mse 2001 unit one

opportunity of materials

better, more specific properties and broaden design space

challenge of materials

material selection (how to pick best materials)

components of material science and engineering (mse) paradigm

composition and structure, properties, processing

composition

chemical makeup of material

structure

spatial arrangement of atoms in a material

processing

steps to convert raw materials into its final form

properties

behavior of a material under particular conditions or environment

study of mse

interrelationship between composition and structure, properties, and processing to understand their effects on material performance in particular application or environment

what engineers do

design

what scientists do

discover

what does mse provide

material constants that other engineers use for design

material constant/property

inherent property of a material that does not depend on size or shape

examples of material constant/property

resistivity, elasticity, thermal conductivity

performance parameter

property determined by size, shape, material, identity

stiffness

how much force (stress) does it take to flex the material; not permanently deform

strength

how much force (stress) does it take to permanently deform (not broken) the material

toughness

how much energy it requires to break the material

performance parameter

property that is affected by size and shape (Ex. load, total elongation)

material properties

dimension independent of size and shape, normalized by initial sample size (Ex. stress and strain)

stress (σ)

intensity of distribution: force/area (units of Pa)

strain(ε)

ratio of deformation (change in length/instantaneous length)

tensile testing

data on mechanical properties in the form of the stress strain curve

ultimate tensil strength

max stress an object can withstand; deformation becomes concentrated afterwards and material fails/fractures after

elastic deformation

reversible deformation, linear (if remove load -> material return to original load); bonds behave like springs

young's modulus (elastic modulus)

stiffness of the material; material's resistance to stretching, bending, flexing (σ=Eε)

shear modulus (G)

measures a material's stiffness and resistance to deformation when subjected to shear stress (forces acting parallel to opposite surfaces)

flexural modulus (Ef)

measures a material's stiffness or resistance to bending, determined by the ratio of stress to strain in flexural deformation.

poisson's ratio

the negative of the ratio of the transverse (lateral) strain to the axial (longitudinal) strain in axial tensile loading; usually 0.3 (perfect isotropic material is 0.5)

plastic deformation

material does not return to original size/shape when load is removed ;nonzero strain at zero stress once plastically deforms, stress is not proportional to strain

yield stress (σy)

strength; stress required to permanently deform the material

ductility (εf)

maximum amount of strain (%elongation at failure) - strain at break

resilience

amount of energy return to material in collision on per volume basis; material property (area under elastic portion of curve); coefficient of restitution

toughness (graph)

energy per volume required to break a material; area under total curve (J/m^3)

hardness

surface property of a material (how difficulty to scratch); moh's hardness scale and vicker's hardness test

sound

transmitted through materials as longitudinal strain waves (v ~ sqrt(E/p))

acoustic impedance (Z)

the resistance to sound traveling through a medium (Z ~sqrt(pE))

large Z (acoustic impedance) mismatch

energy reflection

small Z (acoustic impedance) mismatch

energy transmission (air and foam minimizes sound reflection and mismatch)

large Z (acoustic impedance)

higher density and stiffness (ex. steel, copper, glass)

small Z (acoustic impedance)

small density and stiffness (ex. water, plastic, foam, rubber)

sound absorption coefficient

the larger it is, the more it prevents sound from traveling further (ex. polymer and foams: 0.01 to 0.2 and metals/ceramics: 10E-6 to 10E-4)

service temperature

temperature at which the device can withstand without incurring a change in its physical properties; much lower than melting point (0.5 - 0.8Tm)

specific heat capacity

amount of heat energy required to raise the temperature of a material (per unit mass/mole/volume) by 1C; materials constant

heat energy quantized

as phonons which move through solids causing thermal conduction

does heat flow in a preferred direction

follows temperature gradient

thermal conductivity

speed of heat flow/how much heat passes through across a temperature gradient at steady state

steady state

temperature gradient is constant over time

fourier's law

(aka law of heat conduction) the transfer of heat moves through matter from higher temperatures to lower temperatures in order to equalize differences

thermal diffusivity (Dth)

how fast material changes temperature in temporary state

thermal expansion coefficient

change in dimension of material with change in temperature (thermal + mechanical); high causes buckling)

cte mismatch

causes rippling, buckling; bending can be reversible

bimetallic strips

higher a--> expansion for temperature sensitive mechanical switches; largest deflection with highest mismatch or temperature difference

electrical conductivity

ease with which material can conduct electric current (how fast electrons move through material)

resistivity

how strong resistance to electron flow/migration' material property

resistance

material's opposition to the flow of electric current; performance parameter (inverse of conductivity)

dielectric

electric insulator

capacitor

stores and releases energy; made of electrodes with dielectric between

battery

stores electrochemical energy

piezoelectricity

electric insulators because must support internal applied voltage to function (electrical and mechanical response)

piezoelectric coefficient (d33)

~300 pm/V; small effect indicates very precise

band gap theory

band structure of material tells how many electrons can move (metals overlap and have no band gap, increases with semiconductors and insulators); band between conduction and valence

semiconductor

act as insulators or conductors; behave as insulators at neutral state and become conductive when overcome the energy gap; switches

doping

add defect/impurities on purpose to change electronic behavior

magnetization (M)

material's response to applied magnetic field (H), measurable where M = xH

magnetic susceptibility (x)

how easily influenced, material property

hysteresis curve

m-h curve, lag between field (H) and material response (M)

coercitivity (Hc)

reverse force to break domain and bring total magnetization to zero

remanence (Mr)

leftover magnetism when H is removed

saturation magenitization

largest value of M

hard magent

holds magnetism well with high remanence and coercivity

soft magent

does not hold magnetism well with low remanence and coercivity

non-magentic

paramagnet, diamagnet (resist dipole) , antiferromagent (alt aligned)

magentic

ferromagnet (aligned in zero field), ferrimagent (somewhat aligned in zero field)

meissner effect

below critical temperature, electrical resistivity drops and magnetic fields are repelled; property of true superconductor

oxygen

paramagentic, attracted to external magnetic field

nitrogen

diamagnetic, not attracted to external magnetic field

curie temperature

above curie temperature, permanent magnets lose their magnetization (permanent unless re-magnetized by strong external magnetic field); service temperature for magnetic materials

light

electromagentic radiation, thought as wave/photon

equation for reflection, absorption, transmission (rat)

Io = Ir + Ia + It (or 1 = R + A + T)

opaque

no light passes through (T=0; ex. wood, metal, stone)

transparent

little scattering, can see clear images through it so T ~1 (ex. glass, clear water)

transluscent

light passes through, internal scattering; 0<T<1 (ex. wax paper, frosted glass)

wavelength color

depends on what wavelength reflected or transmitted (NOT ABSORBED)

uv-vis

technique to measure optical properties (rat) of material as function of wavelength

quantum dots

tunable color, can alter visible color by later size of nanoparticle; relationship between particle size and optical absorption (quantum confinement)

smooth reflcetion

specular; from smooth surface

blurry reflection

diffuse; from rough surface

refractive index

a measure of the light-bending ability of a medium; materials property (larger n --> slower velocity of light--> more bent --> image shifted more)

snell's law

angle of refraction: n1sin(theta)1 = n2sin(theta)2

diffusion

random motion of atoms in a system

diffusivity (D)

material property that determines how fast atoms diffuse through a material (exponentially increased by increase in temperature)

fick's first law

The diffusion flux is proportional to the concentration gradient. This relationship is used for steady-state diffusion situations.

fick's second law

The time rate of change of concentration is proportional to the second derivative of concentration. This relationship is used in nonsteady-state diffusion situations.

mechanisms of degradation

solubility, oxidation, corrosion, photodegradation

common methods to improve durability

coating (thermal, environmental), additives (flame retardants, uv absorbers), cathodic protection, pick different material

oxides

most stable state for most elements

oxidation

chemical reaction between metal and oxygen gas (expansion --> cracks cause increase in oxidation)

anodization

oxidation process in which a film is produced on the surface of a metal by electrolytic treatment at the anode; control surface color

galvanic corrosion

two different metals in electrical contact in presence of liquid water environment (lower standard reduction potential is easier to oxidize); prevent via rid electrical contact, reduce exposure

galvanizing

use cathodic protection with coating of sacrificial metal (usually zinc)