MSE 2001 - test 1

  • Explosion of materials around 1920

  • Currently in the silicon age - silicon is also a ceramic

    • Age of Materials today, this leads to better material selection and makes the possibilities much more broad

    • Also includes challenges such as having difficulty narrowing down options to choose the best material for different applications. Processing of many new materials is also complex

  • Materials science and engineering studies the inter-relationships between: Processing, Properties, and Structure

  • Engineers Design while scientists discover

  • MSE provides the “materials parameters” (material constraints) that are useful for other engineers to design.

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  • Mechanical/Structural Properties include:

    • Density

    • Elastic Modulus (Stiffness)

    • Yield Strength

    • Modulus of Resilience

    • Fracture Toughness

    • Hardness

    • Ductility

    • Poisson’s Ratio

    • Coefficient of Friction

  • Thermal Properties:

    • Heat Capacity

    • Thermal Conductivity

    • Melting Temperature

  • Chemical

    • Diffusivity

    • Corrosion Resistance

    • Solubility

    • UV protection rating

    • Biocompatibility

  • Price

    • cost of raw material

    • cost of processing

  • Electrical/Magnetic

    • Electrical conductivity

    • Magnetic Susceptibility

    • Magnetization
      Magnetic Remanence

    • Dielectric Constant

    • Polarization

    • Superconductivity

  • Optical

    • Refractive index

    • absorption coefficient

    • reflectivity

    • fluorescence/ emission

  • Cross-Properties

    • Thermal expansion

    • curie temperature

    • electro-optic coefficient

    • piezoelectric coefficient

    • thermoelectric

    • pyroelectric

    • emissivity

    • electrochemical properties

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  • Material Property / Material Constant: intrinsic property of material NOT dependent of size or shape

    • characteristics ending in “ity” are most commonly materials properties, NOT performance parameter

  • Performance parameter: Property of component the IS dependent on shape, size, and material identity

  • R=P(L/A) — R is the resistance (the performance parameter), P is the resistivity (the material constant) and L/A is the cross section area (or length/area)

    • Material properties can ALMOST ALWAYS designed around by making it a different size or shape, aka, if you want to achieve something with a certain material you can probably just change its size and shape, but its inconvenient b/c tradeoffs with other properties.

    • Why should you choose a different material?

      • original material may be too expensive, heavy, be impossible to process, etc.

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  • 1.2 - PRICE OF MATERIALS


  • importance of price: determines of product is commercially viable


  • Material driven costs:

    • Terrestrial abundance - (good first-order estimate for determining material cost

    • extraction costs

*rare earth metals are rare b/c they are not found in concentrated ores = expensive extraction cost


  • People-driven costs:

    • supply/demand

    • tech drives

    • speculation

    • geo politics

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1.2 - MECHANICAL AND STRUCTURAL PROPERTIES


  • Stiffness: Amount of force (stress) needed to flex the material [NOT PERMANENTLY DAMAGED]

  • Strength: Amount of force (stress) needed to deform the material [ PERMANENTLY DAMAGED but NOT BROKEN]

  • Toughness: Amount of force (stress) needed to break the material [BROKEN]


Measuring Mech Properties:

  • Performance parameters

    • Load: Force (N, lb, kg)

    • Total elongation: ∆L (cm, mm, in)

  • Material Properties

    • Stress Θ : Load/ cross - section area = N/m² = Pa (MPa, GPa)

    • Strain ε : ∆L/L0 = Lf - L0 / L0 = mm/mm = UNITLESS


  • Tensile tests: provides data for the stress-strain curve

  • Elastic/linear section: deformation occurs that is reversible - material returns to original shape and has 0 strain when load is removed

  • Elastic Modulus (stiffness E) : slope of elastic portion

    • definition: material’s resistance to stretching, bending, and flexing

    • inc Elastic modulus = inc stiffness = inc E = inc resistance to stretching, bending, and flexing

    • Hooke’s Law: Θ = Eε = E = Θ/ε = slope

  • Poisson’s Ratio (v): a measure of how much a material will shrink or expand sideways when stretched/compressed lengthwise

    • ν=(-ε_trans)/ε_axial

      • “Perfect isotropic materials: 0.25

      • Most materials: 0.3

      • Unusual cases: cork = 0.0, auxetic = - (negative value)


  • Plastic/non-linear section: deformation occurs that is irreversible/permanent - material does NOT return to original shape when load is removed

  • Yield Stress, σy, strength: stress required to permanently deform material

    • located on y axis where elastic and plastic sections meet

  • Ultimate Tensile Strength σUTS: ultimate strength. stress beyond is when material fails/fractures

    • located at highest point of plastic section

  • Ductility εf: maximum amount of strain (% elongation) at failure

    • located on x axis, parallel to end of curve on graph


  • Modulus of Resilience

    • Resilience is a materials property describing the amount of elastic energy per volume that is reversibly absorbed

      • found w/ integral of elastic region

  • Coefficient of restitution is a corresponding performance parameter

    • (round vs cube bouncy ball) SHAPE MATTERS

  • Toughness measures energy per volume required to BREAK a material

    • found on stress strain curve as the area under the curve


  • Hardness: surface property

    • describes how difficult it is to scratch a material

    • measured using the Moh’s scale, based on semi quantitatively (not even steps)

    • Brinell hardness measures hardness more evenly

    • chemical vapor deposited oxide coating (a ceramic) allows for safety goggles to not be scratched as much


Sound Waves

  • Sound transmitted through materials in longitudinal strain waves (or aka mechanical waves)

    • velocity prop to sqrt of (eleastic modulus / density)

  • Acoustic Impedance: sound travels from a material to a different one, different impedance of sound determines how much is reflected or transmitted.

    • Z prop to sqrt(density * elastic modulus)

    • LARGE Z mismatch = mostly reflection of sound

    • SMALL Z mismatch = mostly transmission of sound


Thermal Properties

  • Maximum Service Temperature: max “useable” temp of a material, above it will fail

    • service temperatures are often much much lower than the materials melting point (50 - 80%)

  • Heat Capacity: materials constant

    • energy required to raise temp of material by 1 degree C

    • aka amount of heat energy stored per amount of material

    • can by J/m³K or J/kg K or J/mole K

  • Thermal Conductivity (lambda): speed of heat flow

    • rate of which heat flows through a material at steady state (temp gradient constant with time

    • follows Fourier’s law: Q = -lambda ∆T/∆x == heat flux = conductivity ( change in temp/m)

  • Thermal Diffusivity: material property describing transient heat flow (m²/s)

    • estimates how quickly a material will heat up and reach a certain temp as a source is applied to it

      • D_th = lambda/Cp = diffusivity = thermal conductivity / heat capacity

    • Inc of thermal conductivity = faster melting

    • Inc heat capacity = more heat released

  • Thermal expansion Coefficient(alpha)

    • CTE: change in volume of a material with change in temp (expand when heating)

    • both mechanical and thermal property

    • ∆L = aLi∆T = E = a∆T === mech strain = CTE * temp change

    • common issue buckling: choose material with low CTE to avoid it

    • Bimetallic strips: 2 materials with different CTE’s

      • De-lamination: film on ceramic substrate → glass expands but can’t bend, therefore film flakes

    • as long as the yield stress’s of the materials to not exceed, the bending is reversible and repeatable for calibration → ex: thermometers

    • when choosing CTE of 2 materials, chose the closest 2 CTE’s

    • the higher CTE experiences compression at high temps


  • materials thermalize best w/ HIGH thermal conductivity and low heat capacity


Electronic Properties

  • Electrical Conductivity (theta): how quickly electrons/electricity travel through the material (units: S/cm siemens/cm)

  • Electrical Resistivity (p): material property

    • OPPOSITE of conductivity, the impediment to electron flow (units: omega * cm)

    • Relationship: S=1/omega


    • (conductors, semi conductors, insulators) → increasing resistivity and decreasing conductivity

  • Electrical Resistance (R): preformance parameter

    • R = P(L/A) == resistance = resistivity (length/area)

  • Electrode = electrical conductor

  • Dielectric = electrical insulator

  • Capacitor = stores a charge

    1. charging ( a battery placed)

    2. stores charge (charge in the electrode/dielectric)

    3. Discharge (send charge to item - ex light bulb)

    • Equation for capacitance: C=Eo k (A/t) == vaccum permitivity dielectric constant (area/thickness)

    • important material properties of capacitor’s dielectric material

      • k - dielectric constant - amount of charge you can store

      • p - resistivity - how long(avoid self discharge)

    • capacitor stores ELECTRICAL energy while battery stores CHEMICAL energy

      • capacitor is faster

  • Piezoelectricity: cross-property of electrical and mechanical

    • electrical insulators bc mush support internal applied voltage to function

    • Basically: apply mechanical strain to get a voltage is piezoelectricity and applying a voltage to get a mech strain is electrostriction within piezoelectric materials

    • most common material of piezoelectricity is lead zirconate titanate (PZT)

      • quartz is also piezoelectric

  • Semiconducting Materials

    • semiconducting materials can behave either as insulators OR conductors but neutrally they are insulators (aka off)

      • become conductive (aka on) w/ energy is applied

    • Very useful w/ SWITCH applications

    • have moderate band gap so changes in energy can make semiconductors either a conductor or insulator

    • Altering semiconductor properties

      • Doping: intential defects/impurities added to pure semi-conductors

        • dopants decrease ∆E (band gap energy)

    • Transistors: use semiconducting materials to act as switches

      • In enhancement mode MOSFET, a voltage is applied that is above the threshold band energy gap that is applied to the gate, ultimately switching the semiconductor to on and conducting

      • With no signal or not enough signal applied to the gate, the switch is off and not conducting


Magnetic Properties

  • Magnetization

    • material’s response to an applied magnetic field

    • M=xH == Magnetization = susceptibility * external magnetic field (M and H are vectors)

    • Magnetic susceptibility (x): materials property

  • “Magnetic” Materials:

    • Ferromagnets

    • Ferrimagnets

  • “Non-Magnetic” Materials:

    • Paramagnet

    • Diamagnets

    • Antiferromagnets

  • Superconductors:

    • ALL superconductors are diamagnets but not all diamagnets are superconductors

    • All true superconductors exhibit Meissner-effect, which is temp dependent

      • Below transition temp, electrical resistivity drops sharply and magnetic fields are repelled from material

  • Behavior of Magnetic Materials

    • Soft magnetic materials → when apply a magnetic force they magnetize → when magnetic force removed the material demagnetizes

    • Hard magnetic materials → when apply a magnetic force they magnetize → when magnetic force removed the material STAYS magnetized

  • MH loops - Hysteresis Curves

  • Ms: Saturation Magnetization:

    • max magnetization as loop goes horizontal

  • Mr: Remanent magnetization:

    • how much magnetization “remains” at zero H

    • y-intercepts

  • Mc: Coercive Field:

    • how easily switch direction of magnetic field in a material

    • x-intercepts

    • (H value where M switches direction)

  • Curie Temperature:

    • temp above which a permanently magnetized materal (hard magnet) looses its magnetization

    • aka the service temp for magnetic materials

    • curie temp is temp at x-intercept



Optical Properties

  • When light is incident on material there are 3 results:

    • reflection, absorption, and transmission

    • Io = Ir + Ia + It == 1 = R + A + T = 100%

  • color of material:

    • reflectivity, absorptivity, and transmissivity all depend on wavelength of incident light and angle of incidence

    • color of material is the wavelengths that are NOT absorbed

      • seen by reflection in opaque materials

      • seen by transmission in transparent materials

    • UV/Vis Spectroscopy is technique to measure amount of light absorbed by material

      • materials that reflect most wavelengths appear white

  • Gold Nanoparticles & Ruby Glass

  • ___________

  • Reflectivity depends on the Angle of Incidence

    • A glancing/glazing incident with a small incident angle results in mostly reflection

    • A near normal incident results in mostly transmission

    • A “smooth” reflection: specular reflection from a smooth surface and is mirror like

    • A “blurry” reflection: diffuse reflection from a rough surface due to more scattered light

  • Polarization of Light

    • light is an electric field and a magnetic field oscillating perpendicular to each other

    • the polarization direction of light wave is direction of electric field is oscillating

      direction of light wave is axis perpendicular to polarization direction

    • Most light sources have randomly polarized light (waves w/ electric fields in all directions)

      • light can be linearly polarized by passing through a polarizer (a material w/ only direction of linearly transmitted polarized light

      • in randomly polarized light, half of light intensity is found in the 2 vector components

        • therefore, when linear polarized the 1st time the intensity is cut by 50% and the 2nd time polarized perpendicularly, all light is blocked


        • Polarization of Light

    • Cross-Polarizers: vertical + horizontal orientations = blocks all light

    • Light Sources: Randomly polarized: 1 filter block 50% and crossed filter block all

    • Light reflections: preferential polarization → polarizers in the right direction cut glare down


  • Refractive Index(n): material property

    • ration of velocity of light in vacuum to velocity of tight traveling in material

    • larger n = light is slower

    • Air, n = 1 → no slowing

    • performance parameter of interest is ANGLE OF REFRACTION: n1sin(0) = n2sin(02)

      • as light enters a slower material, it bends toward a surface normal (angel gets smaller)

    • ….

  • Optical dispersion: material property

    • describes how much the refractive index of a material varies with the wavelength of incident light


1.5: chem properties

  • Diffusivity: material property

    • determining how fast atoms diffuse through a material

    • xavg = sqrt(Dt)

    • What effects diffusivity?

      • temp - higher temp = increase of diffusivity exponentially

      • type of bonds - stronger bonds = higher Ea = slower diffusion

      • amount of “open space” between atoms - more space = less resistance = lower Ea = faster diffusion

        • why polymers diffuse fast

  • Atomic diffusion in solid state:

    • Thermally activated atomic process - Arrhenius behavior/process:

      • begins at rest state, increase in energy needed to squeeze other atoms out of position (transition state) back to rest state

      • Arrhenius equation: D=Dexp[-Ea/kbT]. ratio of energy requirment to energy available

      • HIGHER EA = SLOWER DIFFUSION

      • HIGHER KbT = FASTER DIFFUSION

  • Durability:

    • the material and environment determine dominant degradation mechanism

    • common mechanisms:

      • solubility

      • oxidation

      • corrosion

      • photodegradation - UV light breaks bonds

  • Stable State of Elements

    • Most elements are most stable when formed with oxides, resulting is most materials oxidizing at some rate, which is accelerated within high temperatures

  • Oxidation:

    • chemical reaction between a metal and oxygen gas

      • M+O2 = MOx

    • if the structure of metal does not equal the structure of MOx, than creaks result in the oxide and lead to fresh metal oxidizing and continued damage

    • Protective Oxide Layers:

      • self-terminating oxides form protective coating at a few nanometers thick

      • protect from further oxidation and can re-form if scratched off

        • ex. Al → Al2O3, Si→ SiO2, etc.

      • These elements are mixed with other ones more susceptible to oxidation for protection

    • Anodization (controlled Oxidation):

      • through application of a current to the material in an aqueous bath results in a thicker more protective oxide coating

      • Advantages include:

        • reduction of harmful oxidation - physical barrier from O2 diffusion

        • oxide coating has a high hardness → scratch resistence

        • coloring of material - through dye or voltage

    • Corrosion (destructive Oxidation):

      • an electrochemical (redox) reaction, typically with a metal in an aqueous environment

      • Standard Reduction Potentials (given 3 elements):

        • what is going to be oxidized? → whatever is lowest on chart.

        • what is going to be reduced? → next lowest on chart

        • what is bystander/least reactive → lowest

      • Galvanic Corrosion:

        • process when 2 diff metals in electrical contact in water → create galvanic cell

        • two redox reaction:

          • oxidation(corrosion) - at the anode [OIL → oxidation is loss)

          • reduction - at the cathode [RIG → reduction is gain]

          • rate of corrosion increases with Temp, salt concentration, and PH

          • elements with smaller standard reduction potentials are more likely to be oxidized - act as anode

          • elements with larger standard reduction potentials are more likely to be reduced - act as cathode

            • NOT CORRODED - ONLY REDUCED

        • PREVENTING galvanic Corrosion

          • eleminate electrical contact, reduce exposure of metal-metal interface, use CATHODIC PROTECTION: use sacrificial metal (not corroded) (pipe next to pipe ex.)

      • Galvanizing:

        • Used to apply to ferrous (iron-based) metal alloys - adds coating of sacraficial metal

        • most steel dipped in zinc, providing a physical barrier and cathodic protection


1.6 - classifying materials

  • Major Classes of Materials:

    • Metals - inorganic, metal alloys, inter-metallics

    • Ceramics - metal + nonMetal, glass, semiconductor

    • Polymers - non-metal elements, elastomers

    • Composites - 2+ material classes or hybrid

  • Polymer (Plastics):

    • “Organic solids” - has mostly carbon and hydrogen - may also contain O,N,S,Cl,F and sometimes Si

    • most identifiable through long carbon chains

    • solid polymer is entangled “mess of spaghetti” hydrocarbon chains that slide past each other (aka amorphous random arrangment)

    • most polymers have a amorphous microstructure, some semi-crystalline polymers have a few ordered regions

    • Mechanical Properties:

      • LOW elastic modulus (very stretch)

      • high toughness

      • may be brittle (depends)

    • Electrical:

      • commonly electrically insulating

    • Thermal:

      • low thermal conductivity

      • low service temperature

    • Optical:

      • often transparent/translucent

      • able to be dyed

    • Chemical:

      • Corrosion resistant

      • dissolve/swell in organic solvents

      • reacts with strong oxidizers and photodegradation

    • Others:

      • LOW density → strength per weight ration similar to metals!

      • easy process into various shapes

      • low stiffness

      • low service temp

    • Elastomers:

      • have extremely low elastic modulus and very high strain at yield


  • Ceramics

    • often composed of oxides and can be other “ides”

    • Gem stones and most other “rocks” are mostly ceramics

    • ceramic is referring to the crystalline version of these solids (crystalline = ordered atomic structure)

    • GLASS: sub class of ceramic w/ amorphous structure

    • Both crystalline and glass ceramics are brittle and corrosion resistant

      • differences include crystalline structures (like quartz) being harder, piezoelectric, and have higher melting point

      • Glass (such as fused silica) is softer, has a lower melting point, is NOT piezoelectric, and is more transparent

    • Mechanical properties:

      • stiff but brittle (no plastic deformation, low E at failure, fractures near yield point

    • Electrical : most ceramics are good insulators

    • Thermal:

      • mid thermal conductivity

      • EXCELLENT temp stability, stable above 1000C -2000C

        • glass has lower service temp and thermal conductivity

    • Optical

      • crystalline is opaque or translucent/transparent, glass is transparent

    • Chemical:

      • corrosion resistant

      • durable against acids/organic solvents

    • Other:

      • high hardness

      • can withstand mech loading in compression, but NOT tension (like bricks)

      • difficult to machine/shape bc high service temp, stiffness, and hardness

    • Semi-conductors: sub class of ceramics that are NOT oxides

      • similar properties except CAN BE conductors

      • Can be group 4 elements, 3-5 semiconductors, or 2-6 semiconductors


  • Metals & Metal Alloys

    • Inorganic solids formed of only metallic elements - can be composed of single element or a mix

    • almost always crystalline solids

    • Alloys

      • A mixture of 2+ elemental metals - crystalline but randomly arranged

      • Ex. Brass - Cu and Zn - no precise stoichiometry - Zn are randomly placed in Cu lattice

      • aka solid solution - solute = Zn and solvent = copper

    • Mechanical properties:

      • high elastic modulus (stiffness)

      • pure elemental metals have low yield strength (easy to deform)

      • alloying improves yield strength

      • good toughness

    • Electrical: good conductors

    • Thermal:

      • good thermal conductors

      • intermediate service temps of less than 1000C

        • exception tungsten which is 3500

    • Optical:

      • often opaque in diff ways

      • relective in UV and visible, absorb longer wavelengths

    • Chemical: susceptible to corrosion and chemical acid attacks

    • Other: EASY to machine/deform/shape

    • Intermetallics:

      • sub class with PERCISE stoichiometry

      • crystalline structure w/ repeating pattern - similar to ceramics

      • compared to other metals and alloys:

        • less tough, more brittle, higher melting point, higher hardness

        • Note: nitinol has shape-memory!

  • Composites

    • 2+ material classes merged to try and obtain both types of properties

    • Often more expensive than individual classes b/c of manufacturing and processing costs

    • Ex. Carbon Fiber: ceramic in polymer matrix

      • 2x stiffnes of steel

      • 10x stiffness to weight ratio

      • creation: take polymer and heat it to get pure C, add stabalizing chemicals, and a polymer matrix

    • Composite mixing laws:

      • try to optimize tradeoffs between properties

      • composites can either show worse or better properties than a simple linear interpolation

      • properties depend on surface/interface engineering and geometric arangement