material charecterization
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Materials characterization andtesting
HTMSTM(A)A class 2007George PopescuProf. Neil Gershenfeld
MIT Media Lab
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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
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Material science
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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
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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.
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Plasma…
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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 ?
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Phases
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Supercritical CO2
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You thought you knew ice ?
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Si/Au alloy look like this :
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Eutectics
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Lead/tin
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Defects in Crystals
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Strength vs defect density
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Heat Treatment
Tradeoff between ductility and brittleness
• Annealing,
• Case hardening
• Precipitation strengthening,
• Tempering• Quenching
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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.
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For this class : solids
Hooke's law :
Poisson's ratio :
F= -kx
Elasticity
ViscoelasticityPlasticityThermoelasticity
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Isotropy / anisotropy : birefringence
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Deformations
stress
Normal to
surface
Tangential
to surface
compression
tension
Young modulus
strain
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Elastic/plastic : instantaneous
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Viscoelastic : viscous deformation
Purely elastic Viscoelastic
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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
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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
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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
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Tunable materials
• Polymers
• Meta Materials
• Digital Materials
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Polymers
organic/inorganic
Homopolymer/copolymer
Linear/branched
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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.
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Hydrogels
Capillary forces osmotic forces
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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).
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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
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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.
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Digital Materials
Digital
Tuneable
Active
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Error reduction
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Error detection
S Final 5ns 2 n s
Measured sizeExpectedsize
Standard deviation
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Error tolerance
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Tuneability
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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
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Patterns and waves : crystals
1 nm 1 nm wavelength
electronic waves
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Photonic crystals
1 micrometer Infrared light
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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
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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.
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Building with cement
• Dry sand : no cohesion
• Wet sand : cohesion bycapillary forces
• In concrete : dissolutionreaction generatingcalcium silicate andaluminate ions : calciumsilicate hydrate (C-S-H)
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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.
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Material science
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Mechanic characterization
Thermo characterization (melting point)
Optical and electromagnetic characterization
(refractive index)NMR (and other resonances)
Spectroscopy
Electrical characterization
Characterization
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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
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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
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Extension (mm)
Earth quake
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What do you measure ?
• Stress strain and surface :
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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
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Melting point
Kofler bench (for powders ! ):
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Refractive index
r r
ii
µ ε η
η η
=
=
2211
sinsin
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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
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Visible absorption spectra
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Example of IR spectrum
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Case study : Resistance measuring
Input impedance !
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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.