Transcript Adaptive materials

Lesson 8
2014
Lesson 8
2014
 Our goal is, that after this lesson, students
are able to recognize the main groups of
adaptive materials with their typical adaptive
properties and are able to evaluate the
possibilities to utilize adaptive materials in
engineering applications.
What’s the difference between adaptive and
ordinary materials?
 Adaptive materials have properties, which can be changed
”dramatically” by different stimulus. E.g. viscosity, density,
volume, thermal or electrical conductivity can be changed in
that way.
 Properties of ”ordinary” materials do also change e.g. due to
temperature changes. E.g. viscosity changes due to
temperature, but the change is only limited, while the viscosity
of adaptive materials can be changed rapidly from solid to
liquid and vice versa.
 The stimulus to produce the “dramatic "change of selected
properties could be temperature, light, humidity, pH-value,
changes of electric or magnetic fields etc.
Briefly about the terminology
 Several terms are used with different emphasis :
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Smart materials
Intelligent materials
Active materials
Adaptive materials
Functional materials
(Adaptive) ”Material” vs. ”Surface” vs. ”Layer”
WHAT
INTELLIGENT
FEATURES
ARE
REQUIRED?
INTELLIGENT
PRODUCT
OR
SMART
MACHINE
ABILITY TO ”OBSERVE”
THE ENVIRONMENT
WHAT IS
NEEDED TO
ENABLE THESE
INTELLIGENT
FEATURES?
SENSOR
TECHNOLOGY
ABILITY TO ”MAKE DECISION”
BASED ON STIMULUS (INPUTS)
MONITORING
TECCNOLOGY
ABILITY TO ”REACT AND/OR
ADAPT” TO THE CHANGES OF
THE ENVIRONMENT
CONTROLTECHNOLOGY
ABILITY TO COMMUNICATE
WITH THE USER AND/OR
ENVIRONMENT
DATA
TRANSFER
TECHNOLOGY
UTILIZATION OF ADAPTIVE MATERIALS
Design of intelligent products
INPUT
MAIN GROUP OF
ADAPTIVE MATERIALS
EXAMPLES OF MATERIALS
PIEZOELECTRIC
MATERIALS
PZT, Quartz
MAGNETOSTRICTIVE
MATERIALS
TbFe, (TbDy)Fe, SmFe
MEMORY
MATERIALS
TiNi, TiPd
Change of the electric field
Change of the magnetic field
Change of the temperature
Coating
technology
Powder
metallurgy
Composite
structure
ADAPTIVE
MATERIALS
Nanotechnology
Chemistry
Material
science
Electrostrictive, (Piezoelectric materials)
Magnetostrictive
Strictive materials
Rheological
materials
Memory materials
Auxetic materials
Biologically active
materials
ADAPTIVE
MATERIALS
Chromogenic
materials
Phase change
materials
Piezoelectric
materials
Adaptive gels
pH-active materials
Functional
coatings
Electrorheological
Magnetorheological
Temperature shape-memory materials
Magnetic shape-memory materials
Shape-memory polymers
Crystal-based
Polymers
Fibre reinforced
Foams
Cosmetic
Medicines
Sensing applications
Photochromic
Thermochromic
Electrochromic
Solvatochromic
Lonchromic
Tribochromic
Piezochromic
Polymer gels
Conductive polymers
Insulating elastomers
Ferro-gels
Protective
Decorative
Non-reflective
Anti-adhesive
Tribologic
Anti-static
Sensors
Optical
 Piezoelectric materials are used in sensors to
measure impact forces or density (viscosity)
values of liquids.
 Piezoelectric materials are also used in quartz
clocks, electrical drums and guitars,
microphones etc.
 Piezoelectric sensors are manufactured by
powder metallurgy
 Examples of piezoelectric materials:
 Aluminium phosphate (AlPO4)
 Some fluoropolymers
 Gallium phosphate (GaPO4),
 Some ceramics (BaTiO3, KNbO3, LiNbO3,
LiTaO3, BiFeO3, NaxWO3, Ba2NaNb5O5,
Pb2KNb5O15).
 Function
 Additional measurement of
absolute pressure through
deformation of the door in a side
crash and additional sensing of
absolute pressure
 Installation
 within the side door
 Sensing principle
 Piezo-resistive, micro-mechanical
pressure sensor with highlyintegrated evaluation electronics
How to measure and evaluate adaptive
properties?
 Output strain [m/V]
 Output strain/affecting electric field strength -ratio
 Output electric field strength [Vm/N]
 Output electric field strength /affecting mechanical
stress -ratio
 Characteristic describing the change between
energy types
 = Stimulating mechanical energy/produced electric
energy -ratio (or vice versa)
 These characteristics might have different
values in different directions of the sensor
Electro- ands magnetostrictive
materials
 Electrostrictive materials strain due to the applied electric field.
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They are (unlike the piezoelectric materials) not poled.
The most prominent electrostrictive material is lead magnesium
niobate (PMN).
Magnetostrictiive materials change their length when subjected to
a magnetic field.
Magnetostrictiive materials generate a magnetic field when they are
deformed by an external force.
Magnetostrictive materials can be used for both sensors and
actuators.
Commercially-available magnetostrictive materials are based on
Terbium (Te), Iron (Fe), Dysprosium (Dy) alloys.
Magnetostrictive effects
 Joule effect :
 When subjected to an magnetic field the length of the material
will change.
 (Used in magnetostrictive actuators.)
 Villari effect:
 When a mechanical stress is imposed on a sample, there will be
a change in the magnetic flux density.
 (Used in magnetostrictive sensors.)
 Barret effect:
 The volume of the material change in response to the magnetic
field.
ELECTROSTRICTIVE
FIBRES ARE USED TO
DAMP VIBRATIONS OF
SNOWBOARDS
 When skiing at high speeds and on
tough terrain, skis tend to vibrate,
decreasing the contact area between
the snowboard edge and the snow
surface.
 This results in reduced stability and
control and decreases the skier's
speed.
 Smart snowboards overcome these
limitations by utilizing the
integration of electrostrictive sensors
and an actuator control system.
 The electrostrictive ceramics or
fibers embedded in the snowboard
convert the unwanted vibrations into
electric energy, thus keeping the
snowboard on the snow.
Magnetostrictive Villari effect is utilized in position sensors of hydraulic cylinders
Electrorheological materials
 Electrorheological (ER) materials’
 flow,
 viscosity
 damping capacity
 internal friction
 the ability to absorb energy under impact
depend on the strength of the affecting electric field.
 At high enough electric fields, the liquid materials can
solidify rapidly (in milliseconds) into viscoelastic solids.
This phenomenon is instantly reversible, if the electrical
field is removed.
 ER materials are typically fluids, gels or elastomers.
 ER materials may consist of different types of mixtures
such as silicon oxide gel, talcum powder and various
polymers with liquids such as kerosene, mineral oil,
toluene and silicone oil work.
 Some applications:
 Improvement of the vibration control characteristics of
an damping absorber using ER fluid as the working
fluid inside the absorber.
 ER fluid based application of a clutch for direct
coupling device in power transmission system of
rotating machinery.
Magnetorheological materials
 The function of magnetorheological materials (MR)is
analogic with electrorheological materials.
 At high enough magnetic fields, the liquid materials
can solidify rapidly (in milliseconds) into viscoelastic
solids. This phenomenon is instantly reversible, if the
magnetic field is removed.
 Magneto-rheological
fluid-filled dampers are
used to provide
continuously variable
real-time suspension
damping control for cars.
RHEOLOGIC MATERIALS ARE USED
E.G. IN SHOCK ABSORBERS OF
AIRCRAFTS.
Shape memory materials (SMM)
 Shape memory materials (SMMs) are featured by the
ability to recover their original shape from a significant
plastic deformation when a particular stimulus is applied.
This is known as the shape memory effect (SME).
Typically the stimulus is heat.
 Superelasticity (in alloys) or visco-elasticity (in polymers)
are also commonly observed under certain conditions.
 Most of the memory properties are based on the changes
of the crystal structures of the materials.
 An other remarkable stimulus of shape memory materials
(MSM-materials) is magnetic field.
Metallic Shape memory alloys (SMA)
 AuCd and AgCd alloys were the first memory alloys
 Three alloy systems
 NiTi-based
 Cu-based (CuAlNi , CuSn, CuZnAl)
 Fe-based
have the largest commercial importance.
 All these SMAs are thermo-responsive, i.e., the stimulus
required to trigger the shape recovery is heat (not more
than 10 degrees change of the temperature might start
the adaptive function).
 NiTi-based alloys should be the first choice if high
performance and good biocompatibility are required.
However, the manufacturing processes of NiTi-alloys
is challenging.
 Cu-based SMAs have the advantages of low
material cost and good workability in processing.
 Fe-based SMAs are used as a fastener/clamp for
one-time actuation due to the extremely low cost.
 Shape memory materials, which react to the
changes of the magnetic field are usually based on
Ni-Mn-Ga-alloys (eg. Ni2MnGa). The deformation
due to stimulus could be even 10%.
COMPARISON OF MSM MATERIALS
PZTmaterial
MSM
Ni-Mn-Ga
Electric
Magnetic
Max. strain ξ (µm/mm), linear
0.3
100
Compressive strength (MPa)
60
700
100
70
2 MV/m
400
kA/m
Control Field
Max. operating temp. (°C)
Field strength for max. strain
Shape memory polymers (SMP)
Advantages of SMPs compared to metal alloys:
 Tailoring the material properties of polymers is much easier.
 Both the material cost and the processing cost of polymers are
much lower .
 SMPs are much lighter.
 Different stimuli can be utilized: The stimulus could be heat,
UV- or infrared light, moisture or pH change.
 Many SMPs are naturally biocompatible and even
biodegradable.
Some typical materials:
 The thermoplastic polyurethane (e.g. in clothes)
 Composites with fillers based on SiC nanoparticles)
 Ni powder in a polyurethane SMP/carbon black composite.
Other shape memory materials
 Shape memory composites
 Shape memory composites (SMC), which include at least
one type of SMM, either SMA or SMP, as one of the
components
 Shape memory hybrids
 Shape memory hybrids (SMH) are made of conventional
materials.
 They are based on the dual-domain system, in which one
is the elastic domain and the other is the transition
domain, which is able to change its stiffness remarkably if
the stimulus is present.
Auxetic materials
 Auxetic materials are a special kind of materials that
exhibit negative Poisson’s ratio effect. They get fatter
when stretched and thinner when compressed.
 Auxetic behavior is can be achieved at different
structural levels from molecular to macroscopic levels.
 The internal (geometrical) structure of material plays an
important role in obtaining auxetic effect
 The behaviour of the auxetic material could be
illustrated as a desired “function of a mechanism” .
Auxetic materials
 Practical examples:
 Auxetic polyurethane (PU) foam
 Auxetic microporous PTFE
 Some forms of graphite
 Ni3Al crystals
 Carbon/epoxy, Kevlar/epoxy or Glass/epoxy composites could
have auxetic properties in a minor scale.
 Advantages:
 Adjustable strength and rigidity based on the loading direction
 Improved ware resistance
 Improved ductility of fibre reinforced composites
Principal function of auxetic materials
ORDINARY
Fpull
Fpull
Fpull
Fpull
THE
STRUCTURE
GETS
THINNER
AUXETIC
Fpull
Fpull
Fpull
Fpull
THE
STRUCTURE
GETS
THICKER
IMPROVING THE DUCTILITY OF FIBRE REINFORCED COMPOSITES
FIBRE
Fpull
Fpull
Fpull
Fpull
MATRIX
TRADITIONAL FIBRE
GETS THINNER UNDER
TENSILE LOAD
AUXETIC FIBRE GETS
THICKER UNDER
TENSILE LOAD
 Properties of the foam can be specified by defining
three independent characteristics:
 1. Pore Size
 2. Relative Density
 3. Base Material
Chromogenic materials
 Chromogenic materials are able to change
their optical properties in response to an
external stimulus such as temperature, light,
electrical current or pressure etc.
CHROMOGENIC MATERIALS
STIMULUS
Photochromic
Light
Thermochromic
Temperature
Electrochromic
Current
Solvatochromic
Polarity of liquids
Lonchromic
Ions
Tribochromic
Mechanical friction
Piezochromic
Mechanical pressure
OUTPUT
CHANGE OF THE OPTICAL MATERIAL PROPERTIES
MATERIAL GROUPS
Self darkening electrochromic rear view mirror
Photochromic sunglasses
Properties of the chromogenic material
Can be tuned either passively or actively.
Solar panel applications
Biologically active materials
 The most important material property is biocompatibility
(non-rejection property)
Applications:
 Bio-electric prosthetic nose
 Taste receptors of an electronic artificial tongue:
 Vibrotactile sensing elements for artificial skin
applications
 Artificial skin made of polymer applications like
synthetically manufactured collagens and polypeptides
 Making individually tuned “spare parts” for a human body
(like bones of ceramics)
 “So-called Tissue engineering”
Phase change materials (PCM)
 In theory when the temperature rises, the PCM melts
and the material absorbs heat. When the temperature
drops, the PCM solidifies, and heat is emitted. During the
phase change, the temperature remains constant.
 Of course ordinary materials do also absorb and emit
heat energy, but their phase remains the same.
 PCM’s capacity to absorb and emit heat energy could be
5…10 times higher compared with ordinary materials.
 Possible PCM material types: Polyethylene-paraffin
compounds, mixtures based on hydrated salts such as
CaCl2+6H2O, Na2SO4+10H2O, Na2HPO4+12H2O,
NaCO3+10H2O, and Na2S2O4+5H2O.
HEAT CAPACITY kJ/kg, ΔT 15°
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
pH-active materials
 Microcapsules embedded in a coating can detect corrosion by detecting the
pH-change caused by it and release their contents automatically to indicate,
protect, and repair damaged areas.
Adaptive gels
 Different ways to classify adaptive gels:
 Applications of adaptive polymer gels
in general
 Polymers with electric conductivity
properties
 Insulating elastomers
 Ferrogels
 The initial volume of polymer gels can be increased
1000-times larger based on stimulating pH,
temperature or electromagnetic field changes
 The size of the artificial muscle is near the size of
real human muscle (if the performance is about the
same)
 Smart gels can have either electro- or
magnetostrictive properties
 Some important polymer gels:
 - PVA
 - PAA
 - PAN
Electrostrictive gels:
 Applications of PMMA
 Ferrogels made of PVA-polymer and Fe3O4 mixture
Electrically conductive polymers:
 PAni
 PPY
 PPV
Functional coatings
 DIFFERENT MATERIAL OPTIONS: COMPOSITES , NANO OR
HYBRID COATING MATERIALS
 ADAPTIVE GENERAL SURFACE PROPERTIES
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Self-cleaning, , anti-fingerprint, antifogging, anti-icing
 ADAPTIVE PHYSICAL AND MECHANICAL PROPERTIES
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scratch resistant (CrN, TiAlN, TiC) , abrasion resistant, low-friction MoS2 PbO,
MoO3, TiO2, self-polishing, fire resistance
 ADAPTIVE BIOACTIVE PROPERTIES
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Antimicrobial, antifouling, hygienic coatings, antifungal, antioxidant
 ADAPTIVE CHEMICAL , ELECTRICAL AND THERMAL
PROPERTIES
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Anticorrosion, conductive coatings, anti-static coatings, dielectric coatings,
piezoelectric coatings, electro-magnetic shielding
 ADAPTIVE RADIATION AND OPTICAL PROPERTIES
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photochromic, thermochromic, anti-reflection