Point:

Vacancy

Interstitial

Substitutional

Linear:

Edge Dislocation

Screw Dislocation

Planar:

Surface

Grain Boundary

Volume:

Void

Non-crystalline region

1) Vacancy Assisted

2) Cyclic Exchange

3) Simple Exchange

4) Simple interstitial

5) Interstitial by displacement

High Temps

Small atoms/ions

Lower packing factor

higher free volume

Dislocation movement causing micromechanical deformation

Occurs in planes with high atomic density (close packed planes) in directions of high atomic density.

close-packed planes and close-packed directions.

ie: FCC: {111} Planes and <110> Directions, has three slip directions and 12 members in the slip system.

BCC: {110} planes and <111> Directions, 12 members in the slip system.

The more members in the slip system the easier it is for plastic deformation to occur.

The load neccessary to produce a given elongation in monitered as the specimen is pulled in tension at a constant rate. 

results in a load v. elongation curve (stress/strain)

Load on the sample / cross section of the sample

σ = P/A_o

Gage length at given load / original gage length

ε = Δl / l_o

permanent deformation

only a small elastic component is recovered when load is removed.

Represented as the intersection of the deformation curve with a straight line parallel to the elastic portion and offset .2% on the strain axis.

Represents the stress necessary to generate .2% of permanent deformation.

E

slope of the stress-strain curve in the elastic region.

linearity of the stress-strain plot in the elastic region

σ = Eε

(NOTE: E represents stiffness: resistance to elastic strain)

Strength per unit density

gives you an idea of the strength to weight ratio, which is important for design considerations.

T.S.

Stresses above the yield, reach a maximum at T.S.

the region between is referred to as strain hardening.

The general ability of the material to be plastically deformed.

G = shear stress / shear strain

E = 2G (1 + poissons's ratio)

...Strength parameter for ceramics and glasses

MoR = 3FL / 2bh²

measured by bending test

assumed that in any real material there would be numerous ellipticall cracks at the surface and/or in the interior.

The highest stress exists at the tip of the crack

σm = 2σ(c/p)^1/2

Flexural Strength / Modulus

FS

Equivalent to MOR for ceramics

describes the combined effects of compressive deformation and tensile deformation

E_flex = L³m / 4bh³

m = slope of tangent line

Deliberate deformation of a metal at relatively low temps.

metal becomes more difficult to deform

a dislocation hinders the motion of another

restricting plastic deformation by forming solid solutions.

causes the elastic region to be extended

Stress relieving heat treatment

produces more perfectly crystalline structures.

dislocation density decreases

cold working

annealing

solution hardening

actual shear stress operating on the slip system (in the slip plane and slip direction) resulting from the applicaiton of a simple tensile stress.

Slip direction - Fcosλ

Τ = Fcosλ / (A/cosφ) = σcosλcosφ

Resistance of the material to indentation. 

indicates strength.

test conducted with rounded or pointed indentor and loaded on specimen surface.

fairly linear correlation with strength

tensile strength is generally used over YS bc the hardness test includes plastic deformation.

microhardness

uses a large area diamond pyramid.

Plastic deformation occurring at high temps (1/3 to 1/2 Tmelting) under constant load for long times.

1) Primary - decreasing strain rate, increases slip with temp causing increasing dislocations

2) Secondary - constant strain rate. increased ease of slip is balanced by and increased resistance due to the number of existing dislocations

3)tertiary - strain rate increases due to increase in true stress due to a decrease in area due to necking or internal cracking.

Given by Arrhenios Expression

e = Ce^-Q/RT

material does not just simply "snap back" to its original conditions after stress removal.

Relaxation time T

1/T = Ce^-Q/RT

Charpy Test

measures impact energy. directly calculated from the difference in initial and final heights of the swinging pendulum.

A stress concentrating notch is cut into the sude subjected to max tensile stress.

A large YS, TS and Ductility increases fracture energy.

Izod Test

Impact energy for polymers.

Represented by K_{IC -} critical value of stress intensity factor at a crack tip necessary to produce failure under simple uniaxial loading (mode I)

 K_{IC =} Yσ_f(pi a)^1/2 [Mpa/m^1/2]

Y - dimensionless geometry factor

material failure after several cycles of loading to a stress less than ultimate tensile stress.

rate of crack growth da/dN = A(ΔK)^m

Stress intensity factor ΔK = K_max - K_min = YΔσ(pi a)^1/2

Characteristic of ferrous alloys (slow decay in strength with increased N, cycles)

nonferrous alloys - rate of decay decreases with N

common in glass and ceramics.

1) occurs in water containing enviroments

2) occurs around room temp

Chemically and structurally homogenous portion of the microstructure.

Distinct chemical substances from which a phase is formed

compounds can be considered single components

Number of independent variables avaliable to the system

metal at melting point has 0 dof

Temp, Pressure and Compostion

all affect the microstructure and dof

Relates the dof and the state variables

do(F) = C - P + 2

if P = 1 atm then: F = C - P + 1

C- # of components, P- # of phases

greater dof can mean that you could maintain the same microstructure with a change in temp... composition becomes a dependent variable.

a mixture of chemical compounds or elements that has a single chemical composition that solidifies at a lower temperature than any other composition.

 the temperature is known as the eutectic temperature.

On a phase diagram the intersection of the eutectic temperature and the eutectic composition gives the eutectic point.

Eutectoid

When the solution above the transformation point is solid, rather than liquid, an analogous eutectoid transformation can occur.

For instance, in the iron-carbon system, the austenite phase can undergo a eutectoid transformation to produce ferrite and cementite, often in lamellar structures such as pearlite and bainite.

I If the alloys' composition places it to the left of the eutectic point on a phase diagram, then it is hypoeutectic.

Note, though, that the phase diagram must have a eutectic point to have hypoeutectic or hypereutectic alloys.

Used to determine the amount of each phase in the two-phase region

Note: in a single phase region it's 100% of that single phase.

Mass Balance: requires that the sum of the two phases equals the total system.

"many mers"

1) resistant to chemical attack

2) good thermal/electrical isolators

3) lightweight for a given strength/toughness

4) can be processed into finer/intricate forms

rigidity and melting point increase with complexity of the molecular structure.

pheno-formaldehyde - rigid, even brittle

linear polyethylene - relatively soft

Linear structure has covalent bonds all along the backbone. weak, van der waals, bonds hold together adjacent bonds. causing the molecules to be relatively free to slide past each other... leading to low elastic modulus.

1839 - Charles Goodyear - Rubber

1860's - Alexander Parkes - Nitrate celulous

- Wesley Hyatt - Celluloid

1880's Comte de chardonnay - flammable

1890's - cross, bevan and beadle - artsilk (rayon)

1900's - Leo Hendrick Bakeland - Bakelite

Polymerization

2 ways

Process by which long-chain of network molecules are made

1) chain growth - involves rapid chain reaction of chemically activated monomers

2) step growth - involves individual chemical reactions between pairs of reactive monomers.

presence of reactive sites:

Double bonds in chain growth

Reactive functional groups in step growth

recombination

hydrogen abstraction - obtaining a hydrogen atom (w/ unpaired electron) from an impurity hydrocarbon group

disproportionation - formation of a monomer like double bond.

-Plastic behavior at high temps. Elastic at low.

-Become soft and deformable upon heating. characteristic of linear polymers molecules.

-High-temp plasticity due to molecules ablility to slide past one another (creep deformation)

-Ductility decreases upon cooling

-Secondary bonds must be broken for this to occur.

polymers with sufficient strength and stiffness for structural applicaitons

ex: nylon and polyethylene (most common)

elastomer - polymer with mechanical behavior analogous to natural runner

advantage: connivence of processing by traditional thermoplastic techniques.

become hard and rigid upon heating, which is not lost upon cooling.

materials share signifigant strength and stiffness.

Disadvantage: non recyclable and less-variable processing techniques.

Additives

used to provide specific characteristics to the polymers

Plasticizer - softens polymer

Filler - strengthens polymer. low cost.

Reinforcements - enhanced strength and stiffness

Stabilizers - reduce polymer degredation

Flame retardants

colorants/pigments/dyes

involve some combination of two or more compnents from the fundamental structural material types:

metals, ceramics/glasses, polymers

Point being, to get the "best of both worlds"... best property of each material.

Fiber: ie Fiberglass (super common)

continuous, woven or chopped

Particulate

aggregates...

reinforcing fibers have moduli higher than E-glass

generally involves carbon and kevlar

increased strength and temp resistance

decreased weight

developed for temp, conductivity and load conditions

ie boron-reinforced Al and Carbon-reinforced Al

Alumina-reinforced Al

high modulus and high strength

increased cost due to process of forming the large carbon chain molecules.

particulate composites - systems in which the dispersed particles are relatively large and present in high concentrations. (>25% vol)

ie cement

Dispersion-Strengthened: small concentrations of oxide molecules (<15% vol). oxide strengthens metals by serving as obstacles to dislocation motion. increases tensile strength. 

increased fracture toughness for ceramic-matrix composites.

better specific strength: strength to weight ratio

NOTE: there is a substantial cost associated with most "advanced" composites. this cannot be justified by the strength alone, but because of the strength for a given weight. 

iron-based - carbon, alloy steels, cast irons

nonferrous alloys - all other metals that don't contain iron as the major constituent.

Steel - .05 - 2.0 wt% C

Cast Irons 2.0 - 4.5 wt% C

Low alloy < 5% C < High alloy

NOTE: alloy additions increase cost. justified only by essential improvements in properties such as higher strength or improved corrosion resistance.

comprise the majority of ferrous alloys due to moderate price, due to the moderate amount of alloying and are sufficiently ductile.

high strength, low alloy. meets requirement of weight reduction... hot rolled allows for some stress.

absence of grain boundary help make them easily magnetized. potential for increased strength, toughness, and corrosions resistance. 

Amorphous metals.

Nonferrous

low density, corrosion resistance, electric conductivity, ease of fabrication, good appearance. 

Al-Li - increased stiffness

oxide coating makes for corrosion resistance, more dense than other mats, low ductility, high strength. 

hcp -- less slip systems -- lower ductility.

good ex of solutions hardening... strengthening by restriction of plastic deformation due to solid solution formation.

high temp strength, good resistance to corrosion

good for die castings due to low melting point and lack of corrosive reaction with steel

galvanization: zinc coatings on ferrous alloys, provides corrosion protection.

Crystalline Ceramics:

Silicates, nonsilicate oxides, nonoxides

Glasses - noncrystalline materials:

silicate, nonsilicate

Glass- Ceramics

abundant and economical

whitewares - fine grained micro structure

clay - like pottery

refractories - high temp resistance

Alumina and Magnesia

pure oxides - compounds with impurity levels less than 1 wt% (Expensive!)

magnetic ceramics represent the largest part of the industrial ceramic market.

Silicone Carbide, Silicon Nitride

withstands ULTRA high temps