ME3210 Chapter 3: Materials

Metals and alloys bonding type

metallic

Metals and alloys microstructure

crystal grains

Metals and alloys advantages

strong, ductile, conductive

Metals and alloys disadvantages

fracture and fatigue

Polymers bonding

covalent and secondary

Polymers microstructure

chain molecules

Polymer advantages

low cost, light weight, resist corrosion, good electrical insulators, and long-lasting color

Polymer disadvantages

low strength, low stiffness, creep, and low operating temperature

Ceramics and glasses microstructure

crystal grains and amorphous

Ceramics and glasses advantages

strong, stiff, resist temperature, resist corrosion, higher strength in compression, heat and electrical insulator, less expensive as raw material

Ceramics and glasses disadvantages

brittleness, more expensive to manufacture(diamond tooling), low tensile strength

Composites bonding

various

Composites microstructure

matrix and fiber

Composite advantages

strong, stiff, high strength to weight ratio, corrosion resistant

Composite disadvantages

high cost, delamination, more difficult to repair, high temperature sensitivity

Metallic Bonding

outer shell of electrons are given up to a common cloud where the atoms become charged and are held together by their mutual attraction to the electron cloud

Annealing

Heating metal allowing new crystals to form within the solid material, reducing grain size and elevating strength. More heating reduces strength.

Solid solution strengthening

Alloying elements forming a solid solution with the major constituent to impede the dislocation motion

For solid solution strengthening where are the alloying located

may be located at interstitial or substitutional transformational lattice positions

For solid solution strengthening effects

Higher solution percentage leads to more strengthening and the effect of size difference is not clear

Irons and steels

ferrous alloys of iron, and other alloying element

Aluminum alloy uses

Packaging, transportation, building/architecture, high pressure gas cylinders, machined components

Titanium Alloys have a

high strength to ratio, so it is used in aircraft, transportation, and sporting equipment

Titanium Alloys have excellent

corrosion resistance so they are used for chemical processing, power generation equipment

Polymers are

materials consisting of long-chain molecules produced primarily by carbon-to carbon bonds, such as plastics, natural and synthetic fibers, rubbers

Thermoplastics

softens and melts when heated. If cooled, it returns to its original solid properties

Thermosets when heated will change

chemically. It will not melt nor soften upon reheating, but will instead decompose, as by charring or burning

Thermosets are very

elastic and rubbery. It can be deformed by 200% strain or more elastically

Atomic Structure of Polymers

Mostly synthetic organic resin, which is a compound containing carbon as the central element

Saturated compound

has all the valence bonds of the carbon atoms satisfied

Unsaturated compound

has unsatisfied valence bonds of the carbon atoms

Difference between monomer and mer

Monomer has double bond mer does not

What is a mer

the smallest unit with all bonds satisfied

Polymerization

With proper pressure, temperature, and catalysts, a number of ethylene molecules with unsaturated bonds join together to form a long-chained molecule

At high temperatures thermoplastic polymers

secondary bonds melt so the long chains flow and the polymer loses its rigidity and strength (glass transition temperature)

Thermosets are generally

stronger, harder, more resistant to solvent, but higher in material cost

At Tg in thermosets the

primary bonds are broken by heat and the polymer decomposed. Reheating cannot restore the shape, structure, and properties

Elastomers

Natural or synthetic rubbers with very large elastic strain

Vulcanization

crosslinking elastomer polymer chains—most often with sulfur and heat—to form a three‑dimensional network that greatly improves strength, elasticity, and durability

Composites are

A macroscopic combination of two or more distinct materials with a recognizable interface in-between to form an overall structure that is better than the individual components

Matrix

metal, polymer, and ceramic matrix.

Reinforcement form

particulate, fiber, whisker, and laminar (fabric) composites

Purpose of reinforcement for metal matrices

to improve electrical resistance and toughness

Purpose of reinforcement for polymer matrices

to improve high temperature creep and hardness

Purpose of reinforcement for ceramic matrices

to improve toughness

Material cost fluctuations myths

materials always appreciate in time and short term fluctuations are caused by supply and demand

Material cost fluctuations reality

there are no definite time trends and volatility can largely be attributed to non-commercial factors

When cost estimating for competitive bidding

absolute cost wanted, to ±5%

Precipitation Hardening

Fast-cooling to trap a supersaturated solid solution, then reheating to grow fine precipitates that block dislocation motion