BK50A2700 Selection Criteria of Structural Materials

Lesson 82014

Selection of adaptive materials

Lesson 82014

The goal of this lesson

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.

Terminology and definitions

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.

What’s the difference between adaptive and ordinary materials?

Briefly about the terminology

Several terms are used with different emphasis :Smart materialsIntelligent materialsActive materialsAdaptive materialsFunctional materials(Adaptive) ”Material” vs. ”Surface” vs. ”Layer”

Design of intelligent products

INTELLIGENTPRODUCT

ORSMART

MACHINE

ABILITY TO ”OBSERVE” THE ENVIRONMENT

ABILITY TO ”MAKE DECISION”BASED ON STIMULUS (INPUTS)

ABILITY TO ”REACT AND/OR ADAPT” TO THE CHANGES OF

THE ENVIRONMENT

ABILITY TO COMMUNICATE WITH THE USER AND/OR

ENVIRONMENT

WHAT INTELLIGENTFEATURES

ARE REQUIRED?

WHAT IS NEEDED TO

ENABLE THESE INTELLIGENT FEATURES?

SENSOR TECHNOLOGY

MONITORING TECCNOLOGY

CONTROL-TECHNOLOGY

DATATRANSFER

TECHNOLOGY UT

ILIZ

AT

ION

OF

AD

AP

TIV

E M

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ER

IALS

INPUT

MEMORY MATERIALS

MAGNETOSTRICTIVE MATERIALS

PIEZOELECTRIC MATERIALS

Change of the electric field

Change of the magnetic field

Change of the temperature

TiNi, TiPd

TbFe, (TbDy)Fe, SmFe

PZT, Quartz

MAIN GROUP OF ADAPTIVE MATERIALS EXAMPLES OF MATERIALS

Material science

Composite structure

Powder metallurgy

ChemistryNano-

technology

Coating technology

ADAPTIVE MATERIALS

Different adaptive material groups

Piezoelectric materials

Rheological materials

Strictive materials

Memory materials

Auxetic materials

Phase change materials

Biologically active materials

Chromogenic materials

pH-active materials

Adaptive gels

Functional coatings

Electrostrictive, (Piezoelectric materials)Magnetostrictive

ElectrorheologicalMagnetorheological

Crystal-basedPolymers Fibre reinforced Foams

Cosmetic Medicines Sensing applications

PhotochromicThermochromicElectrochromicSolvatochromicLonchromicTribochromic Piezochromic

Temperature shape-memory materialsMagnetic shape-memory materialsShape-memory polymers

Protective DecorativeNon-reflectiveAnti-adhesiveTribologicAnti-static SensorsOptical

Polymer gelsConductive polymers Insulating elastomers Ferro-gels

ADAPTIVE MATERIALS

Piezoelectric materials

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 highly-integrated evaluation electronics

How to measure and evaluate adaptive properties?

Output strain [m/V] Output strain/affecting electric field strength -

ratioOutput 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

Strictive materials

Electro- ands magnetostrictive materialsElectrostrictive materials strain due to the applied electric field.

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

Rheological materials

Electrorheological materials Electrorheological (ER) materials’

flow, viscositydamping 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 materialsThe 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.

Memory materials

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-basedCu-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%.

PZT-material

MSM Ni-Mn-Ga

Control Field Electric Magnetic

Max. strain ξ (µm/mm), linear 0.3 100

Compressive strength (MPa) 60 700

Max. operating temp. (°C) 100 70

Field strength for max. strain 2 MV/m 400 kA/m

COMPARISON OF MSM MATERIALS

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 materialsShape memory compositesShape memory composites (SMC), which include at least

one type of SMM, either SMA or SMP, as one of the components

 Shape memory hybridsShape 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 materialsAuxetic 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 materialsPractical examples:

Auxetic polyurethane (PU) foamAuxetic microporous PTFESome forms of graphiteNi3Al 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 directionImproved ware resistanceImproved ductility of fibre reinforced composites

Fpull

Fpull

Fpull

Fpull

Fpull

Fpull

Fpull

Fpull THE STRUCTURE GETS THINNER

THE STRUCTURE GETS THICKER

Principal function of auxetic materials

ORDINARY

AUXETIC

Fpull Fpull

Fpull Fpull

MATRIXFIBRE

TRADITIONAL FIBRE GETS THINNER UNDER

TENSILE LOAD

AUXETIC FIBRE GETS THICKER UNDER TENSILE LOAD

IMPROVING THE DUCTILITY OF FIBRE REINFORCED COMPOSITES

Properties of the foam can be specified by defining three independent characteristics: 1. Pore Size 2. Relative Density 3. Base Material

Chromogenic materials

Chromogenic materialsChromogenic materials are able to change

their optical properties in response to an external stimulus such as temperature, light, electrical current or pressure etc.

Photochromic

Thermochromic

Electrochromic

Solvatochromic

Lonchromic

Tribochromic

Piezochromic

Light

Temperature

Current

Polarity of liquids

Ions

Mechanical friction

Mechanical pressure CH

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MATERIAL GROUPS

CHROMOGENIC MATERIALS

STIMULUS OUTPUT

Self darkening electrochromic rear view mirrorPhotochromic sunglasses

Properties of the chromogenic materialCan be tuned either passively or actively.

Solar panel applications

Biologically active materials

Biologically active materialsThe most important material property is

biocompatibility (non-rejection property)Applications:Bio-electric prosthetic noseTaste receptors of an electronic artificial tongue:Vibrotactile sensing elements for artificial skin

applicationsArtificial skin made of polymer applications like

synthetically manufactured collagens and polypeptidesMaking individually tuned “spare parts” for a human

body (like bones of ceramics)“So-called Tissue engineering”

Phase change materials

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.

WATER

STONE

WOOD

POLYM

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PHASE CHANGE M

ATERIALS

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

HE

AT

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PA

CIT

Y k

J/k

g,

ΔT

15

°

pH-active materials

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

Adaptive gelsDifferent ways to classify adaptive gels:

Applications of adaptive polymer gels in general

Polymers with electric conductivity properties

Insulating elastomersFerrogels

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 PMMAFerrogels made of PVA-polymer and Fe3O4

mixture

Electrically conductive polymers:PAni PPYPPV

Functional coatings

Functional coatingsDIFFERENT MATERIAL OPTIONS: COMPOSITES , NANO OR

HYBRID COATING MATERIALS

 

ADAPTIVE GENERAL SURFACE PROPERTIES Self-cleaning, , anti-fingerprint, antifogging, anti-icing

ADAPTIVE PHYSICAL AND MECHANICAL PROPERTIES scratch resistant (CrN, TiAlN, TiC) , abrasion resistant, low-friction MoS2 PbO, MoO3,

TiO2, self-polishing, fire resistance

ADAPTIVE BIOACTIVE PROPERTIES Antimicrobial, antifouling, hygienic coatings, antifungal, antioxidant

ADAPTIVE CHEMICAL , ELECTRICAL AND THERMAL PROPERTIES

Anticorrosion, conductive coatings, anti-static coatings, dielectric coatings, piezoelectric coatings, electro-magnetic shielding

 ADAPTIVE RADIATION AND OPTICAL PROPERTIES photochromic, thermochromic, anti-reflection