Msc Disertation for Emergent Technologies and Design programme at Architectural Association, 2008/09

1. Fibre Composite
Adaptive Systems
Maria Mingallon | Konstantinos Karatzas [MSc]
Sakthivel Ramaswamy [MArch]
Emergent Technologies + Design | Architectural Association | London | 2008/09

2. ARCHITECTURAL ASSOCIATION SCHOOL OF ARCHITECTURE
GRADUATE SCHOOL PROGRAMMES
COVERSHEET FOR COURSE SUBMISSION 2008/2009
PROGRAMME: Emergent Technologies and Design
TERM: Autumn 2009
STUDENT NAME(S): Konstantinos Karatzas, Maria Mingallon
SUBMISSION TITLE MSc Dissertation | Fibre Composite Adaptive Systems
COURSE TUTOR Mike Weinstock, Michael Hensel
SUBMISSION DATE: 12/10/2009
DECLARATION:
Signature of Student(s):
Date: 12/10/2009
“I certify that this piece of work is entirely my/our own and that any quotation or paraphrase from the published
or unpublished work of others is duly acknowledged.”

3. Contents
1 Biomimetics Research 9
Fibre Organisation Strategies in Nature
Thigmo-Morphogenesis
Adaptive Systems in Nature
Precedents
Smart Systems
2 Technology 27
Base Material
Sensing
Actuation
Energy
Control
3 Experiments 49
Preparation
Actuation
Actuation +Control
Sensing + Control
Sensing + Actuation + Control
4 Geometry 81
Local Geometry 83
Precedents
Topology
Actuation
Global Geometry 115
Precedents
Morphology
Material configuration
5 Environmental Performance 141
Global Morphology
Local Geometry
Information Processing
6 Conclusion + Further Research 149
Appendixes 155
A: Technology
B: Geometry
C: Manufacturing
Bibliography 241
Illustration Credits 244
Glossary 245

5. We would like to thank our tutors; Mike Weinstock for his involvement and invaluable
guidance, and Michael Hensel for his help and encouragement. George Jeronimidis, for
his immense help in developing our research and performing the physical experiments.
His research on biomimetics is the foundation for this project. We would also like to
thank Stylianos Dristas, for his essential input in evolving the geometry. Prof. Kevin
Kuang and W.J.Cantwell for sharing their knowledge and research on shape memory
alloys and fibre optics. Finally, we would like to thank Evan Greenberg, Tryfon Mantsos,
Trystrem Smith and all our Emtech colleagues for their support and feedback.
Acknowledgments

6. ‘Thigmo-morphogenesis’ refers to the changes in
shape, structure and material properties of biological
organisms that are produced in response to transient
changes in environmental conditions. This property
can be observed in the movement of sunflowers,
bone structure and sea urchins. These are all growth
movements or slow adaptations to changes in specific
conditions that occur due to the nature of the material:
fibre composite tissue. Nature has limited material;
remarkably all of them are fibres, cellulose in plants,
collagen in animals, chitin in insects and silk in spiders.
Natural organisms have advanced sensing devices
and actuation strategies which are coherent morpho-
mechanical systems with the ability to respond to
environmental stimulus.[1.0]
Architectural structures endeavour to be complex
organisations exhibiting highly performative
capabilities. They aspire to dynamically adapt to
efficient configurations by responding to multiple
factors such as the user, functional requirements and
the environmental conditions. Existing architectural
smart systems are aggregated actuating components
assembled and externally controlled, whose process
of change is essentially different from that of
Thigmo-morphogenesis. For example in a leaf, the
veins account for its form, structural strength and
nourishment, nevertheless they are an integral part of
the sensing and the actuation function. This process of
a coherent self-autonomous multi-functionality could
be termed as‘Integrated functionality’. Emulating such
a Morpho-mechanical system with sensors, actuators,
computational and control firmware embedded in a
fibre composite skin is the core of this research.
Performative abilities and intelligence of the fibre
composite adaptive system proposed, springs from
the integrated logics of its material behaviour, fibre
organisation, topology definition and the overall
morpho-mechanical strategy. The basic composite
consists of glass fibres and a polymer matrix. The
sensing function is carried out through embedded
fibre optics which can simultaneously sense multiple
parameters such as strain, temperature and humidity.
These parameters are sensed and processed as inputs
through artificial neural networks. The environmental
and user inputs, inform the topology to dynamically
adapt to one of the most efficient configurations of
the ‘multiple states of equilibrium’ it could render. The
topology is defined as a multi-layered tessellation
forming a continuous surface which could have
differentiated structural characteristics, porosity,
density, illumination, self-shading and so on. The
actuation is carried out through shape memory alloy
strips which could alter their shape by rearranging their
micro-molecular organisation between their ausentic
and martensitic states. The shape memory alloy strip
is bi-stable, but a strategic proliferation of these strips
through a rational geometry could render several
permutationandcombinationscreatingmultiplestates
of equilibrium, thus enabling continuous dynamic
adaptation of the structure.
Abstract

7. Aim
Hypothesis
Self-organisation is a process through which the internal organisation of the system adapts to
theenvironmenttopromoteaspecificfunctionwithoutbeingcontrolledfromoutside.Biological
systems have adapted and evolved over several billion years into efficient configurations which
are symbiotic with the environment.
To emulate this self-organisation process by developing a fibre composite material system that
could sense, actuate and hence efficiently adapt to changing environmental conditions is the
primary aim of this research.
Form, structure, geometry, material, and behaviour are factors which cannot be separated
from one another. For example, the veins in a leaf contribute to the overall form of the leaf, its
structure and geometry. At the micro scale the fibre material organisation compliments to the
responsive behaviour of the leaf. Therefore, the veins display an integral coherence within the
multiple functions they perform which could be termed as ‘Integrated Functionality’. Integrated
Functionality occurs in nature due to multiple levels of hierarchy in the material organization.
The premise of this research is to integrate sensing and actuation functions into a fibre
composite material system. Fibre composites which are anisotropic and heterogeneous offer
the possibility for local variations in their material properties. Embedded fibre optics would be
usedtosensemultipleparametersandShapememoryalloysintegratedintocompositematerial
for actuation. The definition of the geometry, both locally and globally would complement the
adaptive functions and hence the system would display ’Integrated Functionality’.
0.1 - Images from top, Showing the form of hibiscus leaves,
Structure at the bottom of lily pad,
Vein pattern of a leaf,
Microphoto of stomatawhich aid photosynthesis,

8. 8

9. This chapter is a comprehensive study of adaptive systems in
nature. Fibre organisation strategies in biological systems , which
allow for changes in shape and material properties with respect to
transient changes in the environment are investigated. The process
of Stimulus-Response co-ordination, in biological organisms range
from simple to complex configurations. Such configurations of
sensing devices, actuators and controllers are studied, both in
biology and man-made precedents.
1 Biomimetics Research
Thigmo-Morphogenesis Adaptive Systems Precedents Smart SystemsFibre Organisation

10. 10
Fibre Organisation Strategies in Nature
Biology makes use of remarkably few materials and
nearly all loads are carried by fibrous composites.
There are only four types of fibers: cellulose, collagen,
chitin and silks. These are the basic materials of
biology and they have much lower densities than most
engineering materials.They are successful not so much
of what they are but because the way in which they
are put together. The bulk of the mechanical loads in
biology are carried by these polymer fibres. The fibres
are bonded together by various substances such as
polysaccharrides, polyphenols and so on, sometimes in
combination with minerals such as calcium carbonate
(eg.mollusk shells) and hydroxyapatite (eg. bone). The
organisation of the fibres and the degree of interaction
between them provides the means of tailoring their
properties for specific requirements. For example, It
is the same collagen fibre that is used in low modulus
and highly extensible structures such as blood vessels,
intermediate modulus tissues such as tendons and
high modulus, rigid materials such as bone. [1.1]
The reason for all biological organisms being made
of polymers is probably that the synthesis of long
polymer chains based on carbon, oxygen, nitrogen and
hydrogen makes use of readily available chemicals and
can be controlled by enzymes at low temperatures.
The man-made counterparts of these biological
fibrous materials are high-performance fibres such as
nylon, aramid and highly-oriented polyethylene. The
use of fibres for making structural materials offers a
great deal of scope and flexibility in design. Fibres and
fibre-reinforced materials have an inherent property of
anisotropy of physical and mechanical properties and
heterogeneity. If properly exploited, they can provide
higher levels of optimisation than would be possible
with isotropic, homogeneous materials because
stiffness and strength can be matched to the loads
applied, not only in magnitude but also in direction.
In biology this is extremely common and happens as
a result of “growth under stress”. The magnitude and
direction of the loads that the organism experiences
as it develops provide the blueprint for the selective
deposition of new material, where it is needed and in
the direction in which it is needed. The best known
examples of this are the “adaptive” mechanical design
of bone and trees. In bone, material can be removed
from the under stressed parts and re-deposited in the
highly stressed ones ; in trees a special type of wood,
with different cellulose microfibril orientation and
cellular structure are produced in successive annual
rings when mechanical circumstances demand.
Growing a structure by producing and organising
fibres under the control of the loads that it has to carry
is extremely efficient.
Numerous patterns of load-bearing fibre architectures
are found in nature, each one of them being a specific
answer to a specific set of mechanical conditions and
requirements. In a sense there are no general design
solutions in biology but case specific ones, governed
nevertheless by common general principles. In
conventional engineering practices this process is
replaced by stress and structural analysis which is not
always accurate and often very complex. In recent
years, numerical techniques based on Finite Elements
have provided new tools to simulate the adaptive
design of nature and this approach has proved to be
very successful. [1.2]

11. 11
1.1 - Four basic types of fibres in nature, namely, collagen, cellulose, chitin and silks.
Collagen- The fibre material composition of the human femur shows the close packing of
fibres in parts which are highly stressed.
Cellulose-The section through the stem of a germanium reveals the closely packed bundles
of vessels and cells. The geometrical arrangement of closepacked integration produces a
complex structure, strong but flexible and capable of differential movement. The large
pale tubes in the centre are xylem vessels that transport water and nutrients up from the
root. The five bundles of pale green vessels are phloem cells, part of the vascular system
for the distribution of carbohydrates and hormones, and the smaller purple cells on the
perimeter are parenchyma cells, which are thin walled and flexible and can increase and
decrease in size by taking up or losing water. These changes cause deformations, which is
how the plant achieves movements such as bending towards light or turning around an
obstacle
Collagen Cellulose Chitin Silks

12. 12
Fibres are most efficient when they carry pure
tensile loads, either as structures in their own
right such as ropes, cables, tendons, silk threads
in spider’s webs or as reinforcement in composite
materials. Being slender columns, fibres cannot
carry loads in compression because of buckling,
even when partially supported laterally by the
matrix in composites. In the case of polymer
fibres, micro buckling at the micro-fibrillar
level within the fibre results also in very poor
compressive strengths. This problem is common
to both man-made and biological composites.
Since nature had no alternatives to fibres as
building blocks, it had to find ways of offsetting
the low efficiency of fibres in compression in
order to expand life beyond the limits of squidgy
invertebrate species or aquatic environments.
There are four solutions available in nature to
this problem: pre-stress the fibres in tension so
that they hardly ever experience compressive
loads; introduce high modulus mineral phases
intimately connected to the fibres to help carry
compression; heavily cross-link the fibre network
to increase lateral stability, and change the fibre
orientation so that compressive loads do not act
along the fibres.
Jim Gordon, says in ’The New Science of Strong
MaterialsandStructures’,whenoneisdealingwith
very heterogeneous fibre reinforced composite
systems, the distinction between materials and
structures becomes one of convenience rather
that of fact. This distinction becomes even more
elusive in biology because between the polymer
macromolecular chains at the nano metre level
and the functional organ at the millimetre or
metre levels there is a multiplicity of structures
which represent different levels of aggregation
of the load bearing materials. These hierarchical
organisations are the rule rather than the
exception in all biological composites. They
are probably the result of growth by successive
deposition of fibres and other materials.They are
difficult to analyse because of their complexity
but,byvaryingthedegreeofinteractionbetween
sub elements within a hierarchical level and
between levels, stiffness, strength, toughness,
etc. are modulated, tailored and optimised for
specific requirements. This kind of integrated
sub-structuring is a common theme in biology,
far more subtle and extensive than in any man-
made material or structure. [1.3]
Familiar biological materials such as tendons,
bones, muscles, skin and wood provide amazing
arrays of hierarchies spanning in typical
dimensions from 10-9 metres at the molecular
level, to typically 10-3 - 10-2 at tissue level and
100 and beyond at the organ level. In trees,
for example, the representative diameter of
the various sub structures covers a range from
101 metres at the diameter of trunk down to
10-8 metres diameter of cellulose protofibril;
i.e. ten orders of magnitude with perhaps eight
hierarchical levels: organ (trunk), tissue (wood),
wood cell, laminated cell walls, individual walls,
cellulose fibres, microfibrils and protofibrils.
Fibre material hierarchies
1.2 - The upper image shows collagen fibres of various sizes in a scanning electron microscope.
At bottom a much higher magnification image from a transmission EM shows
characteristic“banding”pattern of individual fibrils that make up the larger anatomic fibre.

13. 13
Thigmo-morphogenesis refers to the changes in shape,
structure and material properties that are produced
in response to transient changes in environmental
conditions. We are all familiar with the fact that many
plants are capable of movement, sometimes slow as
in the petals of flowers which open and close, tracking
of the sun by the sunflowers, the convolutions of
bindweed’s around supporting stems, snaking of roots
around obstacles, sometimes visible to the eye as in the
drooping of leaves when mimosa pudica is touched,
exceptionally very rapid, too fast to be seen as in the
closing of the leaves of the venus flytrap.
In all these examples, movement and force are
generated by a unique interaction of materials,
structures, energy sources and sensors. The materials
are the cellulose walls of perenchyma cells ,non-
lignified, flexible in bending but stiff in tension; the
structures are the cells themselves and their shape
with the biologically active membrane that can control
the passage of fluid in and out of the cells; the energy
source is the chemical potential difference between
the inside and the outside of the cells; the sensors
are as yet unknown. These systems are essentially
working as networks of interacting mini hydraulic
actuators, liquid filled bags which can become turgid
or flaccid and which, owing to their shape and mutual
interaction translate local deformations to global ones
and are also capable of generating very high stresses.
Similar mechanisms can be seen in operation when
leaves emerge from buds and deploy to catch sunlight.
How to package the maximum surface area of material
in the bud and to expand it rapidly and efficiently is the
result of very smart folding geometry, turgor pressure
and growth. [1.4]
Thigmo-morphogenesis
1.3 - Undisturbed delicate leaves of the sensitive plant, Mimosa pudica
when lightly touched, responds to stimulus.

14. 14
1.4 - Micrograph of stomata cells in a leaf, which open and close dur-
ing the process of photo-synthesis in response to sun light.

15. 15
Energy Input
(Stimulus)
Device
(Transduction)
Electrical
Signal
Filtering
Processing
Response
Behaviour
Adaptive mechanical design in
biology deals with the design
output arising from a set of inputs
on the evolving or growing organ
or organism. The inputs can
be external and internal loads,
environmental changes, etc.,
which are superimposed on the
genetic information available. The
evolutionary time-scale is a long one
and what we observe as a response
in biological organisms is the result
of all these inputs over long periods
of time. This complex process of
sensing and actuation could be
termed as ‘Morpho-Mechanical
Computation’. The energy input
or stimulus received from the
environment is transduced into
electric signals by biological sensing
devices. The electric signals are
further processed for an appropriate
responsive behavior.
Two other aspects of ‘Morpho
Mechanical Computation’ which
occur over much shorter time-
scales and which involve individuals
as opposed to whole species, are
Thigmo-morphogenesis, such
as various forms of tropism, the
opening and closing of stomata
cells in leafs and bone-remodelling.
What they show is the intrinsic
design flexibility due to fibres and
fibre architectures, hierarchies and
the modulation of interactions
between them, together with
growth, converging to the a specific
solution required for a specific
situation. In order to adapt to the
changes in circumstances, change
in fibre orientations, modifications
in structure and material properties
and the shapes in local and global
scales are altered. [1.5]
Morpho-Mechanical Computation
1.5 - Diagram showing the process of
Morpho-Mechanical Computation

16. 16
1.6 - Micrograph showing , Sensory filiform hairs of crickets for detection of
predators. Filiformhair length varies between 100 and 1500 μm

17. 17
One of the most interesting aspects of multi-
functionality and integration in biology is the
way in which receptors detect and amplify
mechanical strains and displacements.These
devices are called as mechanoreceptors.
They do exist in all creatures, plants and
animals as shown in the table 1.7.
The vibration amplifications in case of
insects, arthropods and crustaceans is
further elaborated. These species have
exoskeletons which, in their rigid state, are
stiff laminated composite structures made
of chitin fibres embedded in a highly cross-
linked matrix of proteins and phenolic
substances. The exoskeleton acts also as
the load, strain or displacement detector via
specialised organs, called sensilla, parts of
which are local modification of the laminated
structure of the exoskeleton to amplify the
strain information for the detector organ
connected to the nerve cell. These local
modifications are a combination of changes
in thickness, material stiffness and fibre
orientation function as strain concentrations
and mechanical signal amplifiers. These are
equivalent to drilling holes into structural
components and embedding strain gauges
in the regions near the holes to get an
amplification of the remote state of strain of
the structure.
The comparison between the vibration
graphs shows the efficiency of
mechanoreceptors in crickets which have a
highly precise vibration sensing as against
man-made sensing devices which pick up
vibrations. [1.8]
Chemical (most animals and some plants)
Vibration (hair sensors in insects, spiders, scorpions, hearing)
Infrared (beetles, snakes)
Fluid-flow (various insects, spiders, crustaceans, fish, amphibians)
Strain (insects, arthropods)
Pressure (fish)
Touch (most animals and some plants)
Electrical (fish)
Magnetic (fish, birds)
Radiation(most animals –photoreceptors / vision)
Mechano-Receptors
Biological Sensing Devices
1.8 - Comparison between an Input (tapped metal plate) sensor
and cricket hair response (frequency range 200-500 Hz)
1.7- Table showing Mechano- Receptors of several organisms

18. 18
Adaptive systems in nature have an incredible
Stimulus-Response coordination. The simplest
type of response is a direct one-to-one stimulus-
response reaction. A change in the environment is
the stimulus; the reaction of the organism to it is
the response.
Natural adaptive systems range from simple
to complex configurations of sensing devices,
actuators, controller logics and inherent energy
generators. The adaptive potential is a resultant
of continuous evolutionary processes to the
environmental pressures under gone by the
organism. Lower level organisms such as amoeba,
fungi and plants display a simpler process of
stimulus response co-ordination as against higher
level organisms such as animals which respond to
multiple stimuli.
Lower-level Organisms
In case of lower level organisms such as non-
lignified plants adaptive behavior is entirely
dependent on control of turgor pressure inside
the cells to achieve structural rigidity, pre-stressing
the cellulose fibres in the cell walls at the expense
of compression in the fluid. Trees pre-stress
their trunks with the outermost layers of cells
being prestressed in tension to offset the poor
compressive properties of wood. [1.7]
In single-celled organisms, adaptive behavior
is the result of a property of the cell fluid called
irritability. In simple organisms, such as algae,
protozoan’s, and fungi, a response in which the
organism moves toward or away from the stimulus
is called taxis.
Therefore the sensing and actuation functions are
integrated within the definition of the material
properties itself. The adaptive behavior emerges
throughthestrategicdefinitionofthefibrematerial
hierarchies in multiple scales.
The energy required for actuation is also generated
within the material system, In case of plants,
through the process of photosynthesis and
distribution of nourishment to alter the osmotic
pressure and chemical disintegration in case of
single celled organisms.
Adaptive systems in nature
s a
e
Sensing
Actuation
Energy
1.9 - Microgaph showing Parenchyma cells in plants which act as mini hydraulic
actuators, by changing the osmotic pressure inside their cell walls.

19. 19
s a
e
c
Sensing
Actuation
Control
Energy
In higher level organisms, adaptive behavior
involves the synchronization and integration of
events in different parts of the body, a control
mechanism, or controller, is located between
the stimulus and the response. In multi-cellular
organisms, this controller consists of two basic
mechanisms by which integration is achieved,
chemical regulation and nervous regulation.
In chemical regulation, substances called
hormones are produced by well-defined groups of
cells and are either diffused or carried by the blood
to other areas of the body where they act on target
cells and influence metabolism or induce synthesis
of other substances. The changes resulting from
hormonal action are expressed in the organism
as influences on, or alterations in, form, growth,
reproduction, and behaviour.
In animals, in addition to chemical regulation via
the endocrine system, there is another integrative
system called the nervous system. A nervous
system can be defined as an organized group of
cells, called neurons, specialized for the conduction
of an impulse, an excited state from a sensory
receptor through a nerve network to an actuator,
the site where response occurs.[1.8]
Organisms that possess a nervous system are
capable of much more complex behaviour. The
nervous system, specialized for the conduction of
impulses, allows rapid responses to environmental
stimuli. Many responses mediated by the nervous
system are directed toward preserving the status
quo,orhomeostasis,oftheanimal.Stimulithattend
to displace or disrupt some part of the organism
call forth a response that results in reduction of
the adverse effects and a return to a more normal
condition. Organisms with a nervous system are
also capable of a second group of functions that
initiateavarietyofbehaviourpatterns.Animalsmay
go through periods of exploratory or appetitive
behaviour, nest building, and migration. Although
these activities are beneficial to the survival of
the species, they are not always performed by
the individual in response to an individual need
or stimulus. Finally, learned behaviour can be
superimposed on both the homeostatic and
initiating functions of the nervous system.[1.9]
Therefore, higher level organisms have far more
sophisticated and complex system for sensing
and actuation functions. There is a multifarious
integration between sensors, controllers and
actuators. To maintain homeostasis of the
organism, the stimulus generated by multiple
sensor inputs, go through filter processing which
leads to decision making capabilities in higher level
organisms. An equivalent to this in the man-made
world would be artificial neural networks which
have multiple inputs fed into processors which
generated multiple outputs based on predefined
rules.
The energy required for actuation is again
generated within the organism by the process of
metabolism.
Higher-level Organisms
1.10 - Neurons, forming neural networks in the nervous system
and a neuron cell group responsive to multiple stimuli.

20. 20
Architectural structures or building envelopes could be
viewed as systems which need to self-regulate, adapt to the
environmental changes and respond to natural elements such
as sun, wind, rain etc. to achieve a comfortable micro climate.
Environmentally responsive buildings, also called as intelligent
buildings employing IBMS (Intelligent Building Management
Systems) function as a collection of devices such as louvers and
shades, controlled by a central computer that receives data from
remote sensors and sends back instructions for activation of
these mechanical systems.
On the contrary, natural systems are quite different wherein
most of the sensing, decision making and reactions are entirely
local and the global behavior is the product of these local
actions. This is true across all scales, from small plants to large
mammals. When we run for a bus, we do not have to make any
conscious decisions to accelerate our heartbeat, increase our
breathing rate and volume or open our pores to regulate the
higher internal temperature generated. This concept of local
decision making and reacting to external conditions is termed
as cybernetics.[1.11]
Noebert Wiener introduced the term ‘Cybernetics’ in 1949.
The concept of cybernetics includes information theory and
practice, from transmission to reception, as well as subsequent
manipulation and utilization of the information to control
regulatory processes of living organisms, societies, buildings
and engineering situations. Information plays a decisive role
in the operation of both living organisms and buildings. The
emissions and transmissions which constantly emanate from
infinitely many sources such as the environment are converted
into information by the agents which can use them as a basis
for action or inaction. Information can reach the receiver without
being passed along and manipulated within; so that the system
governsitselfbyadjustingaccordingly.However,informationcan
also have its origin within the living organism or buildings (such
as functional and spatial requirements). This feedback within a
system is a special form of information in living processes which
allows growth, adaptation or rather self-regulation.
Living organisms perceive information through their senses.
The senses serve the organism by obtaining information about
the environment, like needs for survival, namely food, safety
and reproduction. The acquisition of information is partly
conscious. Living organisms react to many external as well as
internal signals without involving consciousness, by assimilating
them unconsciously or subconsciously like the tanning of skin
by deposition of melanin when exposed to sunlight does not
involve the brain.[1.12]
It is this flexibility, reactive and transformational capacities of
biological organisms that scientists are now seeking to replicate
in materials, computers, robotics and buildings. In biomimetics,
scientists look at everything from the way the brain learns
through trial and error, (so that robots may do the same), to the
way a fish moves through water (so the submarines can become
similarly more flexible and efficient by reducing central control).
This level of biomimicry takes into understanding the aspect of
self-organization in biological organisms.[1.13]
There are some precedents which have endeavoured to achieve
the self -organisational process observed in nature. We shall
briefly discuss the system configuration of sensors, actuators,
control and energy deployed in these precedents in relation to
the higher and lower level organisms discussed in the previous
section of adaptive systems in nature.
Precedents
“The ultimate smart structure would design itself. Imagine a bridge
which accretes materials as vehicles move over it and it is blown
by the wind. It detects the areas where it is overstretched and adds
material until the deformation falls back within a prescribed limit…
The paradigm is our own skeleton where material deposition happens
in parts which require greater strength.”[1.10]
- Adriaan Beukers and Van Hinte

21. 21
‘Hyposurface’ was developed by Mark
Goulthorpe of Decoi architects as an
interactive installation in Birmingham
Hippodrome in 1999. The responsive
wall measures approximately 8
metres wide and 7 meters high. The
project was collaboration between
architects, mathematicians, computer
programmers and multimedia experts.
The hyposurface transforms from being
a flat plane into a curved plane by
moving the components up and down
by up to 60cm. The surface, extremely
varied in its motions and highly
dynamic, reacts to environmental
influences. The stimuli are picked up
by sensors responsive to video, sound,
light, heat, movement and so on. The
actuation was carried out through
arrays of pneumatic pistons, which are
activated in real time to the stimuli.
The control system processing the
information from sensors calculates
and signals to each piston a precise
instruction at real-time speed. The
wall responds in sympathy with a clap
from an observer and does not simply
respond as a delayed reaction.
The sensors, actuators and the control
technology were developed to react
within milliseconds to pulses racing
from one side to another at speeds
of 50 kilometres an hour. The surface
was fractioned into small plates
interconnected by rubber squids. The
geometry of the curved plane (during
actuation) is defined by triangular
plates to enable double curvatures.
[1.14]
The responsive behaviour of the
hyposurface is different from the
self-organisation process of adaptive
systems in nature. The system consists
of sensors and actuators, but the
information processing or control and
the energy required for the actuation
of the pneumatic pistons are sourced
externally.
s a
ec
Hypo-Surface
1.11 -Active responsive wall ‘Hypo-surface’ developed by Mark
Goulthorpe with motion sensors and pneumatic actuators.
1.12 -Diagram showing the configuration of sensors and actuators form-
ing a responsive system with external control and energy input.

22. 22
s a
e
Cartesian wax is a material system
developed by Neri Oxman for the
exhibition‘Design and the Elastic Mind’
at the MoMA - Museum of Modern
Art in 2008. The project explores
the notion of material organization
as it is informed by structural and
environmental performance. It is a
prototype for an environmentally
responsive skin and an exploration into
building envelope design. The material
system defined, integrates structural
and environmental elements of the
building skin. The structural elements
provide for an optimized distribution
of load, while the environmental
elements allow for the infiltration of
light and heat to and from within the
skin. Integrated solutions may prove
to be more sustainable as they are in
the natural and biological world. Less
redundant and more custom-fit to their
environment, space and structure can
now be shaped and manufactured
using state-of-the-art fabrication
techniques and technologies. It is a
well known fact that in nature, shape
is cheaper than material. In man-
made design, this was never the case.
Material is traditionally assigned to a
shape by way of post-rationalizing its
geometry. By using softwares to create
new composite materials Oxman has
been able to replicate the processes of
nature, creating materials that are able
to adapt to light, load, skin pressure,
curvature and other ecological
elements.[1.15]
The topology is defined as a continuous
tiling system, differentiated across its
entire surface area to accommodate for
a range of conditions accommodating
for light transmission, heat flux, and
structural support. The surface is
thickened locally where it is structurally
required to support itself, and
modulates its transparency according
to the light conditions of its hosting
environment.Twelvetilesareassembled
as a continuum comprised of multiple
resin types, rigid and flexible. Each tile
is designed as a structural composite
representing the local performance
criteria as manifested in the mixtures of
resin. [1.16]
In this case the material system
is predefined with sensing and
actuation functions. The changes in
the environmental heat flux are used
to change the state of the resin from
flexible to rigid and hence manipulate
the transparency of the surface. The
adaptive mechanism here is similar
to that of lower level organisms,
where the sensing, actuation and the
energy required for the actuation is
generated within the system. There is
no information processing or decision
making involved and the material
seamlessly responds to the changes in
the environmental conditions.
load, while
Cartesian Wax
1.13 -Resposive material system‘Cartesian Wax’
developed by Neri Oxman.
1.14 -Diagram showing the configuration of sensors, actuators and
energy forming an integral part of the material system.

23. 23
s a
e
c
NASA is currently working with Boeing
and the U.S. Air Force on the Active
Aero-elastic Wing (AAW) F/A-18 project
in a quest for developing a morphing
aircraft that changes its shape in flight.
TheAircraftofthefuturewillnotbebuilt
of traditional, multiple, mechanically
connected parts and systems. Instead,
aircraft wing construction will employ
fully integrated, embedded “smart”
materials and actuators that will enable
aircraft wings with unprecedented
levels of aerodynamic efficiencies
and aircraft control. The availability of
strong, flexible composite structures
and miniaturized computers and
motors point the way toward seamless
wings that will one day bend to achieve
flight control as effortlessly as a bird
does. [1.17]
The smart plane would respond to the
constantly varying conditions of flight,
sensorswillactlikethe“nerves”inabird’s
wing and will measure the pressure
over the entire surface of the wing. The
response to these measurements will
direct actuators, which will function
like the bird’s wing “muscles.” Just as a
bird instinctively uses different feathers
on its wings to control its flight, the
actuators will change the shape of the
aircraft’s wings to continually optimize
flying conditions. Active flow control
effectors will help mitigate adverse
aircraft motions when turbulent air
conditions are encountered.
Intelligent systems composed of these
sensors, actuators, microprocessors,
and adaptive controls will provide an
effective “central nervous system” for
stimulating the structure to affect an
adaptive“physicalresponse.”Thecentral
nervous system will provide many
advantages over current technologies.
The proposed AAW Vehicles will be
able to monitor their own performance,
environment, and even their operators
in order to improve safety and fuel
efficiency, and minimize airframe noise.
They will also have systems that will
allow for safe takeoffs and landings.
Researchers at NASA Langley Research
Center are taking the lead to explore
these advanced vehicle concepts and
revolutionary new technologies. [1.18]
The process of morpho mechanical
computation in the smart plane is
similar to that of higher level organisms.
There are multiple inputs from the
environment such as temperature,
drag coefficient, turbulence and so on;
these multiple sensor inputs would be
processed by controllers similar to that
of the central nervous system. Then the
actuation would be carried out through
the actuators strategically positioned
long the surface of the wing span.
load, while
Smart Plane
1.15- Morphing smart plane , developed by NASA Dryden Flight Research
Centre shows advanced concepts for the aircraft of the future
1.16 -Diagram showing the configuration of sensors , actuators, controllers and
energy forming and integrated and cohesive smart adaptive system.

24. 24
Smart systems
All around us are living things that sense and react to the
environment in sophisticated ways. As structures have become
more complex and are being asked to perform ever more
difficult missions, there has been an ever increasing need to
build“intelligence”into them so that they can sense and react to
their environment. Examples include buildings that can sense,
react and survive earthquakes and spacecraft that can sense
and repair damage autonomously. To perform these functions
successfully a “nervous system” is required that performs in
a manner analogous to those of living things sensing the
environment, conveying the information to a central processing
unit (the brain) and reacting appropriately. Fiber optic
technology has enabled the nerves of the system to be realized.
Using hair-thin glass fibers as information carriers and sensors
that may be built directly into the fibers with no increase in the
overall size, it is possible to create long strands of fibre sensors
capable of measuring strain, pressure, temperature, and other
key parameters. These sensor “strings” may then be embedded
into the structural materials with no degradation in overall
strength, resulting in “smart structures” with built in nervous
systems. Such structures could achieve active control, where a
structure senses environmentally induced structural changes
and reacts in real time.[1.19]
The term smart materials and structures are used to describe this
unique collaboration of material and their structural properties
with fibre optic sensors and actuation control technology. Smart
structures constructed from materials with fibre optic nerves
could continuously monitor the loads imposed on them as
well as their vibration state and deformation. In addition, strain
sensing may be capable of assessing damage and warning of
impending weakness in structural integrity or improving quality
control of thermo set composite materials during fabrication
through cure monitoring. This could lead to greater reliance
in the use of advanced composite materials and the usage of
optimum material based on specific loading conditions.
A large scale research effort is currently underway to use
advanced composite materials extensively in bridges. This
research is addressing issues of corrosion, rehabilitation, and
monitoring and involves new concepts and designs in bridge
repair and construction. One of the most significant advances is
the replacement of steel pre-stressed tendons with ones made of
advanced composite materials. These fiber reinforced polymers
are practically immune to corrosion and also lead themselves to
internal monitoring by means of embedded fiber optic sensors.
A structurally integrated sensing system could monitor the state
of the structure, throughout its working life. It could determine
the strain, deformation, load distribution and temperature or
environmental degradation experienced by the structure. The
first smart bridge to be built with structurally integrated fiber
optic strain and temperature sensors was opened in 1993 in
Calgary.
In more advanced smart structures the information provided by
the built-in sensor system could be used for controlling some
aspect of the structure, such as its stiffness, shape, position or
orientation. These systems could be called adaptive (or reactive)
smart structures to distinguish them from the simpler passive
smart structures. A more appropriate term for structures that
only sense their state might be “Sensory Structures”. Smart
structures might eventually be developed that will be capable
of adaptive learning and these could be termed “Intelligent
Structures”. Indeed, if we consider the confluence of the four
fields- structures, sensor systems, actuator control systems,
and neural network systems- we can appreciate that there is
the potential for a broad class of structures such as, Controlled
Structures, Self-learning Reactive Structures, Smart Structures
and Self-learning Smart Structures. Therefore smart structures
open up a new panorama for biomimetic systems.
As Eric Udd says, “This era would see the marriage of fibre optic
technology and artificial intelligence with material science and
structural engineering. Major structures constructed in this period would be
constructed with built-in optical neuro-systems and active actuation control
that would make them more like living entities than the inanimate edifices we
are familiar with today. To carry this biological paradigm one step further, it may
even be possible to contemplate future structures that have the capacity for
limited self-repair. Indeed, if we think of the new frontiers for engineering as
being in space or underwater, self-diagnosis, self-control, and self- healing may
not be so much esoteric as vital”. [1.20]
1.17 -Calgary bridge built with embedded fibre optic sensors.

25. 25
Actuator
Systems
Controlled
Structures
Smart
Structures
Smart
Adaptive
Structures
Intelligent
Adaptive
Structures
Self-
learning
Reactive
Structures
Self-
learning
Smart
Structures
Structures
Neural Network Systems
Sensor
Systems
1.18 -Diagram showing Smart Systems possible by the confluence of four disciplines: materials and struc-
tures, sensing systems, actuator control systems, and adaptive learning neural networks.

27. This chapter will explore all the different technologies used for our
research and development of the project. For building our physi-
cal models and achieving the desired functionality of the system
-both in theory and in practice-, many possibilities were open and
specific choices had to be made. Here we explain our choices and
give a thorough background of the technology behind our material
system.
2 Technology
Sensing Actuation Energy ControlBase Material

28. 28
Fibre Composites
Base Material
Man made composites are not new. The first composite materials
were developed many years ago:
• Mud bricks reinforced with straw (antiquity)
• Glass Reinforced Plastic - GRP (1940s)
• Carbon Fibre Reinforced Plastic – CFRP (1960s)
In its most basic form a composite material is one which is composed
of at least two elements working together to produce material
properties that are different to the properties of those elements on
theirown[2.1].Inpractice,mostcompositesconsistofabulkmaterial
(the ‘matrix’), and a reinforcement of some kind, added primarily to
increase the strength and stiffness of the matrix [2.2,2.3,2.4]. This
reinforcement is usually in fibre form.
Today, the most common man-made composites can be divided into
three main groups:
Polymer Matrix Composites (PMC’s):These are the most common and
have been selected for the construction of this project. Also known
as FRP - Fibre Reinforced Polymers (or Plastics) - these materials use
a polymer-based resin as the matrix, and a variety of fibres such as
glass, carbon and aramid as the reinforcement.
Metal Matrix Composites (MMC’s) - Increasingly found in the
automotive industry, these materials use a metal such as aluminium
as the matrix, and reinforce it with fibres such as silicon carbide.
Ceramic Matrix Composites (CMC’s) - Used in very high temperature
environments, these materials use a ceramic as the matrix and
reinforce it with short fibres, or whiskers such as those made from
silicon carbide and boron nitride.
PMC | Resins
The primary functions of the resin are to transfer stress between
the reinforcing fibers, act as a glue to hold the fibers together, and
protect the fibers from mechanical and environmental damage.
Resins are divided into two major groups known as thermoset and
thermoplastic.
Thermoplastic resins become soft when heated, and may be shaped
or molded while in a heated semi-fluid state and become rigid when
cooled. Thermoset resins, on the other hand, are usually liquids or
low melting point solids in their initial form. When used to produce
finished goods, these thermosetting resins are “cured” by the use
of a catalyst, heat or a combination of the two. Once cured, solid
thermoset resins cannot be converted back to their original liquid
form. Unlike thermoplastic resins, cured thermosets will not melt
and flow but will soften when heated (and lose hardness) and once
formed they cannot be reshaped. Heat DistortionTemperature (HDT)
and the Glass Transition Temperature (Tg) is used to measure the
softening of a cured resin. Both test methods (HDT and Tg) measure
the approximate temperature where the cured resin will soften
significantly to yield (bend or sag) under load.
The most common thermosetting resins used in the composites
industry are unsaturated polyesters, epoxies, vinyl esters and
phenolics. There are differences between these groups that must be
understood to choose the proper material for a specific application.
Polyester
Unsaturated polyester resins (UPR) are the workhorse of the
composites industry and represent approximately 75% of the total
resins used.Thermoset polyesters are produced by the condensation
polymerization of dicarboxylic acids and difunctional alcohols
(glycols). In addition, unsaturated polyesters contain an unsaturated
material, such as maleic anhydride or fumaric acid, as part of the
dicarboxylic acid component. The finished polymer is dissolved in
a reactive monomer such as styrene to give a low viscosity liquid.
When this resin is cured, the monomer reacts with the unsaturated
sites on the polymer converting it to a solid thermoset structure [2.5].
A range of raw materials and processing techniques are available
to achieve the desired properties in the formulated or processed
polyester resin. Polyesters are versatile because of their capacity to
2.1 Classification of composite materials
2.2 Diagram showing the evolution of
engineering materials
2.3 Examples of composite materials uses

29. 29
be modified or tailored during the building of the polymer chains.They
have been found to have almost unlimited usefulness in all segments
of the composites industry. The principal advantage of these resins is
a balance of properties (including mechanical, chemical, electrical)
dimensional stability, cost and ease of handling or processing.
Unsaturated polyesters are divided into classes depending upon the
structures of their basic building blocks. Some common examples
wouldbeorthophthalic(“ortho”),isophthalic(“iso”),dicyclopentadiene
(“DCPD”) and bisphenol A fumarate resins. In addition, polyester
resins are classified according to end use application as either general
purpose (GP) or specialty polyesters. [2.5]
Epoxy
Epoxy resins have a well-established record in a wide range of
composite parts, structures and concrete repair. The structure of the
resin can be engineered to yield a number of different products with
varying levels of performance. A major benefit of epoxy resins over
unsaturated polyester resins is their lower shrinkage. Epoxy resins
can also be formulated with different materials or blended with other
epoxy resins to achieve specific performance features. Cure rates can
be controlled to match process requirements through the proper
selection of hardeners and/or catalyst systems. Generally, epoxies are
cured by addition of an anhydride or an amine hardener as a 2-part
system. Different hardeners, as well as quantity of a hardener produce
a different cure profile and give different properties to the finished
composite.
Epoxiesareusedprimarilyforfabricatinghighperformancecomposites
with superior mechanical properties, resistance to corrosive liquids
and environments, superior electrical properties, good performance at
elevatedtemperatures,goodadhesiontoasubstrate,oracombination
of these benefits. Epoxy resins do not however, have particularly good
UV resistance. Since the viscosity of epoxy is much higher than most
polyester resin, requires a post-cure (elevated heat) to obtain ultimate
mechanical properties making epoxies more difficult to use. However,
epoxies emit little odor as compared to polyesters.
Epoxy resins are used with a number of fibrous reinforcing materials,
including glass, carbon and aramid. This latter group is of small in
volume, comparatively high cost and is usually used to meet high
strength and/or high stiffness requirements. Epoxies are compatible
with most composite manufacturing processes, particularly vacuum-
bag molding, autoclave molding, pressure-bag molding, compression
molding, filament winding and hand lay-up.
Vinyl Ester
Vinylestersweredevelopedtocombinetheadvantagesofepoxyresins
with the better handling/faster cure, which are typical for unsaturated
polyester resins. These resins are produced by reacting epoxy resin
with acrylic or methacrylic acid. This provides an unsaturated site,
much like that produced in polyester resins when maleic anhydride
is used. The resulting material is dissolved in styrene to yield a liquid
that is similar to polyester resin. Vinyl esters are also cured with the
conventional organic peroxides used with polyester resins. Vinyl
esters offer mechanical toughness and excellent corrosion resistance.
These enhanced properties are obtained without complex processing,
handling or special shop fabricating practices that are typical with
epoxy resins.
Phenolic
Phenolics are a class of resins commonly based on phenol (carbolic
acid) and formaldehyde. Phenolics are a thermosetting resin that
cure through a condensation reaction producing water that should
be removed during processing. Pigmented applications are limited
to red, brown or black. Phenolic composites have many desirable
performance qualities including high temperature resistance,
creep resistance, excellent thermal insulation and sound damping
properties, corrosion resistance and excellent fire/smoke/smoke
toxicity properties. Phenolics are applied as adhesives or matrix
binders in engineered woods (plywood), brake linings, clutch plates,
circuit boards and more.
Composite’s properties depend on:
• fibre content (volume fraction)
• fibre alignment (unidirectional gives highest value)
• fibre length (discontinuous OK if l/d > 30)
• fibre distribution
• fibre orientation; multi-axial loads (lay-up, stacking sequence)
Benefits of using composites
superior mechanical properties compared to the matrix
low density – weight saving
corrosion resistance
fatigue
expansion coefficient
2.5 Stress-strain curves for a selection of fibres 2.6 Directionality of fibres2.4 Young’s Modulus-Density graph

30. 30
Polyurethane
Polyurethane is a family of polymers with widely
ranging properties and uses, all based on the
exothermic reaction of an organic polyisocyanates
with a polyols (an alcohol containing more than one
hydroxl group). A few basic constituents of different
molecular weights and functionalities are used
to produce the whole spectrum of polyurethane
materials. The versatility of polyurethane chemistry
enables the polyurethane chemist to engineer
polyurethane resin to achieve the desired properties.
Polyurethanes appear in an amazing variety of forms.
These materials are all around us, playing important
roles in more facets of our daily life than perhaps
any other single polymer. They are used as a coating,
elastomer, foam, or adhesive. When used as a
coating in exterior or interior finishes, polyurethane’s
are tough, flexible, chemical resistant, and fast
curing. Polyurethanes as an elastomer have superior
toughness and abrasion is such applications as solid
tires, wheels, bumper components or insulation.
There are many formulations of polyurethane foam
to optimize the density for insulation, structural
sandwich panels, and architectural components.
Polyurethanes are often used to bond composite
structures together. Benefits of polyurethane
adhesive bonds are that they have good impact
resistance, the resin cures rapidly and the resin
bonds well to a variety of different surfaces such as
concrete.
Thermoplastics
A thermoplastic is a polymer that turns to a liquid
when heated and freezes to a very glassy state when
cooled sufficiently. Most thermoplastics are high-
molecular-weight polymers whose chains associate
through weak Van der Waals forces (polyethylene);
stronger dipole-dipole interactions and hydrogen
bonding (nylon); or even stacking of aromatic
rings (polystyrene). Thermoplastic polymers differ
from thermosetting polymers (Bakelite; vulcanized
rubber) as they can, unlike thermosetting polymers,
be remelted and re-moulded.
Thermoplastics are elastic and flexible above a glass
transition temperature Tg, specific for each one—
the midpoint of a temperature range in contrast to
the sharp melting point and melting point of a pure
crystalline substance like water. Below a second,
higher melting temperature, Tm, also the midpoint
of a range, most thermoplastics have crystalline
regions alternating with amorphous regions in
which the chains approximate random coils. The
amorphous regions contribute elasticity and the
crystalline regions contribute strength and rigidity,
as is also the case for non-thermoplastic fibrous
proteins such as silk.
Thermoplastics can go through melting/freezing
cycles repeatedly and the fact that they can be
reshaped upon reheating gives them their name.
This quality makes thermoplastics recyclable. [2.7]
2.7 Close-up of a glass fibre mat

31. 31
The primary function of fibers or reinforcements is to carry load along the length
of the fiber to provide strength and stiffness in one direction. Reinforcements can
be oriented to provide tailored properties in the direction of the loads imparted
on the end product. Reinforcements can be both natural (Appendix) and man-
made. Many materials are capable of reinforcing polymers. Some materials, such
as the cellulose in wood, are naturally occurring products. Most commercial
reinforcements, however, are man-made. Of these, by far the largest volume
reinforcement measured either in quantity consumed or in product sales, is glass
fiber. Other composite reinforcing materials include carbon, aramid, UHMW (ultra
high molecular weight) polyethylene, polypropylene, polyester and nylon. Carbon
fiber is sometimes referred to as graphite fiber.The distinction is not important in an
introductorytext,butthedifferencehastodowiththerawmaterialandtemperature
at which the fiber is formed. More specialized reinforcements for high strength and
high temperature use include metals and metal oxides such as those used in aircraft
or aerospace applications.
Development of Reinforcements - Fibers
Early in the development of composites, the only reinforcements available were
derived from traditional textiles and fabrics. Particularly in the case of glass fibers,
experience showed that the chemical surface treatments or “sizings” required to
process these materials into fabrics and other sheet goods were detrimental to the
adhesion of composite polymers to the fiber surface. Techniques to remove these
materials were developed, primarily by continuous or batch heat cleaning. It was
then necessary to apply new “coupling agents” (also known as finishes or surface
treatments), an important ingredient in sizing systems, to facilitate adhesion of
polymers to fibers, particularly under wet conditions and fiber processing.
Most reinforcements for either thermosetting or thermoplastic resins receive some
form of surface treatments, either during fiber manufacture or as a subsequent
treatment. Other materials applied to fibers as they are produced include resinous
binders to hold fibers together in bundles and lubricants to protect fibers from
degradation caused by process abrasion. [2.8]
Glass Fibers
Based on an alumina-lime-borosilicate composition, “E” glass produced fibers are
considered the predominant reinforcement for polymer matrix composites due to
their high electrical insulating properties, low susceptibility to moisture and high
mechanical properties. Other commercial compositions include “S” glass, with
higher strength, heat resistance and modulus, as well as some specialized glass
reinforcements with improved chemical resistance, such as AR glass (alkali resistant).
Glass fibers used for reinforcing composites generally range in diameter from 9 to 23
microns. Fibers are drawn at high speeds, approaching 200 miles per hour, through
small holes in electrically heated bushings. These bushings form the individual
filaments. The filaments are gathered into groups or bundles called “strands.” The
filaments are attenuated from the bushing, water and air cooled, and then coated
with a proprietary chemical binder or sizing to protect the filaments and enhance
the composite laminate properties. The sizing also determines the processing
characteristics of the glass fiber and the conditions at the fiber-matrix interface in
the composite.
Glass is generally a good impact resistant fiber but weighs more than carbon or
aramid. Glass fibers have excellent characteristics, equal to or better than steel in
certain forms. The lower modulus requires special design treatment where stiffness
is critical. Composites made from this material exhibit very good electrical and
thermal insulation properties. Glass fibers are also transparent to radio frequency
radiation and are used in radar antenna applications.
Carbon Fibers
Carbon fiber is created using polyacrylonitrile (PAN), pitch or rayon fiber precursors.
PAN based fibers offer good strength and modulus values up to 85-90 Msi. They
also offer excellent compression strength for structural applications up to 1000
ksi. Pitch fibers are made from petroleum or coal tar pitch. Pitch fibers extremely
high modulus values (up to 140 Msi) and favorable coefficient of thermal expansion
make them the material used in space/satellite applications. Carbon fibers are more
expensive than glass fibers, however carbon fibers offer an excellent combination of
strength, low weight and high modulus. The tensile strength of carbon fiber is equal
to glass while its modulus is about three to four times higher than glass.
Carbon fibers are supplied in a number of different forms, from continuous filament
tows to chopped fibers and mats. The highest strength and modulus are obtained
by using unidirectional continuous reinforcement. Twist-free tows of continuous
filament carbon contain 1,000 to 75,000 individual filaments, which can be woven
or knitted into woven roving and hybrid fabrics with glass fibers and aramid fibers.
Carbon fiber composites are more brittle (less strain at break) than glass or aramid.
Carbon fibers can cause galvanic corrosion when used next to metals. A barrier
material such as glass and resin is used to prevent this occurrence. [2.9]
Aramid Fibers (Polyaramids)
Aramid fiber is an aromatic polyimid that is a man-made organic fiber for composite
reinforcement. Aramid fibers offer good mechanical properties at a low density
with the added advantage of toughness or damage/impact resistance. They are
characterized as having reasonably high tensile strength, a medium modulus, and
a very low density as compared to glass and carbon. The tensile strength of aramid
fibers are higher than glass fibers and the modulus is about fifty percent higher than
glass.Thesefibersincreasetheimpactresistanceofcompositesandprovideproducts
with higher tensile strengths. Aramid fibers are insulators of both electricity and
heat. They are resistant to organic solvents, fuels and lubricants. Aramid composites
are not as good in compressive strength as glass or carbon composites. Dry aramid
fibers are tough and have been used as cables or ropes, and frequently used in
ballistic applications.
Reinforcements

32. 32
Regardless of the material, reinforcements are available in forms to serve a
wide range of processes and end-product requirements. Materials supplied
as reinforcement include roving, milled fiber, chopped strands, continuous,
choppedorthermoformablemat.Reinforcementmaterialscanbedesigned
with unique fiber architectures and be preformed (shaped) depending on
the product requirements and manufacturing process.
Multi-End and Single-End Rovings
Rovings are utilized primarily in thermoset compounds, but can be utilized
in thermoplastics. Multi-end rovings consist of many individual strands or
bundles of filaments, which are then chopped and randomly deposited
into the resin matrix. Processes such as sheet molding compound (SMC),
preform and spray-up use the multi-end roving. Multi-end rovings can
also be used in some filament winding and pultrusion applications. The
single-end roving consists of many individual filaments wound into
a single strand. The product is generally used in processes that utilize a
unidirectional reinforcement such as filament winding or pultrusion.
Mats
Reinforcing mats are usually described by weight-per-unit-of-area. The
type and amount of binder that is used to hold the mat together dictate
differences between mat products. In some processes such as hand lay-up,
it is necessary for the binder to dissolve. In other processes, particularly in
compression molding, the binder must withstand the hydraulic forces and
the dissolving action of the matrix resin during molding. Therefore, two
general categories of mats are produced and are known as soluble and
insoluble.
Woven, Stitched, Braided Fabrics
There are many types of fabrics that can be used to reinforce resins in a
composite. Multidirectional reinforcements are produced by weaving,
knitting, stitched or braiding continuous fibers into a fabric from twisted
and plied yarn. Fabrics refer to all flat-sheet, roll goods, whether or not
they are strictly fabrics. Fabrics can be manufactured utilizing almost any
reinforcing fiber.The most common fabrics are constructed with fiberglass,
carbon or aramid. Fabrics are available in several weave constructions and
thickness (from 0.0010 to 0.40 inches). Fabrics offer oriented strengths and
high reinforcement loadings often found in high performance applications.
Fabrics are typically supplied on rolls of 25 to 300 yards in length and 1
to 120 inches in width. The fabric must be inherently stable enough to be
handled, cut and transported to the mold, but pliable enough to conform
to the mold shape and contours. Properly designed, the fabric will allow
for quick wet out and wet through of the resin and will stay in place once
the resin is applied. Fabrics, like rovings and chopped strands, come with
specific sizings or binder systems that promote adhesion to the resin
system. [2.10]
Fabrics allow for the precise placement of the reinforcement. This cannot
be done with milled fibers or chopped strands and is only possible with
continuous strands using relatively expensive fiber placement equipment.
Due to the continuous nature of the fibers in most fabrics, the strength to
weight ratio is much higher than that for the cut or chopped fiber versions.
Stitched fabrics allow for customized fiber orientations within the fabric
structure. This can be of great advantage when designing for shear or
torsional stability.
Woven fabrics are fabricated on looms in a variety of weights, weaves, and
widths. In a plain weave, each fill yarn or roving is alternately crosses over
and under each warp fiber allowing the fabric to be more drapable and
conform to curved surfaces. Woven fabrics are manufactured where half
of the strands of fiber are laid at right angles to the other half (0o
to 90o
).
Woven fabrics are commonly used in boat manufacturing. [2.11]
Stitched fabrics, also known as non-woven, non-crimped, stitched, or
knitted fabrics have optimized strength properties because of the fiber
architecture. Woven fabric is where two sets of interlaced continuous
fibers are oriented in a 0o
and 90o
pattern where the fibers are crimped
and not straight. Stitched fabrics are produced by assembling successive
layers of aligned fibers. Typically, the available fiber orientations include
the 0o
direction (warp), 90o
direction (weft or fill), and +45o
direction (bias).
Woven Fabrics (2-D weaving)
Genrally more expensive than UD tapes
but significant cost savings during
manufacturing
fabrics are generally described according
to the types of weave and the number of
yarns per inch – first in the warp direction
(parallel to length of fabric) and then in the
fill (or weft) direction (perpendicular to the
warp)
Unidirectional Fabric
warp strands are as straight as tape
improved drapability over tape
minimal reduction of fibre strength
improved fibre alignment
Plain Weave Fabric
some loss of properties due to fibre
crimping
provides reproducible laminate thickness
good drapability
speedier lay-up
easier to handle
wet-out difficulties with tightly woven
fabrics
width limitations
thicker than tape
good damage tolerance
Advantages:
enhanced toughness (fewer layers, kinked
fibres deflect interlaminar cracking)
damage tolerant due to fibre-interlocking
convenience of handling
no weak transverse direction
superior drapability of some weaves
Disadvantages:
more expensive (based on 3K tow to
ensure a thin uniform sheet – 6K and 12K
tows typical in UD tape)
involve additional manufacturing -
weaving
kinked fibres limit full strength potential
lower fibre volume fraction than ud tape
fabric distortion (bowing and skewing)
causes part warpage
Economic aspects
Composite materials are expensive:
design costs are higher
higher cost of analysis
higher cost of component testing
certification and documentation testing
but
costs may be lowered by innovative design concepts which consider manufacturing
lower part count
reduction in number of fasteners used
use of automationReinforcement Forms

33. 33
The assembly of each layer is then sewn together. This type of
construction allows for load sharing between fibers so that a
higher modulus, both tensile and flexural, is typically observed.
The fiber architecture construction allows for optimum resin flow
when composites are manufactured. These fabrics have been
traditionally used in boat hulls for 50 years. Other applications
include light poles, wind turbine blades, trucks, busses and
underground tanks. These fabrics are currently used in bridge
decks and column repair systems. Multiple orientations provide a
quasi-isotropic reinforcement.
Braided fabrics are engineered with a system of two or more yarns
intertwined in such a way that all of the yarns are interlocked for
optimum load distribution. Biaxial braids provide reinforcement
in the bias direction only with fiber angles ranging from ± 15o
to ±
95o
.Triaxial braids provide reinforcement in the bias direction with
fiber angles ranging from ± 10o
to ± 80o
and axial (0o
) direction.
Unidirectional
Unidirectional reinforcements include tapes, tows, unidirectional
tow sheets and rovings (which are collections of fibers or strands).
Fibers in this form are all aligned parallel in one direction and
uncrimped providing the highest mechanical properties.
Composites using unidirectional tapes or sheets have high
strength in the direction of the fiber. Unidirectional sheets are thin
and multiple layers are required for most structural applications.
In some composite designs, it may be necessary to provide a
corrosion or weather barrier to the surface of a product. A surface
veil is a fabric made from nylon or polyester that acts as a very
thin sponge that can absorb resin to 90% of its volume. This helps
to provide an extra layer of protective resin on the surface of the
product. Surface veils are used to improve the surface appearance
and insure the presence of a corrosion resistance barrier for typical
composites products such as pipes, tanks and other chemical
process equipment. Other benefits include increased resistance
to abrasion, UV and other weathering forces. Veils may be used in
conjunction with gel coats to provide reinforcement to the resin.
Prepreg
Prepregs are a ready-made material made of a reinforcement form
and polymer matrix. Passing reinforcing fibers or forms such as
fabrics through a resin bath is used to make a prepreg. The resin is
saturated (impregnated) into the fiber and then heated to advance
the curing reaction to different curing stages. Thermoset or
thermoplastic prepregs are available and can be either stored in a
refrigerator or at room temperature depending on the constituent
materials. Prepregs can be manually or mechanically applied at
various directions based on the design requirements. [2.11]
Impact – composites are very susceptible to impact damage.
Impact damage :
caused by dropped tools, runway debris, hail or bird impact damage, bal-
listics.
more critical in compressively loaded structures
BVID and CAI
damage tolerance may be improved by:
minimising grouping of plies of same orientation
using more ±45° plies (soft skin design)
using ±45° plies on the outer surfaces
thermoplastics
2.9 Woven fabrics
2.8 Impact Damage

34. 34
An optical fiber (or fibre) is a glass or plastic fiber that carries light
along its length. Fiber optics is the overlap of applied science
and engineering concerned with the design and application
of optical fibers. Optical fibers are widely used in fiber-optic
communications, which permits transmission over longer
distances and at higher bandwidths (data rates) than other
forms of communications. Fibers are used instead of metal wires
because signals travel along them with less loss, and they are also
immune to electromagnetic interference. Fibers are also used for
illumination, and are wrapped in bundles so they can be used
to carry images, thus allowing viewing in tight spaces. Specially
designed fibers are used for a variety of other applications,
including sensors and fiber lasers. [2.12, 2.14]
Light is kept in the core of the optical fiber by total internal
reflection. This causes the fiber to act as a waveguide. Fibers
which support many propagation paths or transverse modes
are called multi-mode fibers (MMF), while those which can only
support a single mode are called single-mode fibers (SMF). Multi-
mode fibers generally have a larger core diameter, and are used
for short-distance communication links and for applications
where high power must be transmitted. Single-mode fibers are
used for most communication links longer than 550 metres
History
Fiber optic technology experienced a phenomenal rate of
progress in the second half of the twentieth century. Early
success came during the 1950’s with the development of the
fiberscope. This image-transmitting device, which used the
first practical all-glass fiber, was concurrently devised by Brian
O’Brien at the American Optical Company and Narinder Kapany
(who first coined the term ‘fiber optics’ in 1956) and colleagues
at the Imperial College of Science and Technology in London.
Early all-glass fibers experienced excessive optical loss, the loss
of the light signal as it traveled the fiber, limiting transmission
distances.
This motivated scientists to develop glass fibers that included
a separate glass coating. The innermost region of the fiber, or
core, was used to transmit the light, while the glass coating,
or cladding, prevented the light from leaking out of the core
by reflecting the light within the boundaries of the core. This
concept is explained by Snell’s Law which states that the angle
at which light is reflected is dependent on the refractive indices
of the two materials‘ in this case, the core and the cladding. The
lower refractive index of the cladding (with respect to the core)
causes the light to be angled back into the core.
The fiberscope quickly found application inspecting welds
inside reactor vessels and combustion chambers of jet aircraft
engines as well as in the medical field. Fiberscope technology
has evolved over the years to make laparoscopic surgery one of
the great medical advances of the twentieth century.
The development of laser technology was the next important
step in the establishment of the industry of fiber optics. Only
the laser diode (LD) or its lower-power cousin, the light-emitting
diode (LED), had the potential to generate large amounts of light
in a spot tiny enough to be useful for fiber optics. In 1957, Gordon
Gould popularized the idea of using lasers when, as a graduate
student at Columbia University, he described the laser as an
intense light source. Shortly after, Charles Townes and Arthur
Schawlow at Bell Laboratories supported the laser in scientific
circles. Lasers went through several generations including the
development of the ruby laser and the helium-neon laser in 1960.
Semiconductor lasers were first realized in 1962; these lasers are
the type most widely used in fiber optics today.
Because of their higher modulation frequency capability, the
importance of lasers as a means of carrying information did
not go unnoticed by communications engineers. Light has an
information-carrying capacity 10,000 times that of the highest
radio frequencies being used. However, the laser is unsuited
for open-air transmission because it is adversely affected by
environmental conditions such as rain, snow, hail, and smog.
Faced with the challenge of finding a transmission medium
other than air, Charles Kao and Charles Hockham, working at
the Standard Telecommunication Laboratory in England in
1966, published a landmark paper proposing that optical fiber
Sensing
conductive paste
optical fiber
inner core
outer core 1.5cm
125μm
635μm
Fibre Optics
2.10 Diagram of a fibre optic cable
2.11 Fibre optic cables

35. 35
might be a suitable transmission medium if its attenuation
could be kept under 20 decibels per kilometer (dB/km). At
the time of this proposal, optical fibers exhibited losses of
1,000 dB/ km or more. At a loss of only 20 dB/km, 99% of the
light would be lost over only 3,300 feet. In other words, only
1/100th of the optical power that was transmitted reached
the receiver. Intuitively, researchers postulated that the
current, higher optical losses were the result of impurities in
the glass and not the glass itself. An optical loss of 20 dB/
km was within the capability of the electronics and opto-
electronic components of the day.
Intrigued by Kao and Hockham’s proposal, glass researchers
began to work on the problem of purifying glass. In 1970,
Drs. Robert Maurer, Donald Keck, and Peter Schultz of
Corning succeeded in developing a glass fiber that exhibited
attenuation at less than 20 dB/km, the threshold for making
fiber optics a viable technology. It was the purest glass ever
made. [2.16]
The early work on fiber optic light source and detector was
slow and often had to borrow technology developed for
other reasons. For example, the first fiber optic light sources
were derived from visible indicator LEDs. As demand grew,
light sources were developed for fiber optics that offered
higher switching speed, more appropriate wavelengths, and
higher output power. For more information on light emitters
see Laser Diodes and LEDs.
Fibre Optic Sensors
Most people, incorrectly, assume fibre optic cables are only
used for telecommunication purposes; there are actually
many other uses for fibre optic cables. While telecommuni-
cations is a very common, visible, use of fibre optics, it is also
very common to use them as sensors. [2.15]
Because of the various properties of light, all of which also
occur within a fibre optic cable, fibre optics can be used to
measure strain, temperature, or pressure. This can happen
by designing a fibre optic cable to be sensitive to a specific
element. This will then affect the light pulse sent through
the fibre optic cable, the change pulse received after pass-
ing through the fibre can then be analyzed to determine the
amount of strain or the temperature, or whatever is being
measured. This can be advantageous due to the fact that no
electricity passes through the cable; in some sensitive envi-
ronments this is a necessity.
There are a variety of fiber optic sensors. These can be clas-
sified as follows.
A) Based on the modulation and demodulation process a
sensor can be called as an intensity (amplitude), a phase, a
frequency, or a polarization sensor. Since detection of phase
or frequency in optics calls for interferometric techniques,
the latter is also termed as an interferometric sensor. From
a detection point of view the interferometeric technique im-
plies heterodyne detection/coherent detection. On the oth-
er hand intensity sensors are basically incoherent in nature.
Intensity or incoherent sensors are simple in construction,
while coherent detection (interferometric) sensors are more
complex in design but offer better sensitivity and resolution.
B) Fiber optic sensors can also be classified on the basis of
their application: physical sensors (e.g. measurement of tem-
perature, stress, etc.); chemical sensors (e.g. measurement of
pH content, gas analysis, spectroscopic studies, etc.); bio-
medical sensors (inserted via catheters or endoscopes which
measure blood flow, glucose content and so on). Both the
intensity types and the interferometric types of sensors can
be considered in any of the above applications.
C) Extrinsic or intrinsic sensors is another classification
scheme. In the former, sensing takes place in a region out-
side of the fiber and the fiber essentially serves as a conduit
for the to-and-fro transmission of light to the sensing region
efficiently and in a desired form. On the other hand, in an
intrinsic sensor one or more of the physical properties of the
fiber undergo a change as mentioned in A above.
Extrinsic Fibre Optic Sensors
Linear and
angular
position
Pressure
Flow
Damage
Liquid Level
Pressure
Pressure
Accoustics
Vibration
Temperature
Viscosity
Chemical analysis
TemperaturePressure
Acceleration
Vibration
Rotary position
TemperatureFlowTemperature
Strain
Encoder
Plates/ Disks
Reflection and
transmission
Total Internal
Reflection
Gratings Fluorescence
Evanescent
Laser Doppler
Velocimetry
Absorption
Band Edge
Photoelastic
Effects Pyrometers
Strain
Pressure
Vibration
Temperature Rotation
Acceleration
Acoustics
Magnetic Fields
Electric Fields
Strain
Temperature
Pressure
Current
Acoustic
Acceleration
Strain
Magnetic field
Temperature
Temperature
Strain
Pressure
TemperatureTemperature
Strain
Microbend
Sensors
Distributed
Sensors
Blackbody
Sensors
Interferometric
Sensors
Rayleigh Raman
Mode
Coupling
Quasi-
distributed
Intrinsic Fibre Optic Sensors
2.12 Classification of Fibre Optic Sensors

36. 36
Fiber optic sensors are used in many ways. The most
common are:
1. Monitor the manufacturing process of composite
strucures.
2. Check out the performance of any part or point of
the structure during assembly.
3. Form a sensor network and serve as a health moni-
toring and performance evaluation system during the
operational period of the structure. [2.15]
Current applications
1. Processcure monitoring of composites
Due to advantages such as high strength-to-weight ra-
tios, good fatigue and corrosion resistance and flexibil-
ity to tailor mechanical properties, composite materials
find application in many industries including aircraft,
automobile, building and container industries. One im-
portantissueintheiruseistheneedtodemonstratethe
reliability of composite structural members . To assure
on this score it is necessary to evaluate the effects of
impact damage, environmental effects and/or process-
ing defects. Nondestructive evaluation of the above is
both costly and time consuming. If sensors can be di-
rectly integrated into composite materials it will help
monitor the internal state of the composite structural
members and reduce the uncertainty and doubts as
regards the status of the material. Such integrated sen-
sors can generate quantitative data which will indicate
the state of the cure of an epoxy matrix resin initially
and later continuously monitor the in-service condi-
tion. Fourier Transform Infrared (FTIR), ultrasonic meas-
urements and fluorescence spectroscopy are some of
the known methods used in cure sensing. A fiber optic
combined cure and in-service strain sensor was report-
ed recently by May et al[ ]. The cure state is monitored
on the basis of refractive index changes due to cross
linking when the curing takes place while continuous
strain monitoring during service is achieved using a
Fabry-Perot Interferometric (FPI) technique. The com-
bined sensor is embedded into the composite during
fabrication. The sensor is as shown in fig.6. [2.15]
2.Applications in civil engineering
Using a microbend sensor as shown in fig.8, pressure,
load and displacement measurements can be made
on civil structures such buildings and bridges. Such a
sensor is attractive because it is simple to use, low cost
and very rugged. Initial calibration could be done with
a compression testing machine.
Advantages of Fibre Optic Sensors
• Passive (all dielectric)
• Light-weight
• Small size
• Immunity to electromagnetic interference
• High-temperature performance
• Large bandwidth
• Environmental ruggedness to vibration and shock
• High sensitivity
• Electrical and optical multiplexing
2.13 Digital Microscope image of a
fibre optic sensor
2.14 Fibre Optic Sensor Structure
2.15 Fibre Optic Cable

37. 37
2.16 Fibre Optic Cables

38. 38
A thermocouple (or thermocouple
thermometer) is a junction between two
different metals that produces a voltage
related to a temperature difference.
Thermocouples are a widely used type of
temperature sensor and can also be used
to convert heat into electric power.
Any circuit made of dissimilar metals will
produce a temperature-related potential.
Thermocouplesforpracticalmeasurement
of temperature are made of specific alloys,
which in combination have a predictable
and repeatable relationship between
temperature and voltage. Particular alloys
are used for different temperature ranges.
Other properties, such as resistance to
corrosion, may also be important when
choosing which type of thermocouple is
most appropriate for a given application.
Where the measurement point is far
from the measuring instrument, the
intermediate connection can be made
by extension wires, which are less costly
than the materials used to make the
sensor. Thermocouples are standardized
against a reference temperature of 0
degrees Celsius; practical instruments
use electronic methods of cold-
junction compensation to adjust for
varying temperature at the instrument
terminals. Electronic instruments can also
compensateforthevaryingcharacteristics
of the thermocouple, and so improve the
precision and accuracy of measurements.
[2.19, 2.20]
Type
Temperature range °C
(continuous)
Temperature range °C
(short term)
Tolerance class one (°C) Tolerance class two (°C)
IEC Color
code
BS Color
code
ANSI
Color
code
K 0 to +1100 −180 to +1300
±1.5 between −40 °C and 375 °C
±0.004×T between 375 °C and 1000 °C
±2.5 between −40 °C and 333 °C
±0.0075×T between 333 °C and 1200 °C
J 0 to +700 −180 to +800
±1.5 between −40 °C and 375 °C
±0.004×T between 375 °C and 750 °C
±2.5 between −40 °C and 333 °C
±0.0075×T between 333 °C and 750 °C
N 0 to +1100 −270 to +1300
±1.5 between −40 °C and 375 °C
±0.004×T between 375 °C and 1000 °C
±2.5 between −40 °C and 333 °C
±0.0075×T between 333 °C and 1200 °C
R 0 to +1600 −50 to +1700
±1.0 between 0 °C and 1100 °C
±[1 + 0.003×(T − 1100)] between 1100 °C and 1600 °C
±1.5 between 0 °C and 600 °C
±0.0025×T between 600 °C and 1600 °C
Not
defined.
S 0 to 1600 −50 to +1750
±1.0 between 0 °C and 1100 °C
±[1 + 0.003×(T − 1100)] between 1100 °C and 1600 °C
±1.5 between 0 °C and 600 °C
±0.0025×T between 600 °C and 1600 °C
Not
defined.
B +200 to +1700 0 to +1820 Not Available ±0.0025×T between 600 °C and 1700 °C
No standard
use copper
wire
No standard
use copper
wire
Not
defined.
T −185 to +300 −250 to +400
±0.5 between −40 °C and 125 °C
±0.004×T between 125 °C and 350 °C
±1.0 between −40 °C and 133 °C
±0.0075×T between 133 °C and 350 °C
E 0 to +800 −40 to +900
±1.5 between −40 °C and 375 °C
±0.004×T between 375 °C and 800 °C
±2.5 between −40 °C and 333 °C
±0.0075×T between 333 °C and 900 °C
Chromel/AuFe −272 to +300 n/a Reproducibility 0.2% of the voltage; each sensor needs individual calibration.
Thermocouples
2.17 Thermocouple
2.18 Thermocouple Types

39. 39
A strain gauge is a resistance-based sensor used by
mechanical engineers to measure strain in an object.
Strain is defined as the change in length of a component
divided by the length of a component. Strain, therefore,
does not officially have a unit of measurement, but for
reference purposes, the unit of “strain” is used. Because
the changes in length are often very small, the unit of
microstrain, or strain times 10 to the 6th power, is often
used.
A strain gauge is the primary sensor type used to measure
strain. The primary type of strain gauge is a metal foil
gauge. A strain gauge consists of a long thin “wire” of
metal foil that is wrapped back and forth across a grid,
called a matrix. The matrix is attached to a thin flexible
backing material with an adhesive, often a cyanoacrylate.
The strain gauge is bonded to the part to be evaluated,
and the matrix is oriented in the direction of the applied
strain. The strain exerted in the part is also exerted on
the strain gauges, and the wire that makes up the matrix
stretches or compresses.
Strain Gauge Configurations
Strain gauges are available in a wide variety of sizes in a
wide variety of sizes and configurations, depending on
the material and geometry of the part to be tested and
the expected strain levels. Matrix lengths can vary from a
few millimeters to several inches.
While one strain gauge measures strain along a single
axis, multiple strain gauge matrices can be combined
into a single sensor. The most common multiple matrix
configuration is the bi-axial strain gauge. In this case,
two individual strain gauges are oriented at a right angle,
with their axes passing through a common point. Other
multiplematrixorientationsincludegaugesformeasuring
shear strain, residual stresses, and hole stresses.
Strain Gauge Functionality
A strain gauge is a resistive sensor. A voltage is passed
through the wire, and any variation in resistance is
calculated based on a measured voltage. If the part is
compressed, the wire that makes up the strain gauge
matrix is compressed, and its cross-section area increases.
This reduces the resistance of the wire. If the part is
stretched, the wire that makes up the strain gauge matrix
is compressed, and its cross-sectional area decreases.
This increases the resistance of the gauge. In these terms,
if tensile strain is considered positive, then resistance is
proportional to strain. The measured voltage is converted
to strain using a circuit called a Wheatstone Bridge.
Temperature Compensation
Active-Dummy Method
The active-dummy method uses the 2-gage system where
an active gage, A, is bonded to the measuring object and
a dummy gage, D, is bonded to a dummy block which is
free from the stress of the measuring object but under
the same temperature condition as that affecting the
measuring object.
The dummy block should be made of the same material
as the measuring object. As shown in Fig. , the two gages
are connected to adjacent sides of the bridge. Since
the measuring object and the dummy block are under
the same temperature condition, thermally-induced
elongation or contraction is the same on both of them.
Thus, gages A and B bear the same thermally-induced
strain, which is compensated to let the output, e, be zero
because these gages are connected to adjacent sides.
[2.21, 2.22, 2.23]
Strain Gauges
2.19 Installation of a strain gauge
2.20 Strain gauge
2.22 Strain Gauge Structure2.21 Strain Gauge Half-Bridge Configuration

40. 40
Shape Memory Alloys
The Shape Memory Effect is the ability of a material to remember
the shape it had above a certain characteristic temperature, even
though it has been deformed severely at a lower temperature
(below the characteristic). The material, after being deformed
at the lower temperature, recovers its original shape on being
heated to the characteristic temperature.
Shape Memory Alloys (SMAs) are a group of metallic materials
that demonstrate the Shape Memory Effect. There has been a
considerable interest in the recent years in developing shape
memoryalloyactuatorsbecauseoftheiradvantagesinproducing
large plastic deformations, high force-to-weight ratio and low
driving voltages.
We can distinguish two types of the Memory Effect. The
Mechanical Memory Effect is initiated through an external force
and leads to huge elastic strains of the alloy.TheThermal Memory
Effect occurs upon heating of a Memory metal, which has been
previously deformed plastically. A high specific mechanical work
is generated.
Both effects can be achieved in the same alloy by special
thermomechanical treatment. This special metallurgical
treatment gives the alloys their particular properties and is of
high importance for the success of the respective application.
One-Way Shape Memory Effect
This specific temperature is related to a martensitic phase
transition. The terms ‘austenite’ and ‘martensite’ are used in a
generic sense for the higher-temperature phase and the lower-
temperature phase, respectively. The SME arises primarily due
to the accommodative reorientation of the austenitic and the
martensitic phases. []
Superelasticity is the ability of a material to be able to undergo
large but recoverable strains, provided the deformation is carried
out in a characteristic range of temperatures. This property
is an example of a purely field-induced phase transition (at a
fixed temperature). When the deforming stress is applied at a
temperature (within the characteristic temperature range) at
which it is in the austenitic phase, the stress sends the material to
the martensitic phase, with an accompanying large deformation.
When the stress is removed, the material recovers its shape
because it reverts back to the austenitic phase.
A typical shape-memory cycle runs as follows, assuming that
the material is in the martensitic phase at room temperature.
It is first heated towards the temperature of the martensite-
austenite phase transition. Since this is typically a case of first-
order phase transition, there is a range of temperatures in which
the martensitic and the austenitic phase coexist. There is thus
a temperature As at which the austenitic phase starts forming.
Further increase of temperature converts more and more of the
martensitic phase to the austenitic phase. Finally at a certain
temperature Af, the transition is complete.
At the end of the cooling down process, the SMA usually does not
recover its original plastically deformed shape. Since the shape
is remembered only on heating and not also on cooling-down
to the martensitic phase, this is called one-way shape memory
effect.
Two-Way Shape Memory Effect
If the alloy remembers its shape in both the austenitic and the
martensitic phases, it exhibits the two-way shape memory effect.
To obtain this behavior, a specimen has to be trained. A variety
of training protocols have been described in the literature.
Most of the amount to creating a network of dislocations in the
specimen. These dislocations have an associated strain field, and
that martensitic configuration develops on cooling to the other
phase for which the overall strain energy is the least. This can
happen repeatedly across the heating and cooling cycles.
Training procedures include: repetition of the one-way SME cycle,
constrained cycling across the phase transition, thermal cycling
at constant applied stress and superelastic cycling.
[2.24, 2.28, 2.30]
2.23 One and Two Way shape memory effect
2.24 SMA light
2.25 States of a SMA
Actuation

41. 41
Heat Treating and Shape Setting
Nitinol and other shape memory alloy mill products
- bar, wire, ribbon and sheet are normally finished
by cold working to achieve dimensional control and
enhance surface quality. Cold working suppresses the
shape memory response of these alloys. It also raises
the strength and decreases the ductility. However, cold
work does not raise the stiffness of the material. Heat
treating after cold working diminishes the effects of
cold working and restores the shape memory response
of these alloys. Therefore, in order to optimize the
physical and mechanical properties of a Nitinol product
and achieve shape memory and /or superelasticity, the
material is cold worked and heat treated.
The mill product supplier normally provides the
material in the cold worked condition. The maximum
practical level of cold work will be limited by the alloy
and by the product section size. Binary superelastic
NiTi alloy fine wires with As in the range of –25 to +95°C
are typically supplied with cold reduction after the final
anneal in the range of 30 to 50%. Higher reductions are
sometimes used for very fine wires. These same alloys
will be limited to about 30% maximum cold reduction
in larger diameter bar sizes. Binary NiTi alloys with very
low As in the range of –50 to –60 °C will not sustain the
higher levels of cold work without cracking. [2.24]
Both superelastic and shape memory properties are
optimized by cold work and heat treatment. This
thermo-mechanical process is applied to all Nitinol
alloys although different amounts of cold work and
different heat treatments may be used for different
alloys and property requirements.
Shape setting is accomplished by deforming the Nitinol
to the shape of a desired component, constraining
the Nitinol by clamping and then heat treating. This
is normally done with material in the cold worked
condition, for example cold drawn wire. However,
annealed wire may be shape set with a subsequent
lower temperature heat treatment.
In shape setting cold worked material, care must be
taken to limit deformation strain to prevent cracking
of the material. Another approach is to partially anneal
the wire prior to shape setting. Yet another option is to
shapesetinincrementalsteps.Smithetal.reviewedthe
types of furnaces and fixturing hardware or mandrels
that have been used in heat treatment. Many types
of furnaces have been used including box furnaces,
continuous belt hearth furnaces, tube furnaces, heated
platen presses, vacuum furnaces, induction heaters,
salt baths and fluidized bed furnaces. The electrical
resistance of Nitinol makes it a good candidate for self
heatingbyelectriccurrent.Nitinolwillbeoxidizedwhen
heat treated in air. Therefore, surface requirements and
atmosphere control are important considerations.
[2.28]
Shape setting can be done over a wide temperature
range from 300 °C to 900°C. However, heat treating
temperatures for binary NiTi alloys are usually chosen
in the narrower range of 325 to 525°C in order to
optimize a combination of physical and mechanical
properties. Heat treating times are typically 5 minutes
to 30 minutes. Consideration must be given to the mass
of the heat treating fixture as well as the mass of the
product. Sufficient time must be allowed in the furnace
to get the entire mass to the desired temperature.
The shape setting heat treatment changes the physical
and mechanical properties of Nitinol. Morgan and
Broadly mapped the effect of temperature and time
at temperature on shape set wire properties. Their
response curves illustrate that physical and mechanical
property do not always change in the same direction.
2.26 Changes in the molecular level during shape change
NiTi Stainless Steel Titanium Ti-6Al-4V
Austenitic Martensitic
Ultimate tensile strength (Mpa) 800 - 1500 103 - 1100 483 - 1850 540 - 740 920 - 1140
Tensile yield strength (Mpa) 100 - 800 50 - 300 190 - 1213 390 830 - 1070
Modulus of elasticity (GPa) 70 - 110 21 - 69 190 - 200 105 - 110 100 - 110
Elongation at failure (%) 1 - 20 up to 60 12 - 40 16 8
*
Lowest and highest values have been compiled from picked references (Buehler l. 1967, Funakubo 1987, Breme et al. 1998, Van Humbeeck et al. 1998).
2.27 Analytical Graphs
2.28 Table of Comparison

42. 42
Properties of Nitinol
Density 6.45 gm/cm3 0.23 lb/in3
Thermal Conductivity 10 W/moK 5.78 Btu/hr ftoF
Specific Heat 322 j/kgoK 0.08 Btu/lboF
Latent Heat 24,200 J/kg 10.4 Btu/lb
Ultimate Tensile Strength 750-960 Mpa 110-140 ksi
Elongation to Failure 15.5% 15.5 %
Yield Strength (Austenite) 560 Mpa 80 ksi
Young’s Modulus (Austenite) 75 Gpa 11 Mpsi
Yield Strength (Martensite) 100 Mpa 15 ksi
Also, some properties are not monotonic
functions of time at temperature. For
example, upper plateau stress goes
through a minimum as a function of time
at temperature when heat treating a
superelastic alloy in the range of 450°C to
550°C. This can be understood in terms of
the complex precipitation response of the
nickel rich Ni – Ti alloys.
Precipitation processes in nickel rich
NiTi were studied in detail by Nishida
et al. Their TTT diagram shows that in a
Ti – 52 atomic % Ni alloy heat treated
below 820oC, precipitation starts as fine
Ti11Ni14 transitions over time to Ti2Ni3
and terminates after long time as TiNi3 in
equilibrium with the NiTi matrix. All the
while, the NiTi ratio in the matrix is being
shiftedtowardshigherTicontentandhigher
transformation temperature. Pelton et al.
reported on the combined effects of non-
isothermal and isothermal heat treatment
on the physical and mechanical properties
of Nitinol wire. This work suggests that for
a 50.8 atomic % Ni alloy Ti11Ni14 dissolves
at about 500oC and Ti2Ni3 will start to
precipitateat550oC. Thisresultsaminimum
or maximum in properties as NiTi ratio in the
matrix goes through a peak. Furthermore,
this analysis suggests that the temperature
for transition from Ti11Ni14 precipitation
to Ti2Ni3 precipitation occurs at higher
temperatures for higher Ni content alloys.
Brailovski used measurement of latent heat
measured by DSC and Vickers hardness to
map mechanical and physical properties as
a function of heat treatment. He obtained
maximum fatigue performance when the
combination of transformation temperature
and hardness were optimized.
2.29 Stress-Strain Curves
2.30 Molecular level Comparison
with Stainless Steel