Material Charecterization

8/8/2019 Material Charecterization

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Materials characterization andtesting

HTMSTM(A)A class 2007George PopescuProf. Neil Gershenfeld

MIT Media Lab



SummaryMaterials

Introduction

States of matter and phases

Eutectics

Heat treatment

Solid mechanics

Tunable materials ( Polymers, Meta materials, Digital Materials)Active materials (Waves and Patterns)

Granular materials

CharacterizationMechanic characterization

Thermo characterization (melting point)

Optical characterization (diffraction angle)

NMR (and other resonances)

Spectroscopy

Electrical characterization



Material science



Some vocabulary

• σ : stress sensor (think : pressure)

• ε : strain sensor (think : displacement)

• E : Young modulus (scalar ? no! )• v : Poisson ration (scalar ? No !)

• ΔT : temperature change.

• k* = bulk modulus (pressure increase needed to effect agiven relative decrease in volume )

σ=EεF=-kx



States of matter

vs

phasesDifferent states of matter must be different phases

However, the reverse is not true.

The most common state of matter in the universe is plasma

Less familiar phases include•Quark-gluon plasma•Bose Einstain condensates•Fermionic condensates•Strange matter •Superfluids•Supersolids.



Plasma…



Phase transitions

first-order phase transitions :involve latent heat

second-order phase transitions :no

associated latent heat

(example : superfluid transition)

Ehrenfest classification :

First-order phase transitions exhibit a

discontinuity in the first derivative of the

free energy.

Second-order phase transitions have a

discontinuity in a second derivative of the free energy

What if derivative of free energy

diverges ?



Phases



Supercritical CO2



You thought you knew ice ?



Si/Au alloy look like this :



Eutectics



Lead/tin



Defects in Crystals



Strength vs defect density



Heat Treatment

Tradeoff between ductility and brittleness

• Annealing,

• Case hardening

• Precipitation strengthening,

• Tempering• Quenching



Tempering

The average unit cell of austenite

is, on average, a perfect little cube,

the transformation to martensite

sees this cube distorted by

interstitial carbon

atoms that do not have time to

diffuse out during displacive

transformation,

so that it is a tiny bit longer thanbefore in one dimension and a little

bit shorter

in the other two.



For this class : solids

Hooke's law :

Poisson's ratio :

F= -kx

Elasticity

ViscoelasticityPlasticityThermoelasticity



Isotropy / anisotropy : birefringence



Deformations

stress

Normal to

surface

Tangential

to surface

compression

tension

Young modulus

strain



Elastic/plastic : instantaneous



Viscoelastic : viscous deformation

Purely elastic Viscoelastic



Composites

+Matrix Materials

AsphaltPortland Cement

PolymersPolyester ResinVinyl Ester Resin

EpoxyBismaleimide

PolyimideMetals

Titanium

Ceramics

ReinforcementSteel Reinforcing Bar

Glass FibersPolymer Fibers

Nylon BasedNatural Fibers

HempCarbon Fibers

Rayon Based

Ceramic Fibers



Thermo elastic properties

the resulting strain of a material allowed to expand freely

βC is the stress per degree K in the material constrained not to expand



Engineer thermoelastic properties

Left : Optimal microstructures composedof hypothetical phases. Red is

high expansion phase, blue is low

expansion phase and white is void

a. Minimization of alpha*

b. Maximization of thermal k * for zero

thermal expansionc. Maximization of beta*

Right : Invar is blue, Nickel is red and

void is white.

c. Minimization of b*d. Maximization of contractive vertical

stress

e. Maximization of vertical strain.

Invar : Fe–36%Ni



Tunable materials

• Polymers

• Meta Materials

• Digital Materials



Polymers

organic/inorganic

Homopolymer/copolymer

Linear/branched



Epoxy

Epoxy or polyepoxide is a thermosetting polymer thatcures (polymerizes and crosslinks) when mixed with acatalyze agent or "hardener"

The oxygen on the epoxy monomers is "flipped." A matrixwith a high stress tolerance is formed, and "glues" thematerials together.





Hydrogels

Capillary forces osmotic forces



Meta Materials

• material that gains its properties from its structurerather than directly from its composition

• properties not found in naturally-formed

substances• Electromagnetism (especially optics and

photonics)

• Microwave (new types of beam steerer,modulator, band pass filter, lenses, microwavecouplers, and antenna radomes).



Negative refractive index

• ε = permittivity (how anelectric field affects and isaffected by a dielectricmedium )

• μ = permeability ( how amaterial is affected by amagnetic field)

• ε>0 μ>0 in most materials

• ε<0 μ>0 : opaque

• Engineered : ε<0 μ<0



Meta Material

Photograph of the left-handedmetamaterial (LHM) sample. The

LHM sample consists of square

copper split ring resonators and

copper wire strips on fiber glass

circuit board material. The rings

and wires are on opposite sidesof the boards, and the boards

have been cut and assembled

into an interlocking lattice.



Digital Materials

Digital

Tuneable

Active



Error reduction



Error detection

S Final 5ns 2 n s

Measured sizeExpectedsize

Standard deviation



Error tolerance



Tuneability



Active materials

• Piezzoelectricity : generate voltage in response toapplied stress

• Piezzoresistive : change in resistance in responseto applied stress

• Magnetostriction : change in shape asconsequence of applied magnetic field

• Magnetoresistance : change in electrical resistivity

in response to applied stress• Semiconductors : gap in the electric band

structure



Patterns and waves : crystals

1 nm 1 nm wavelength

electronic waves



Photonic crystals

1 micrometer Infrared light



Granular materials

• Sand• Portland cement

• Plaster

Macroscopic particles characterized by a loss of energywhenever the particles interact (mostly friction)

• Brazil nut effect (big on top)

• Salt cellar effect (clog)• Compacted granular material must expand (or dilate) before it can deform• No turbulence is almost impossible to achieve in granular materials• Granular materials can support (small) shear stresses indefinitely• Granular materials are often inhomogeneous and anisotropic• Granular materials exhibit avalanches



Cements

• Hydraulic cements (Portland cement)

Harden after combining with water, as a

result of chemical reaction with the mixing

water and, after hardening, retain strengthand stability even under water.

• Non Hydraulic cements set by reaction

with atmospheric carbon dioxide.



Building with cement

• Dry sand : no cohesion

• Wet sand : cohesion bycapillary forces

• In concrete : dissolutionreaction generatingcalcium silicate andaluminate ions : calciumsilicate hydrate (C-S-H)



Plaster (gypsum)

• When the dry plaster powder is mixed with

water, it re-forms into gypsum, initially as

a paste but eventually hardening into a

solid. The structure consists of sheets of Ca²+ and SO4²- ions held together by

hydrogen bonds in the water molecules.

The grip between these sheets is easilybroken, so plaster is fairly soft.



Material science



Mechanic characterization

Thermo characterization (melting point)

Optical and electromagnetic characterization

(refractive index)NMR (and other resonances)

Spectroscopy

Electrical characterization

Characterization



Material characterization

Idea :

– Probe a material

– And measure its response

• Probe : mechanically, electro-magnetically,temperature, waves, particles, vary directions,vary frequencies …

EXTREMELY COMPLEXI’ll give here some very simple examples



Instron :mechanical testing

Impose : constant speed

Measures :Force necessary to apply theconstant speed ( precision 0.1N)

Measures positions (precision :0.01 mm)

E th k



Extension (mm)

Earth quake



What do you measure ?

• Stress strain and surface :



How to measure Poisson’s ratio

• Poisson's Ratio :

1 - 2(VT ÷ VL)2 ÷ 2 - 2(VT ÷ VL)2

VT = Shear (transverse) Velocity

VL = Longitudinal Velocity

You need to measure sound speed in 2directions simultaneously …

M lti i t



Melting point

Kofler bench (for powders ! ):



Refractive index

r r

ii

µ ε η

η η

=

=

2211

sinsin



Spectroscopy

• Study of matter and its properties by investigatinglight, sound, or particles that are emitted,absorbed or scattered by the matter under investigation.

• Example of probes : – IR light – Visible light – Magnetic Field

– Inelastic scattering of light to analyse vibrational androtational modes of molecules (Raman)

– Neutrons



Visible absorption spectra



Example of IR spectrum



Case study : Resistance measuring

Input impedance !



Experimental work

• Build a model to have estimates• Everything is an approximation

• Nothing is really linear, it’s linear by

domain• Contacts/joints/interfaces : always a

problem

• Everything varies with frequency !

• Everything depends of the time scale youare using.

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Material Charecterization