afghanistan during
2009. He and his company had been under sporadic fire during a day’s clearance oper-
ation (Anon, 2009). ‘I knelt down in an irrigation ditch in partial cover when I was hit
in the back by a single shot. It must have been from about 200 to 300 metres away’, he
said. In describing his near-death experience, Collins said, ‘The round knocked me
down in an instant. It felt like being hit by a sledge-hammer at full swing. I slammed
into the dirt, face down’. Fig. 1.2 not only shows the damage to his body armour but
also to his back e the HAP had done its job and Collins survived to fight another day.
Introduction to armour materials 3

Figure 1.2 Survivor, Lance Sergeant Collins (1st Battalion, Welsh Guards) with his damaged
body armour system and bruised back.
Anon, 2009. Shot Soldier’s Body Armour Praise. http://www.dailymail.co.uk/news/article-
1191872/Soldier-snipers-bullet-pulled-comrade-shot-Taliban.html.

These HAPs are highly engineered products, finely tuned to offer maximum protec-
tion for minimum weight, but which grade of ceramic is best to use in this application?
Fig. 1.3 shows a schematic of a section through such a BAS and the full range of ar-
mour materials that are considered when designing such systems, especially the HAP.

Soft armour insert: layers of aramid or UHMWPE

Hard armour plate:

Strike face material: UHHS, Al2O3, SiC, B4C

Substrate support: CFRP, etc.

Backing materials: GFRP, KFRP, UHMWPE

Impact protector: rubber, foam, etc.

Adhesives:various

Covers:ballistic nylon, rubber, etc.

Edging strips: rubber or aluminium

Figure 1.3 Cross-section through a typical body armour system.

Crouch, I.G., 2009. Threat defeating mechanisms in body armour systems. Paper Presented at
the Next Generation Body Armour, London, September 2009.
4 The Science of Armour Materials

How do all of these armour materials (the steels, the aluminium alloys, as well as
the ceramic materials in the HAPs) get qualified for use in such demanding roles? Ima-
gine the training, history and the processes that armour designers and engineers have
had to go through in order to develop, produce and approve the use of such materials in
these hostile environments. Like any other field of science, or engineering, the armour
technologist needs to simplify the real situation and design for the worst-case sce-
narios. In this case, this means developing an armour system, which can stop the pre-
scribed threat (eg, a steel-cored bullet) at a specified velocity and obliquity. Designing,
and/or selecting, the most appropriate material to best suit an engineering application
is, of course, what practicing material scientists and design engineers do, as a conven-
tional part of their profession. So, what makes working with armour materials so
different and the science of armour materials so exciting?
From a material science perspective, imagine a typical impact event: the impact of a
steel-cored bullet, travelling at many hundreds of metres a second, striking the steel
armour on the side of an armoured vehicle. Consider the step-by-step series of physical
events that follow. Do not forget that the entire impact event will be completed within
100 ms or so.
• Upon impact, a series of stress waves are induced within the material, and travel throughout
the structure. These waves travel at the speed of sound, within the material, which, in the case
of steel structures, is almost 6,000 m/s. Since these waves are travelling much faster than the
bullet, do they cause any changes in the material, ahead of the bullet, which might affect the
subsequent behaviour of that material?
• If the armour system has been designed correctly, there will be a period of dwell, where the
bullet is deformed at, or near, the surface of the steel, without penetrating the armour. How
much deformation occurs to the bullet? Will it be eroded or plastically deformed? Will it sim-
ply ricochet off?
• Once the bullet starts to penetrate the armour, the material needs to flow, as it would in a
hardness test, where a diamond tip is forced into the surface of the material. However, unlike
a hardness test, this penetration process occurs dynamically. How does the material flow un-
der these extreme conditions of high strain rates, high temperatures and high local pressures?
How will the material resist this momentous force, and how can a material scientist best
describe this complex flow behaviour? Can analytical or numerical modelling help?
• As the bullet is arrested, and the strain-rate decreases, the rear side of the armour will start to
experience the full force of the impact event and be stretched to the limit. Literally, in some
cases. How might the material fail? Locally? Globally? Will the steel structure be deformed?
These questions, and many others, will be analysed in the coming sections and
chapters. The rest of this introductory chapter focuses upon the fundamentals of ar-
mour materials and the design principles behind the development of lightweight ar-
mour systems.

1.2 The threat

The most challenging task in developing a particular armour material, or system, is
analysis of the real, or perceived, threat and the generation of incident data that are
Introduction to armour materials 5

both accurate and current. This approach is vital because there is not a single armour
system available that is the best armour for all types of threat. This is especially true for
soft armours where different sets of high-performance fabrics (eg, Kevlar) are required
for stab and spike threats compared with, say, handgun bullets. Both Brady (2003) and
Horsfall (2009) have compiled lists of military casualties by war and by threat type.
For example, in the Gulf War, like WW2, many more casualties occurred as a result
of impacts from high-velocity fragments compared with bullets. However, in Borneo,
90% of casualties arose from bullet strikes. In recent conflicts, like those theatres of
operation in Afghanistan and Iraq, the major cause of fatalities and casualties has
been from the IED, not small arms ammunition (Kelly et al., 2008). In fact, Kelly re-
ported a significant change in the threat spectrum, with IED threats becoming domi-
nant in the 2 years from 2004 to 2006. Since then, in military campaigns involving
terrorist activities, IEDs have become the major threat.
In Australia, the Department of Defence has taken a direct approach in relaying the
real demands of the dismounted soldier by forming an organisation called Digger-
works in 2010 (Cebon and Samson, 2010). Its purpose is to steer research and rapid
development, based upon first-hand military experience e its first Director was
Colonel Jason Blain who had led an Australian battalion in Afghanistan the previous
year. Diggerworks, DSTO (now the DST Group) and the Defence Materials Technol-
ogy Centre (DMTC), have been working in closer collaboration ever since.
In the civilian world, handguns and rifles are still the weapon of choice in the
Americas, whilst in Europe, and especially the major cities like London, knife and
spike attacks dominate. Paul Fenne, from the technical department of the London
Metropolitan Police reported (Fenne, 2008, 2009) that the total number of violent
crimes in London had reached 13,000 per annum and that, in 2009, armed response
units responded to 11,725 calls. Of these, 2232 calls required specific deployment
of armed police wearing body armour.
In general, textbooks that cover armour/antiarmour interactions normally divide
these events into two categories: those in which material properties do not play a strong
part (the hydrodynamic regime, where density dominates) and those impacts in which
material properties do have a strong influence. The latter group of impact scenarios
normally occurs at ordnance velocities or less. For many reasons, this book focuses
predominantly upon this latter group, since these are not only of prime interest to
the material scientist but are also those events of greatest interest to the Australian
defence community in which small arms ammunition, high-velocity fragmentation
and knife attack dominate the thinking of those who set the Statements of Require-
ments (SoRs). Protection from blast, as well as high-velocity fragmentation, is not
only important but also very current, and has therefore been included within the threat
spectrum covered by this book.
As a corollary to this introductory section, I have personally carried out a number of
ballistic experiments in the “hydrodynamic regime” that have shown quite a dependence
upon material strength. So, even for armour systems designed to function against long-
rod penetrators and/or chemical energy weapons, understanding the dynamic properties
of the armour materials can still be very applicable. For further reading on kinetic energy
6 The Science of Armour Materials

(KE) threats (up to very long rods, etc.) the reader is referred to Hameed et al. (2004) and
Ogorkiewicz (2015).

1.2.1 Small arms ammunition

These range in calibre from the 5.56 and 7.62 mm rifle rounds, through the 9 mm hand-
gun bullets, up to 12.7 and 14.5 mm calibre, armour-piercing rounds. The latter two cal-
ibres are approaching the class of medium arms (>20 mm) and so have been excluded
from this short overview e however, details of their construction and the principles of
penetration, as well as the opportunities for defeat, are exactly the same across all cal-
ibres of KE projectiles. The armour technologist needs to understand what provides
these rounds with their penetrative power since this differs in all cases. The important
aspect is the core of the projectile, the internal penetrator, especially its nose shape
and material type, since this will govern possible defeat mechanisms e see Section
1.4. The following subsections therefore describe the constructional details of the
most common small arms ammunition, details which are also extremely valuable to
the numerical modeller e see Chapter 9.

1.2.1.1 Handgun bullets

As can be seen from Table 1.1, the nature, shape and geometry of the conventional,
lead-filled handgun rounds has not significantly changed in 150 years. In fact the
0.4400 Colt round from the 1860s is very similar to the current ‘44 Magnum’ bullet e
the lead-cores are much the same weight e the latter simply has a copper jacket. The
0.4400 SJHP round from Remington was originally designed as a dual-purpose cartridge
for use in both handguns and rifles. In armour testing, this bullet is one of two used for
certification of soft body armour and is typically chosen for evaluation of behind-armour
blunt trauma. It has been banned from private ownership in Australia and has been
excluded from the current version of the ballistic test standard, NIJ0101.06. On the

Table 1.1 Conventional handgun ammunition, past and present

0.4400 colt 0.5200 sharps 9 mm FMJ 0.4400 SJHP
Ammunition (US 1860s) (US 1860s) Remington Remington

Bullet and
deformed
core

Bullet 14.0 27.1 8.0 15.6

weight (g)
Core material Lead-based Lead-based Lead-based Lead-based
Introduction to armour materials 7

Table 1.2 Special handgun ammunition

Ammunition 7.62 3 25 mm Tokarev 5.7 3 28 mm SS195LF

Bullet and core

Bullet weight (g) 5.5 1.8

Core material Mild steel Aluminium

other hand, the 9-mm FMJ is probably the most widely used military and law enforce-
ment calibre in the world so it is with good reason that the 9-mm “Luger” is used to
evaluate the performance of body armour across many national test standards. The
lead filling in these conventional handgun rounds is easily deformed and can be arrested
by a layered pack of woven fabric, made from a high-performance fibre like Kevlar e
see Chapter 6.
Two nonconventional handgun rounds need to be mentioned here, as shown in
Table 1.2. The 7.62  25 mm (the first number is the calibre of the round in mm and
the second number is the length of the cartridge in mm) Tokarev is a steel-cored round
of unusual geometry. It is particularly effective against soft targets. The 5.7  28 mm
SS195LF is also of current interest. It was developed to replace the 9 mm Parabellum
but, unlike the 9 mm, is totally lead-free. The lightweight, aluminium core greatly re-
duces the risk of collateral damage but still requires special attention from the soft ar-
mour designer, compared with traditional lead-filled handgun rounds.

1.2.1.2 Rifle bullets

High-velocity, lead-filled rounds
Details of these high-velocity, lead-filled, rifle rounds are shown in Table 1.3. The first
two types are extremely common. Quite a few different countries manufacture the
7.62  51 mm NATO Ball L2A2 and users actually specify the required manufacturer.
For this reason, ballistic ranges usually stock a range of ammunition from different
manufacturers. The M80 NATO ball round was first adopted by NATO in 1954 but
is still commonly used for testing both body armour components and lightly protected
vehicles. Even though they are lead-filled, they are a heavy round, at w9.5 g, and pack
quite a punch when travelling at over 800 m/s. These two rounds are classically
described as “Level 3” threats.
The smaller-calibre variants, the 5.45  39 mm AK74 ball and the 5.56  45 mm
NATO M193 round, are lighter weight versions of the same. Lead-filled, but weighing
only w3.5 g, they were developed so that the combatant could carry more rounds.
8 The Science of Armour Materials

Table 1.3 Common lead-filled, ball ammunition

7.62 mm L2A2 7.62 mm M80 5.45 3 39 mm 5.56 3 45 mm
Ammunition NATO ball NATO ball AK74 ball M193

Bullet and
core

Bullet 9.3 9.5 3.5 3.6

weight (g)
Core material Lead-based Lead-based Lead-based Lead-based

High-velocity, cored rounds

This selection of high-velocity, cored rounds (see Table 1.4) is classically described as
belonging to the Level 3þ group of small arms ammunition. Of these, the
5.56  45 mm NATO SS109 round has become well established since 1979,
following a review by NATO of candidate rounds. It contains a small steel conoidal
core, near its tip, which is less likely to fragment in soft targets compared with the
lead-filled M193. Military users commonly specify it. Two variants of this round
need mention: the APHC variant which replaces the steel core with a tungsten carbide
one, giving the round more penetrative power; the M855A1 variant is relatively new
and is an interesting development e the core is manufactured from steel but it has been
designed to weigh the same as the tungsten carbide core of the APHC round. Varia-
tions such as this are actively pursued all of the time.
The 7.62 variants in this family of Level 3þ bullets contain a mild steel core.
Commonly known as the AK47, it is fired from the infamous Kalashnikov rifle still
very common in conflict zones around the world. The mild steel core was adopted
for its low cost and ease of manufacture. Whilst not intended as an armour-piercing bul-
let, the M43’s construction gives it armour-penetrating properties against both BASs
and lightweight military platforms. Its construction has been well documented e see
Fig. 1.4 e and well used in the R&D sector (Crouch et al., 2015a). The 7.62  54R
LPS is similar in nature but a much heavier round. Even though it is classed as a
ball round, because of its high lead content, the round is used in a number of test stan-
dards alongside conventional, armour-piercing rounds.

Armour-piercing rounds
Table 1.5 shows a selection of hard-cored, armour-piercing ammunition employed
across the various ballistic testing standards. The most common is the US 30-0600
Springfield M2 AP round, fondly referred to as the APM2. It has actually been out
 Introduction to armour materials
Table 1.4 Selection of cored, high-velocity ammunition
5.56 3 45 mm 5.56 3 45 mm 5.56 3 45 mm 7.62 3 39 mm 7.62 3 54R
Ammunition SS109 (M855) M855A1 enhanced APHC AK47 LPS

Bullet and core

Bullet weight (g) 4.0 4.0 4.6 7.9 10.0

Core material Steel cone Steel WC cone Mild steel Mild steel

9
10 The Science of Armour Materials

Figure 1.4 Cross-section of the 7.62  39 mm AK47 round showing the mild steel core,
lead-filling and copper-coated steel jacket.
After Crouch, I.G., Appleby-Thomas, G., Hazell, P., 2015a. A study of the penetration
behaviour of mild-steel-cored ammunition against boron carbide ceramic armours. International
Journal of Impact Engineering 80, 203e211.

of production for some time now, with supplies only available through military surplus
from WW2 and the Korean War. It remains the bullet of choice, however, for many
armour test standards and, of course, because it has been used for more than 50 years
there is an enormous stockpile of ballistic data e there is therefore great reluctance to
stop using it. Because it is not seen as a current battlefield round, it is also very popular
with researchers and armour technologists. It is still a very penetrating round with a
hardened steel, ogival-shaped core.
A similar round is the 7.62  54R API B-32, which has had the longest in-use mil-
itary service life of them all. It is, however, unpredictable, as a test round, due to some
irregularity on the quality of its steel core manufacturing. The actual core illustrated in
Table 1.5 shows slight asymmetry in the ogival portion of the core, for example.
The 7.62  51 mm P80 round is again similar to the APM2 but the shape of the
core is a lot more like the head of an arrow. This shape prevents this particular core
from being fragmented, as is often experienced with the cores of both the APM2
and the B32 rounds. The P80 is therefore considered to have a similar penetrative po-
wer, even though the core is significantly lighter. The shorter 7.62  39 mm API-BZ is
equally surprising in its ballistic performance.
Lastly, but by no means least, is the 7.62  51 mm, tungsten-carbide-cored, “FFV
round”, as supplied by NAMMO. FFV refers to the original supplier, Bofors AB, in
Sweden. Both it and its smaller sister, the 5.56  45 mm M995 round, were under
development during the late 1990s and, since 2000, have been available in niche quan-
tities. The core, with a sharp conical tip, is more penetrative than steel cores. Many
researchers have used it for the past two decades but its high price has limited its
availability.
 Introduction to armour materials
Table 1.5 Selection of cored, high-velocity ammunition
US 30-0600 7.62 mm 3 54 R 7.62 mm 3 51 7.62 mm 3 39 7.62 mm 3 51
Ammunition (AP M2) (B32) (P80) (API-BZ) (FFV)

Bullet and core

Bullet weight (g) 10.7 10.0 9.8 7.7 8.4

Core material Hardened steel Hardened steel Hardened steel Hardened steel Tungsten carbide

11
12 The Science of Armour Materials

Top view

Side view

Caliber
in. 0.10 0.125 0.15 0.22 0.30 0.45 0.50 0.622 0.712 0.787
mm (2.54) (3.18) (3.81) (5.59) (4.62) (11.43) (12.7) (15.8) (18.08) (20)

Wt. grain 1.35 2.65 5.85 17 44 147 207 400 600 830

Figure 1.5 Copy of original series of fragment-simulating projectiles.

Mascianica, F.S., 1980. Ballistic testing methodology. In: Laible, R. (Ed), Ballistic Materials and
Penetration Mechanics. Elsevier Scientific Publishing Co., Amsterdam.

1.2.2 High-velocity fragmentation

Protection from fragmenting munitions like high-explosive shells and, more
recently, IEDs is an extremely challenging task because such weapons eject multi-
ple steel fragments with a very broad, and varied, distribution of fragment sizes.
This was first recognised by scientists and engineers working at the Watertown
Arsenal Laboratories in the 1950s. Fig. 1.5 is a copy of the original set of chisel-
nosed projectiles forming an homologous series from 2.54 to 20 mm in diameter
(Mascianica, 1980). These fragment-simulating projectiles (FSPs), as schematically
shown in Fig. 1.6, are precision-manufactured from a medium-strength steel to a
military specification (Specification, 2006), and are heat-treated into a very specific
hardness range of 28e32 Rockwell C e this was chosen to represent the hardness
of typical munitions like the shell of the 105 mm HE round, a common overhead
threat since the 1960s.
Since that time, these FSPs have been universally adopted not only to test steel struc-
tures against overhead blast threats but also as a standard part of acceptance testing for
aluminium armours and armour steels, as well as combat helmets and soft body armour
components e see Chapter 11. When used, they do undergo plastic deformation but in a
controlled and reproducible fashion (see Fig. 1.7) and they have become totally accepted
by the global armour community as a design tool. With the aid of a saboted launching
system, they can be fired at velocities of up to 2000 m/s. Similar series of simulating
fragments are also available with different shapes, right circular cylinders, spheres
and cubes, but these are nowhere near as popular as the chisel-nosed FSPs for main-
stream armour work.

1.2.3 Stab and spike threats

The majority of stabbing incidents happen with the use of domestic knives (kitchen
knives, utility knives, sheath knives, lock knives, combat knives, penknives and other
Introduction to armour materials 13

Unless otherwise specified:

linear dimensions ±0.010”
angular dimensions ±0.5” 0.0348 ± 0.002
finish is 63 microinches
+0.000 0.034 ± 0.002
0.136
–0.010 0.005 Max.

+0.000 250
ø0.296 +0.000
–0.001 R0.340
–0.030
+0.000
ø0.273
–0.010

30º
30º
35º
ø0.309 ± 0.001
(0.354)
For reference only. Adjust the
length on the base surface to
meet indicated weight.
Figure 1.6 Extract from MIL-DTL-46593B (MR) showing precise geometry of the 0.300 FSP.
Specification, 2006. MIL-DTL-46593B (MR), Projectile, Calibers 22, 30, 50 and 20 mm
Fragment Simulating Projectiles.

Figure 1.7 Pairs of fragment-simulating projectiles (FSPs), untested and impacted, with
diameters of 5.6, 7.6, 12.5 and 20 mm. The impacted FSPs were tested against polymer
ceramic targets e see Section 7.7.
Naebe, M., Sandlin, J., Crouch, I.G., Fox, B., 2011. Novel lightweight polymer ceramic
composites for ballistic protection. Paper Presented at the ICCS 16, Porto, Portugal, 2011.

variations) (Hainsworth et al., 2008). Other weapons include scissors, bayonets,

samurai swords, screwdrivers and broken glass bottles (Nolan et al., 2012). Different
types of weapons which may be used for stab, puncture and slash attacks are shown in
Fig. 1.8, and recent reviews by Horsfall (2000), as well as Paul Fenne, from the Lon-
don Metropolitan Police (Fenne, 2009), and the DMTC (Crouch et al., 2014), show
that this threat is difficult to define and standardise.
As stated in the NIJ standard 0115.00, dated September 2000, ‘The threat posed by a
knife depends, amongst others things, on sharpness, pointedness, style, handle and blade
design, attacking angle, the physical condition of the attacker, and the skill of the attacker.’
14 The Science of Armour Materials

Figure 1.8 Typical array of knifes used in civilian crimes.

Fenne, P., 2009. Can the key design aims for body armour for police officers be achieved? Paper
Presented at the Next Generation Body Armour, London, UK.

All the stabbing weapons shown in Fig. 1.8 can be classified as either edged or
pointed. Hence, the act of stabbing can be described in terms of cutting or puncturing
of materials. Weapons such as knives, tools, swords and other implements designed to
perforate or cut materials have a long continuous cutting edge and are classified as
‘edged’ weapons. Stabbing describes the cutting action where an edged weapon travels
primarily in a direction normal to the surface of the material being penetrated, and a
slash describes the cutting action where the edged weapon travels parallel to the ma-
terial surface during an attack, using the knife-edge with a swinging motion. Prevent-
ing stab attacks is significantly more difficult than preventing slash attacks because,
during a stabbing event, the force is concentrated over a very small area at the tip of
the blade and the long cutting edge contributes a continuous source of damage. In
contrast, slashing by a knife-edge is easier to stop because the force of a blow is distrib-
uted along the cutting edge resulting in continuous damage to a larger area of the
target. Today, blade materials used for stab and slash attacks may include modern ma-
terials such as ceramics, synthetic sapphire, zirconium dioxide and even very hard
plastics. Other pointed weapons may have a slender rod with a pointed tip and these
include objects such as awls, ice axes, and ice picks, which can easily puncture mate-
rials. In fact, because of the small area of impact, they deliver a much larger kinetic
energy per unit area than handgun bullets.
Law enforcement centres around the globe have developed test methods that stan-
dardise both the attack weapon and how it is projected. Fig. 1.9 shows the range of
weapons used by the UK Home Office to assess the stab and spike resistance of armour
materials. Impacts are normally restricted to 33 or 50 J and the pass/fail criteria stipu-
lated in terms of residual perforation: the length of weapon extending into the ‘body’.
Another random document with
no related content on Scribd:
of the scientific world. Articles were written, pictures were made, and
for a time the new beasts were the theme of general discussion. The
first name given to the first specimen was the platypus, and duck-
billed platypus was the common designation for a time from 1799.
The colonists in Australia meanwhile named the duck-billed and
beaver-like animal a “water-mole,” from the fashion of its feet. The
name platypus, however, was dropped because it had already been
conferred on another creature. Then more learned heads were put
together, and a name was produced so long and hard in Latin, that I
dare not quote it. It meant, however, “bird-beaked-paradox.”[56]
Probably the reason the poor thing has survived such a name is that
it knows nothing about it.
The finding of these curious animals made it necessary to erect
another order in the mammalian class, an order that should embrace
creatures lower in the scale than the marsupials. Four species under
this order have been found, and probably there are no others. The
duck-bill and the echidna, or “thorny” creature, are the two most
interesting, and with most marked characteristics; to them we will
now devote our attention. We shall see that no name more apt than
that of “paradox,” could be given to creatures with such apparently
contradictory characteristics.

FOOTNOTES:
[55] Longfellow, “The Discoverer of The North Cape.”
[56] “Ornithorhynchus paradoxus.”
 LESSON XXVII.
THE MALLANGONG.

“I’m truly sorry man’s dominion

Has broken nature’s social union,
And justifies that ill opinion
Which makes thee startle.”

—Burns.
English settlers had not been long in Australia before they were told
by the natives of a very curious animal, the description of which
seemed rather that of an imaginary than of a possible creature. The
animal was called by the Australian natives a mallangong, and was
said to be very shy and secretive in its habits. The traders who heard
these stories concluded that they dealt with some fabulous beasts,
such as appear in the folk-lore of nearly all countries.
But one day a trader who was interested in natural science was
standing on the bank of a pond, when suddenly a new animal rose to
the surface of the water and swam noiselessly about. The creature
had the soft thick fur of a beaver or otter, now apparently black, as it
was wet and clung closely to the skin. Four legs the trader counted,
and as the feet came to the surface they showed that they were
webbed and pink-palmed like a mole’s feet. Stranger still, the small,
pointed head appeared to have neither eyes nor ears, yet bore
above the water a large, flat duck’s bill.
As the excited trader looked, the beast sank noiselessly out of sight.
He realized that he was the first white man who had seen a
mallangong, and that the strange tales were true tales. The
Australian wonder must be taken from the domain of folk-lore and
handed over to the investigations of science. But you must first catch
your mallangong.
He consulted the people who came to his trading-house, and they
told him that he must find a regular hunter of the mallangong; for the
beast was wary and scarce. At last an old native was brought to him,
who said that he knew how to get the desired prey; and at once a
hunting party was organized and armed under the old man’s
direction. What weapons did they take? Guns and knives? Not at all.
The old hunter had for his equipment a long, tough, slender stick,
pointed at one end. This was for prodding, not the mallangong, but
the ground. Two or three others of the party were given drills and
shovels, or pick-axes, and so prepared they set out, the old man
leading the way to the bank of a little stream.
As he slowly moved along he thrust his rod into the ground and
twisted it about. The others of the party considered this very dull
hunting.
“I have found him!” cried the old man. “Dig! dig! Behold the
mallangong!”
The shovels soon laid bare a little tunnel, which the guide said was
made by the animal and led to its nest. With some eagerness the
men followed up this tunnel, digging carefully. The process was long.
The tunnel wound about and seemed to have no end. At last, with a
cry of triumph, the guide laid open a small circular chamber, and
picked up a ball of fur. “Lo, the mallangong!”
The animal was rolled up, its long, flat bill being turned about so that
it rested on the fur-clad back. The feet were drawn up under the
body so as to be invisible, and the captive seemed either dead or
very sound asleep.
The trader carried his prize home, and soon it became lively and
friendly. Almost all creatures like sugar and milk; very few disdain
bread. The prisoner accepted kindly the novel food offered to it;
enjoyed the sunlight; lost all fear of humanity when it was not treated
with inhumanity; recognized the voice of its master; came at his call;
and when he seated himself in a chair promptly climbed to his
shoulder and surveyed its new surroundings with great interest.
Now that it was out of the water it was found to have nostrils in the
extremity of its bill, small, bead-like eyes shining from the mass of
fur, and ears acute enough, though they were merely holes hidden in
the depths of the fur. The hind-feet, while webbed like those of a
duck, were palmed like those of a mole, and spurred like those of a
rooster.
While it enjoyed the warmth of the sunshine, in which it would lie
curled up in a ball, as we sometimes see a cat or a dog, it preferred
darkness for its explorations. At night it crawled about the room,
worked its way up the wall by bracing against the furniture, and
rummaged everywhere with its busy feet and broad bill. Perhaps it
was searching for its friends, its native stream, and some soft earth
wherein to burrow.
A pile of shavings or raw cotton and straw afforded the nearest
approach to an earth bank that it could find in the warehouse, and in
such a heap it would dig until it reached the wall, and then it would
curl itself up and take some comfort in being securely hidden. A rat
or squirrel in such a case would have gnawed through the wooden
wall and departed without taking formal leave; but the mallangong
could not break prison in this fashion, because it has no true teeth,
only several horny protuberances on each jaw.
Examined at leisure, the marvellous animal was found to have cheek
pouches something like those of a squirrel, and evidently very
convenient as baskets for carrying food through the long tunnel
which led to its room. The temper of the creature seemed gentle; it
made no noise either for joy or pain, but a low whining sound, or, if
irritated, a soft growl. At first its owner thought it entirely defenceless,
but the old native showed him the spurs, and gave instances where
when angered the animal kicked out with its hind feet and inflicted a
long deep scratch, which was followed by symptoms of poisoning.
On examination it was found that the spur was traversed through all
its length by a tiny canal, which led to a gland or sac at the upper
part of the leg; the whole arrangement being very like the poison
gland and fang of a snake. This spur is present in a rudimentary
state in all young mallangongs; in the grown females it disappears,
and in the males it very greatly enlarges, no doubt because they are
expected to do the fighting for the entire family.
This animal, popularly called by foreigners a “duck-bill,” and by
scientific people a “bird-nosed-paradox,” is about twenty inches in
entire length; it has its bill covered with tough skin, and finished
where it joins the head with a fold or ruffle of skin; the fur is soft, fine,
thick, deep-brown above, and paler on the under part of the body.
The web in the hind-feet falls short of the strong toe nails, but on the
front feet it extends beyond the toes, so that when the feet strike
upon the water a broad surface is produced, enabling it to swim and
dive swiftly and silently. The duck-bill is entirely aquatic in its habits
and never lives far from water, making its tunnel with the round
chamber, in the bank of a pond or stream, so that it can come from
its front door and betake itself instantly to its favorite element. Its
manner of digging is like that of a mole. While digging it contracts or
folds back the superfluous skin or web of its fore-feet. The burrow
has two doors, one just above, the other below the water-line. The
tunnel is from twenty to fifty feet long, and the room at the end is
lined with dried grass and leaves, affording a soft bed for the young,
which are there reared until they are able to swim and forage for
themselves in the water.
The food of the duck-bill, or mallangong, is generally found in the
bottom of the stream or pond; the animal dives, turns over the stones
with its spade-like bill, and finds in the ooze worms, small crabs, the
larvæ of beetles, and water insects. Filling its cheek pouches with
this prey it ascends to the surface and swims quietly about, while it
carefully grinds its food into pulp with the bony, tooth-like projections
of the jaws. In this careful mastication the lowest of the mammals
sets some of the highest of the mammals a fine example.
The tail of the duck-bill is short, thick, and pointed; it is of very little
use in swimming, and for that matter the hind-feet are also little used
in the water, the broadly webbed fore-feet being the chief paddles.
For almost three quarters of a century the question of the young of
the duck-bill paradox was undecided. Report was that the creature
laid eggs; but then it was a mammal and fed its little ones with milk:
how could any mammal lay eggs? In 1884 the matter was finally
settled by indisputable proofs. The duck-bill mother lays two eggs,
less than an inch long and cased in strong but flexible shells. When
the little ones emerge from the shell they are exceedingly small, and
are fed with milk from milk-glands in the skin of the mother, to which
they attach themselves. They grow rapidly, and when they are
weaned are given insect-food. Shortly after this they are led out of
the tunnel, and at once swim with ease.
 LESSON XXVIII.
BESIDE AUSTRALIAN RIVERS.

“He can behold

Things manifold
That have not yet been wholly told—
Have not been wholly sung or said.”

—Longfellow.
The famous mallangong has a cousin almost as marvellous as itself.
Its common name is the porcupine ant-eater; its scientific name is
Echidna. When first the habits and anatomy of the duck-bill had been
investigated the question arose: Was this a lonely species, having
resemblances to many animals and close relationships with none;
sole representative of its order; as isolated as the hatteria? A search
among the animals of Australia brought to light another relative.
 “LOW DOWN IN THE SCALE.”
The new animal inhabited the rocky districts and was plentiful in New
South Wales. There, among the mountains, it burrowed in loose
sand brought down by the water-courses, or hid in crevices of the
rock. It wore the quill overcoat of the sea-urchin, and when coiled to
sleep looked not unlike a large specimen of that remarkable star-fish.
[57] In size the echidna is about like the European hedge-hog (not
our porcupine); it wears spurs like a rooster; it has the toothless jaws
and the long flexible tongue of the ant-eater. It is entirely
insectivorous in its diet, and from that and its quills, like a porcupine,
it has its common name, “the porcupine ant-eater.”
The head of the echidna is small and pointed, its eyes are nearly
hidden under its quills; so are its ears, which are merely holes
without external appendages. The frontal bone of the skull is
prolonged into a slim snout not unlike a slender bill. Near the end of
this snout are the nostrils. This snout is mostly covered with thin
skin. The mouth orifice is small, but large enough for all the
creature’s needs; its manner of eating is to thrust out a long, flexible,
delicate tongue covered with a glue-like substance. To this insects
adhere, and the tongue being drawn in, the insects are swallowed.
The echidna has no teeth; as its food is ants and small flies it needs
none. The tongue and palate are covered with fine spines which no
doubt crush the insect food.
On account of its diet this creature was formerly called the ant-eater,
but that name has been dropped, as it belongs to a very different
creature, the true ant-eater of the order Edentata.
The legs of the echidna are short and strong. The feet are not
webbed, but are furnished with very powerful claws, and are
admirably fitted for digging. The hind-feet have such a spur as was
described in the chapter on the duck-bill.
The body of the echidna is covered with a close short fur; among this
fur grow long spines thickly set, which project above the fur and
entirely hide it. These spines are directed from the head backwards,
but along the upper part of the body a large number of spines are
also turned inward; thus they cross each other, and form a thorny,
nearly impenetrable covering. The tail is very short, and is entirely
hidden by projecting spines. When the echidna rolls itself up the
spines stand out like a bristling thorn hedge all over the ball which it
forms, and this sharp armor is ample defence. The mouth of a dog,
or the hand of a man endeavoring to seize the curled up echidna
would be speedily withdrawn, pricked and bleeding.
The echidna seems quite aware of the defensive quality of its coat,
for when alarmed it tranquilly curls up and defies attack. Sometimes,
however, it prefers to take refuge in burrowing, and it will disappear
as quickly as a mole or a razor-shell clam.
The echidna is less easily tamed than the mallangong; it is restive,
and constantly tries to burrow out a path of escape. On the other
hand it seems of a hardier constitution; it has been carried across
the sea, and has lived for some years in foreign zoological gardens.
The mallangong has never survived an ocean voyage, and has been
seen in captivity only in its native country. When travelling at sea the
echidna is deprived of its natural insect-diet, but lives very
comfortably on sweet liquids.
The habits of the echidna are nocturnal. It generally sleeps most of
the day, and comes out at dark to prowl for insects. We might at first
consider this strange conduct, as the insects on which it feeds fly or
crawl about during the day and hide by night. But this is just what our
prickly hunter wishes. He is not content to pick up a toiling ant here,
and another there. When the ants are snugly housed after sundown
the echidna searches out their hills, tears open a hole in one side,
thrusts in his long nose, and then running out his slim, limber tongue
he twists it here and there, and the ants and their white larvæ[58]
bundles are collected by scores on its viscid surface.
Having gone from one ant-hill to another until its hunger is satisfied,
or the morning dawns, or it grows weary, the echidna retires to its
burrow or rock crevice. On the road it takes a drink of water, and
makes a dessert of a liberal quantity of sand and mud. As fowls need
some sharp bits of stone or shell in their gizzards to help grind up
their food, the echidna seems to need in its stomach gritty material to
grind the oily, insect bodies and keep them from packing. This need
of some coarse substance with food is not confined to fowls and the
echidna. Any sheep farmer will tell you that his sheep must be given
what he calls “roughness” with their food. The “roughness” is ground
or finely cut straw. If this is not given with corn and wheat, the sheep,
however well fed, will become thin and weak, because their food is
too rich to be well assimilated.[59] When sheep are grazed and not
fed, they gather their “roughness” for themselves, in dry leaves,
roots, stems, and little twigs.
In disposition the echidna is sluggish; seems to have no playfulness;
does not object to having its nose gently stroked, but makes no
friends, and except for its wonderful construction is not an interesting
creature.
In Tasmania there is the short-spined echidna, which has much
shorter and weaker spines and much thicker fur than the one just
described. In 1877 a new species living on a mountain thirty-five
hundred feet high was discovered in New Guinea. It also had fewer
spines and thicker, rougher fur. This mountaineer of the echidna
family is much larger than his relatives of lower regions.
No fossil remains of any great age have been found to prove that
these animals are of distant antiquity. We cannot tell in what age
they entered into existence. No remains of types connecting them
with lower vertebrates on the one hand, or higher mammals on the
other, have been discovered. The only fossil portion of an echidna
that has been thus far secured is a shoulder-bone, found in a bed of
bones belonging to extinct species of marsupial, or pouched
animals. This shoulder-bone indicated an animal larger than any
living echidna.
One echidna, called the tachyglossus of Van Dieman’s land, eats
grass and tender leaves as well as insects. It lives less among rocks,
as it is very fond of burrowing. This specimen of the echidna is a
marvellous digger. If disturbed it begins to make a great tearing of
earth with its five-toed feet, and sinks out of sight almost as if it went
down in water. Perhaps you have seen a crab perform this feat,
keeping its eyes fixed on you until, presto! it has vanished as if by
enchantment.[60]
The echidna, like its relatives, is a milk-giving, egg-laying animal.
Only one egg is laid at a time, and that is very small. The egg is
tucked into a fold of the mother’s skin, not a pouch such as the
marsupials have, but a long fold. Here it is kept warm until it hatches.
Until it has attained over one-third of its growth the mother nourishes
the young creature with milk.
The Echidnidæ have all very quick tongues, which dart in and out of
their tube-like mouths rapid as the play of a snake’s forked tongue.
Their mouths are very soft and delicate, and in burrowing the nose is
carefully shielded, while the claw-armed fore-feet do most of the
work. Owing to the quick movements of the tongue some naturalists
have abandoned the name echidna, which refers to the thorny coat,
and give the name tachy-glossus, “quick-tongued,” to the entire
family.

FOOTNOTES:
[57] See Nature Reader, No. 2, Lesson 40.
[58] Nature Reader, No. 2, Lesson 2.
[59] Cows fed entirely on grain and roots will gnaw at fence-posts
and palings in an effort to get the woody, coarse substance
supplied by coarse grass stems in their ordinary hay food.
[60] Nature Reader, No. 1, Lessons 1-5.
 LESSON XXIX.
A WALK AMONG WONDER TREES.

“The groves of Eden, vanished now so long,

Live in description and look green in song.
These, were my breast inspired with equal flame,
Like them in beauty, should be like in fame.”

—Pope.
We know that vegetable life has accompanied and probably
preceded all animal life. The long successions of animal existences
have been attended in their march through time by an equally long
succession of plants. All those ancient and wonderful living creatures
which we have noted have been and are now matched by equally
wonderful vegetable organisms.
A few of the wonderful plants of the world we now propose to set as
in a garden, and walk forth among them in fancy, and note their
marvels. Come then, let us take a walk among wonder trees.
Who is there that enjoys the strange, the unique, the rare, the grand
in nature? Let him come and walk slowly through this wonder grove
with us, and his passion for the strange and the unexpected may be
satisfied.
Our first wonder tree is notable only for its great age and vast size. It
is the Cowthorpe oak of Yorkshire, England. John Evelyn, the
pleasing writer and true gentleman of Charles Second’s time,
celebrates this oak in his book called “Sylva.”
This noble tree is fully fifteen hundred years old. Not the oldest tree
in the world then, for some of the olives in Gethsemane, near
Jerusalem, are supposed to be older than that by several hundred
years. The girth of the Cowthorpe oak at the
ground is seventy-eight feet. Forty persons can
stand inside its hollow hole. One of its main
branches broke off in a gale, and being cut up,
yielded five tons of timber. In Evelyn’s time the
branches shaded half an acre of ground. The
circumference of this tree is greater than that of
the Eddystone light-house. That famous light-
house was modelled after an oak tree, as
giving the best pattern of a well-rooted, firmly
resisting column.
This Cowthorpe oak is not the largest tree in
the world. There is a tree in South America
with a girth of one hundred and twelve feet,
and a California red-wood is known that
measures one hundred feet around just above
the ground. The red-woods belong to an
ancient order of vegetation, and doubtless it
could be said of the trees of the Carboniferous,
and next two or three world-building periods,
“There were giants in the earth in those days.” BEFORE
Australia is a land of wonders, animal and BLOSSOMS.
vegetable, and one of its curiosities stands
next in our grove—the bottle tree. The name is given because of the
shape of the tree, which resembles a gigantic bottle. This tree is sixty
feet high; the bark is brown, smooth, shining, like thick glass. The
girth of the tree is greatest just above the root, where it is forty feet in
circumference; it tapers very little until about forty feet above the
ground, where it narrows suddenly into a shape like the neck of a
bottle; and in this neck the branches have their base. The branches
are rather the long, pliant stems of compound leaves than real
branches; and the slender, numerous, small leaves give a light,
feathery effect to the foliage. This leafy crown forms the fantastic
cork, or stopper, of this quaint bottle. The leaf-stalks rise and then
bend over in a dome, or umbrella shape. The bottle trees grow in
groves of about thirty each, and stand a hundred feet apart, as
regularly as if planted by the hand of a gardener.
Be careful and do not tread on our next tree, the very pigmy of trees;
perfect in root, trunk, branches, leaves, flowers, fruit,—a dwarf
cherry tree from Japan. Are the trees of Japan then even more
diminutive than the little, olive-skinned, and almond-eyed people?
How did the skilful Japanese gardeners succeed in making this tiny
tree? For it is dwarfed not by nature, but by the art of man.
I once saw one of these dwarfed cherry trees. It was a foot high and
had a trunk about as thick as a lead pencil. The leaves were as small
as those of the clipped box plants which bordered the flower-beds in
my grandmother’s garden. There were perhaps twenty or thirty
small, red cherries upon it; but the cherries were large in proportion
to the tree. This is a curiosity merely, and artificial; we admit it for the
sake of contrast, and pass it by for a mighty tree that stands next,—
bo, the “god tree” from Ceylon.
The bo tree is famous for its long life and the reverence paid to it by
its Ceylonese worshippers. Perhaps it was the vigor and stately
beauty of the bo tree which suggested to the Ceylonese that it was
either divine, or the especial dwelling-place of a divinity. Alone the bo
tree stood, and for two thousand years had been the idol of tree-
worshippers. In 1887 a tremendous storm swept the island of Ceylon
and prostrated the ancient idol tree. The fragments were gathered by
the people and cremated with all the pomp awarded to dead kings.
The next specimen in our wonder grove comes from Africa, the
famous and beneficent rain tree. This is a tall and beautiful tree, with
widely spreading branches, gifted with the astonishing power of
extracting water out of apparently the driest soil and atmosphere.
While the earth seems absolutely parched, and the air is like the
breath of a furnace, the blessed rain tree draws from somewhere
abundant moisture, which it distills in a heavy shower from its leaves,
saturating all the earth beneath.
What could be more grateful to a hot and thirsty traveller than this
tree, bringing moisture from the very air of the burning desert?
Closely allied to the African rain tree is our next tree, brought to our
grove from Ferro, the smallest island of the Canary group. This
island is so dry that scarcely a rivulet or spring is found there, but on
its rocks grows a tree with narrow leaves that are green all the year.
A constant dewy cloud surrounds this tree, and is condensed,
dripping from the leaf points like the swift patter of a summer shower.
Under the branches the natives place cisterns and great jars, which
are kept always full by the copious supply provided by these trees.
[61]

Coming from the South Sea Islands, where there are so many
marvels, see next in our wonder grove the bread tree. The tree is of
moderate height, with large glossy leaves. The fruit is of about the
size of a Hubbard squash, and tastes like bread that has a little
sugar in it. It is eaten raw, and is also cooked in various ways. The
natives usually roast it in the ashes, as the negroes of the South
roast yams. The bread fruit forms the most important food staple of
the South Sea Islands, but is not so nourishing as the yam, wheat, or
corn; children fed entirely upon it lose flesh and strength. The bread
tree never finds an “off year” in bearing, nor a dull season; it is laden
with good fruit every year and all the year. From the timber the
natives can build their boats, and they make cloth from the bark. So
with a rain tree, a milk tree, and a bread-fruit tree one could do very
well for food, drink, shelter, and clothing.
As we have here in our wonder grove a bread tree, it is proper to put
a milk tree close by its side. Water, bread, milk, these three trees of
our collection afford all that is needful to support life. But the milk-
producer, the cow tree, is not a native of Africa; it grows in South
America, on the dry plains of Venezuela, where food and drink are
alike hard to obtain. Blessed then be the shadow of this admirable
tree, the hope of the perishing. The cow tree rises to a noble height.
Its straight smooth trunk lifts into the air seventy or eighty feet before
a branch springs from it. Then the wide arms extend in fair
proportions on every side, until the topmost twig is more than a
hundred feet from the ground. Tap the trunk anywhere, and an
abundant sap, having the appearance and taste of rich new milk or
cream, flows to revive the thirsty. The sap of our sugar maple runs
freely only in early spring, the sap of the cow tree is always ready.
What more appropriate than to place the butter tree beside the milk
tree? So we have placed it in our wonder grove, but nature planted it
elsewhere, for the butter tree grows in Africa. The butter of this tree
does not flow spontaneously. If people want butter it seems they
must take the trouble to make it, even if it comes from a tree. The
butter tree produces a fruit with a very rich kernel. When this kernel
is ground, the oil exudes and hardens into a fine quality of butter,
which will keep sweet for a year. David Livingstone, the celebrated
missionary traveller, made known to the world the virtues of the
butter tree.
Next let us have a tree that produces a fashion of confectionery. The
manna tree grows in Calabria and Sicily. In August the tree is
tapped, and the sap slowly exudes, hardening under the hot
southern sun to the consistency of fig paste. The flavor of the manna
while sweet is sickish to those unaccustomed to it. A taste for it
seems to come by habit. The product of the manna tree is by no
means so rich and useful as that of our beautiful sugar maple, but
the sap of the maple must be prepared for use by boiling.
Next to the confectionery tree let us place in our grove a medicine
tree. Who has not seen camphor, the clear white aromatic gum, so
useful in medicine and in the arts? This is the product of the
camphor tree of Japan. In Borneo, China, and the Malay Peninsula,
the camphor trees have the gum formed in the trunk in large lumps.
The camphor of other countries is obtained by boiling the wood of
the camphor trees, and then crystallizing the camphor so obtained.

FOOTNOTES:
[61] This tree, called by the natives the Til-tree, has almost
entirely disappeared.
 LESSON XXX.
STILL IN THE WONDER GROVE.

“Thus the seer

With vision clear
Sees forms appear and disappear;
In the perpetual round of strange
Mysterious change.”

—Longfellow.
The wonders of our grove are not yet exhausted. Indeed we might
spend a lifetime here, if we studied thoroughly its curiosities. We can
only look cursorily at a few more marvellous plants.
Here is a tree from Jamaica, called the life tree because it grows so
readily, and is so tenacious of existence. The life tree will grow in a
wet place or in a dry one; it cannot be killed by cutting down, for
every fibre of its roots seems to possess power to renew the tree.
Cut the leaves from the plant one by one, and where you drop them
on the ground they grow, sending forth a root from any one of the
severed ribs or veins. Cut the leaves into fragments and the
fragments will grow.
This power in leaves to send forth rootlets and start a new plant, is
not confined to the life tree. Gardeners will tell you that the plants of
the begonia tribe are grown by cutting off a portion of one of the
large handsome leaves which distinguish the begonias, and sticking
it in a little damp sandy soil. It soon roots and sends up vigorous
leaf-stems.
Beside the life tree behold its complement the death plant of Java,
called by the Javanese the kali-mujah. This is a beautiful plant,
growing nearly four feet high, with long, slender stems having upon
them thorns an inch in length. These stems are crowded with broad
leaves, thick, smooth as satin, heart-shaped, on one side a delicate
emerald green, and on the other a vivid crimson marked with cream-
color. From the midst of the leaf-stems rise the flower scapes, well
guarded about the blossom with fine, briar-like thorns. The blossoms
are milk-white, about the size and shape of a large cup. These
beautiful flowers pour out a strong perfume, which, though
agreeable, is overpowering and has poisonous qualities. If persons
inhale this fragrance for several minutes, they become faint, and
then unconscious; if shut up with the plant in a close room even a
strong man would soon die.
Insects that hover about the flower fall dead, and birds that come,
attracted by its red, white, and green splendors, wheel dizzily about it
and drop unconscious. Even at a distance of three feet the breath of
the kali-mujah will kill a bird or insect, and will give a man a severe
headache with convulsive twitching of the muscles of the face. Other
plants seem to avoid the kali-mujah, for none will grow in its vicinity.
But here is a more cheerful specimen. It should be the joy of all
boys,—the whistling tree from Nubia. Day and night, year in and year
out, this merry tree whistles tunes of its own composing—chorister of
trees! The leaves and stems are so constructed that this tree
becomes a shrill musical instrument, whistling loud and clear, even
when no wind seems to be stirring. We have all noticed the shiver
and murmur in a grove of pines, even in the hot stillness of a
summer noontide; the whistling tree like the pine never ceases its
peculiar music.
Our next wonder plant grows in water; it is a cousin of our white
pond-lily, it is the Victoria regia which grows in still pools in the
Amazon region. The leaves are round, and are from six to eight feet
in diameter. They are sharply turned up at the edge to form a rim, so
that each leaf is like a plate, the under surface is crimson, the upper
surface green with fine lines; on this elegant plate the flower lies.
Let us watch a blossom open. About half-past eight in the evening
the bud has slowly lifted itself above the pond, where it had grown
submerged. Once free from the water it shakes and quivers, as if
endowed with conscious life, and presently from the folded flower
one petal flies open; then for a little it rests; then is again agitated,
and a second petal expands. Then the agitation continues, the bud
flutters and trembles, and petal after petal spreads out; then a dozen
at a time are released from their close clasping, and at last behold
the great flower, two feet wide across its snow and gold centre, a
hundred snow-white petals composing the perfected bloom. From
the whole blossom exhales a delicate, rich, delicious perfume,
harmless as the breath of violets. The sun rises; the white petals
bend together, and, rocked on the parent pool, the Victoria regia
sleeps.
But as night draws on again the royal lily awakes. Now it is in its
perfection; the perfume is more subtle; the petals take a flush of the
palest pink; it rocks on the water and queens it through the night.
And so with a few waking and sleeping nights and days, the royal
lily’s life is done.[62] When the splendid blossoms and the vast green
leaves have perished the seed boxes or pods of the plant rise above
the water and ripen, and the Indians call them water maize, and eat
them.
Next to the lovely Regia let us place the century plant. The old notion
was that this “American aloe” bloomed only after one hundred years
of growth. Agave Americana is its true name, and when growing in a
cool climate it is very slow in attaining maturity. At any time between
ten and seventy years of age, it may send up a very tall flower stalk,
covered with large greenish yellow blossoms, which continue open
for several months. As soon as it has finished flowering it dies.
There are many members of the cactus and orchid families which
might appropriately be planted in our grove of wonders, to light it up
with their beauty, and amaze us with the marvels of their structure.
But for that matter not a plant that grows lacks mysteries and
marvels.
Of all strange, abnormal plants the carnivorous, or flesh-eating, are
the most singular. Several members of this family were described in
Nature Reader, No. 3. Those were all small and pretty plants, green