Material Selection Midterm 1

What is the starting material used to refine aluminum?

bauxite

Bauxite undergoes the ____ Process to get alumina

bayer

Alumina undergoes the _____-______ Process to get aluminum

hall-heroult

Aluminum has a ____ or _____ yield strength than most structural materials

similar or lower

Aluminum generally has ______ fracture toughness than most structural materials

lower

Aluminum generally has a _____ elastic modulus than most structural materials

lower

Aluminum has a significantly ____ density than most structural materials and thus _____ specific strength (strength-to-weight ratio)

lower, high

How much of all aluminum ever produced still in use today?

75%

When making steel, you need 2 raw materials: _____ and _____, you also add oxygen to reduce the carbon content to approximately ___%

iron and carbon, 0.04

Specialty stainless steels can only have ~__-__% Fe content

60-70

To produce elemental iron, you need iron in the form of ______, carbon in the form of ____, and calcium in the form of ____.

iron ore, coke, lime

When making iron in a blast furnace, you need ____ to melt the ore and ___ to remove impurities.

fuel, flux

Blast furnace reaction:
Fe_O_+3CO → __Fe + 3CO2

23, 2

What are the impurities that float to the top of molten iron in a blast furnace?

slag

What does a blast furnace produce?

pig iron

Why can’t you use pig iron?

4%C, too brittle

To refine pig iron and make steel, you add ___ in a basic ____ furnace. What does the carbon content reduce to?

oxygen, 0.04%

Compared to a BOF, an electric arc furnace can only use _____ _____ or ________.

scrap steel, direct reduced iron

Once steel is made, it undergoes a secondary refining to promote _____ and ____ homogenization and lower ____ levels.

temperature, composition, impurity

Austenitic steels (___ series) are non-magnetic, have excelllent corrosion resistance, and great formability. What is a common application?

300, kitchen appliances

ferritic steels (___ series) are magnetic, good corrosion resistance in mild environments, and are cost-effective. What are two common applications?

400, exhaust systems, architectural trim

martensitic steels are magnetic, have good wear resistance, and are easily hardenable. what is a common application?

cutting tools

What type of steel is most commonly used in aerospace parts?

precipitation hardened

Steel has a _____ elastic modulus than most structural metals

higher

During a uniaxial tensile test, the specimen is elongated in one direction at a fixed _____ rate

displacement

In a stress-strain curve, the slope in the elastic region represents a materials ___ ____.

elastic modulus

The ultimate tensile strength occurs at the onset of ____, or non-uniform deformation.

necking

What property quantitatively describes the energy required for fracture or, alternatively, the amount of energy that can be absorbed before fracture

fracture toughness

Combination of 2+ materials that have better properties than the individual components

composites

_____, or binder, surrounds the reinforcement to maintain positioning. It (is/is not) responsible for primary strengthening and stiffness.

matrix, is not

_____ provides improvements in material properties like stiffness and strength

reinforcement

In a fiber-reinforced composite, the fibers are _____

continuous (aligned)

in a fiber-reinforced composite, the fibers are _____

discontinuous (short)

In a polymer matrix, using ______ resins (epoxy, unsaturated polyester, and vinyl esters) results in brittle composites with relatively low strain to failure.

thermosetting

In a polymer matrix, using ______ resins need to be able to mold near RT and have a higher strain to failure.

thermoplastic

______ resins are infiltrated into preformed fiber with hardner and undergo chemical crosslinking in curing.

thermoset

______ resins are not crosslinked so their strength comes from the inherent properties of the chain.

thermoplastic

what are the 4 steps it takes to complete the material selection process?

translation, screening, ranking, documentation

What are the four things to keep in mind during the translating step of the material selection process?

function, constraints, objective, free variable

What are the three indices that combine to make an objective function?

functional requirements, geometric parameters, material properties

An Ashby plot is a plot of materials by ______ and _______

density, youngs modulus

What variable do you utilize to incorporate constraints into an objective function?

free variable

A material index shows up on an Ashby plot as a fixed _____.

slope

During the documentation part of material selection, you must research case studies and consider the ease/cost of ________ and environmental impact.

manufacturing

You use composites because they can be optimized to have ideal properties in certain _______ and are significantly ______ than traditional metals.

directions, lighter

What are the two types of structural composites?

Laminate (layers) and sandwich

When using metals as a matrix in a composite, it must be injected into the preform at ___ temperature without damaging the fibers (_____ casting). Low volume fractions of chopped fibers can be stirred into melt or fabricated using powder metallurgy.

high, squeeze

The usage of metals as a matrix in a composite results in a ______ stiffness increase over the base material compared to polymer matrix composites because unreinforced metals already possess a _____ baseline elastic modulus.

smaller, high

Metal-matrix composites have improved time-dependent properties like _____ and ________ by the addition of reinforcement.

creep, wear resistance

To calculate the mechanical properties of composites (focusing on continuous fibers), the properties will be bounded by isostrain (stress ____ to fiber alignment) and isostress (stress _____ to fiber alignment).

perpendicular, parallel

In a non-continuous fiber reinforced composite, you have to account for the _____ of the fiber.

length

In a non-continuous fiber reinforced composite, the black line indicates ____ stress while the red line indicates _____ stress.

tensile, shear

Metals used in composites tend to be _____ in comparison to bulk alloys.

ductile

In this step, the design requirements for a given component are transferred into a set of constraints, objectives, and free variables to enable desired functions

translation

This step applies the constraints developed during the Translation phase to remove materials that are unable to meet the lower-bound requirements for the components

screening

Screening provides a list of the materials that can do the job, but the role of this step is to quantitatively identify which materials are best for the job

ranking

This step often involves assessments of costs and suppliers, usage case studies, analysis of prior failures, evaluation of other considerations (e.g., corrosion)

documentation

Material indices (do/don’t) vary on the specifics of the component being designed

do

A single index line corresponds to a fixed value but its tangent lines can help create a ranking. If the material index is M = E/p, then M = 2 has the same modulus with 10 times ___ density than M = 0.2!

less

Titanium can have ____ alloying fractions

large

Raw materials for titanium production include….

rutile and slag

Step 1 of titanium production: _____, uses raw materials for titanium and calcined ____ to produce crude titanium tetra_____

chlorination, coke, chloride

Step 2 of titanium production: _____

distillation

Step 3 of titanium production: ______ and vacuum separation, titanium tetrachloride is reduced by ______ to produce titanium _____

reduction, molten magnesium, sponge

the magnesium chloride produced in step 3 of titanium production can be separated into magnesium and chlorine by…

electrolysis

Separating MgCl into Mg and Cl using electrolysis is very energy efficient (T/F)

f

Ti has a higher specific strength than Al and steel at ___ temperatures

high

Repeating units of organic chain molecules are called ____, bonding between them is ______

mers, covalent

The number of covalent bonds that each mer can form = _____

functionality

Mers that have the same chemical formula but different structures

isomers

a polymer which consists of only one type of mer

homopolymer

a polymer which consists of two or more types of mers

copoylmer

As the crystallinity of a polymer increases, density ____ and thermal softening ____.

increases, reduces

_____ have no cross-linking and are held together by van der waals bonds. They can be reversibly softened and partially crystalline.

thermoplastics

_____ are formed by mixing two components, permanent hardening. Extensive cross-linking and almost always amorphous.

thermosets

_____ are almost-linear polymers with branched cross-links. Capable of extremely large elastic strains.

elastomers

In polymers, increasing temperature correlates to ____ elastic modulus, _____ strains at fracture, ____ in flow stress.

decrease, increased, decrease

Viscoelastic behavior is determined by rate of strain, _____ for rapidly applied stress and ____ for slowly applied stress

elastic, viscous

Ceramics are much stronger in ______ than they are in (compression/tension).

compression

Ceramics have ___ resistance to crack propagation.

low

Melting temperature, elastic modulus, and polymer strength depend on what

molecular weight

Features of the glassy plateau:

• modulus is constant and at a _____

• polymers behave in a ____ manner

• Stiffness is based on the number of covalent bonds versus secondary bonds

• Secondary transitions in the plateau could be due to limited mobility of side groups causing ____

maximum, brittle, relaxation

What is glass transition:

• As the temperature increases, the _____ bonds connecting the polymer chains will start to melt

• Segments can then start to “slip” relative to each other, causing the modulus to ____

• Polymer also begins to expand, causing an increase in free volume (or decrease in density)

• In this region, deformation is recovered by non-sliding regions “pulling” back on the polymer – time dependent!

secondary, decrease

What is the rubbery plateau:

• Chance entanglements provide anchors → load and unwind, unload and rewind

• Rubbery behavior more pronounced with small amount of cross-links: ____

• However, if you have too many cross-links, unable to unwind and the rubbery behavior is limited → causes ____ in modulus and _____ temperature range of plateau

elastomers, increase, increase

What is viscous flow:

• At increased temperature, approaching __Tg or so, the secondary bonds have completely melted

• Entanglement points in linear polymers also slip; ____ don’t melt though – why?

• This region is also called “rubbery flow”

1.4, crosslinks

A design requirement should not specify how the solution should be obtained

solution neutral

In steel designations, (A) = ________, (B) = ______

type of material, carbon content

Most technologically relevant Ti alloys end up in the _____-_____ regime, leading to the ability to create a wide range of microstructures

alpha-beta

Ti alloys can be used at ____ service temps than Al alloys, but not “_____” than steels

higher

Ti alloys (do/don’t) maintain high specific strength at high temps, whereas Al alloy strength ____ at high temps

do, drops

Nickel alloys are generally broken into two categories: ______ or _______

solid solution, precipitation hardened

Nickel alloys have a ____ range of possible strengths and generally have ___ fracture toughness values

large, high

Bonding between polymer chains is _____ or ______

secondary (H-bonds, van der waals, or dipole-dipole) or covalent crosslinking

What properties do the degree of crystallinity, molecular weight, and degree of crosslinking effect?

all

1) The glassy region: Below ___, where side groups may rotate and slightly ____ modulus

Tg, decrease

2) The glass transition region: Around Tg, where macromolecules move and break ____ bonds, sharply ____ the modulus

secondary, decreasing

3) The _____ region: Above Tg, polymers with long chains resist shape change due to entanglements

rubbery

4) The viscous region: >___ Tg, linear polymers are viscous liquids

1.4

(5) The decomposition region, where the breakdown of _____ _____ bonds begins

covalent backbone