MSE 2001 Exam 3 Studyguide

What effective charge would an oxygen vacancy have in a MgO lattice?

+2 effective charge

Polymers are just a chain of repeat molecular units called

Monomers

The most likely mechanism for creep in a material under high tensile stresses is:

Dislocation motion (climb).

Hydrogels

Dry state shrunken reversible swollen state

Linear Defects (1-D):

Edge dislocations, screw dislocations. (A "line" of atoms that is misplaced)

Refractive Index

Electron Density of a Material (e-/volume) (Clausius-Mossotti Relationship) depends on atomic density and atomic number of elements

True/False: Hydrogels dissolve in water.

False

True/False: If two glasses have identical compositions, they will also have identical properties.

False Glasses are a non-equilibrium state of matter, so how you process them affects their structure and properties. We showed that faster or slower solidification of a glass from a melt affects its properties.

True/False: Systems containing only amorphous solids CANNOT have more than one phase.

False It is possible to have an amorphous solid with two phases of varying composition. One example is Pyrex, which has two amorphous phases: an SiO2-rich and a B2O3-rich one.

Creep Regimes with Time

First Section Elastic Strain & Primary Creep Second Section Steady-State Creep (Linear) Third Section Tertiary Creep & Fracture

How might Na substitutional impurities in a MgO lattice be charge compensated to reach charge neutrality?

Form 1 oxygen vacancy for every 2 Na impurities.

Which element would NOT act as a dopant for silicon? Boron Germanium Antimony Gallium

Germanium

Ceramic glasses A and B have the same composition but glass A has a higher fictive temperature than glass B. What could be accurate about these two glasses?

Glass A was quenched from a higher temperature than glass B, leading to glass A being less dense than glass B.

Assume that Glass A and Glass B are identical in composition and fictive temperature, but Glass A has many cracks of up to 2 mm maximum length while Glass B only has a few cracks with maximum lengths of < 1 mm. Based on this knowledge, which of these statements is most likely true?

Glass A will fracture at a lower critical stress than Glass B but have the same fracture toughness (KIc) as Glass B. Fracture toughness (K1C) is a materials constant, so it does not change since the glasses are essentially the same composition and structure (fictive temperature). Critical stress to failure (sigma*) would go down for A because of the longer cracks.

Planar Defects (2-D):

Grain boundaries, stacking faults, interphase boundaries, surfaces (boundaries or planes of atoms misplaced)

Failure of knowing Tg of polymer

Richard Feynman Challenger Disaster

"Ideal" yield strength

Shearing of a material could occur by simultaneously breaking all of the bonds in a plane.

Slip Systems

Slip Plane + Slip Direction •The greater the number of unique slip systems in a material, the easier it is to plastically deform (mostly true) •Slip systems must intersect one another, otherwise properties will be severely anisotropic (e.g., HCP) •To be counted as a unique slip system, slip planes must not be parallel and slip directions must not be colinear

What structural features will make a polymer more likely to crystallize?

Small side groups ( Large side groups prevent efficient chain packing.) low branching density Tacticity: isotactic or syndiotactic short repeat units hydrogen bonding or polar side groups

FCC {111}<110> 12 Slip Systems

most ductile of the metal crystal systems all slip planes are close packed slip systems intersect in 3D

n-type semiconductor

negative- e-

Thermosets include_____________ that can bond to 3 or more monomers

network forming monomers

at room temperature is glass still a liquid? -i.e., if we wait a really long time (like hundreds of years) will glass window panes flow to the bottom?

no It's just the result of how glass used to be manufactured entirely by hand using a punty iron. today's window pane's are float glass

Tacticity

-Isotactic -Syndiotactic -Atactic

grafted copolymer

different chains coming from main chain

This Mg-Zn-Al Alloy is...

two phase

Ionic addition polymerization is another form of addition polymerization -similar except

"ions" drive the addition.

chain growth polymerization

'Monomer' unit becomes part of the 'polymer' chain 'one at a time'

Compared to a completely amorphous polymer of the same composition, a semi-crystalline polymer is expected to: (I) have greater optical transparency. (II) show improved stability to higher operating temperatures. (III) appear more uniformly colored after dying. (IV) exhibit a higher elastic modulus. (V) be a better vapor barrier when used in food packaging.

(II), (IV), and (V)

What would be the effective charge of a Na substitutional impurity on a Mg site in MgO?

-1 effective charge

Molecular Weight

-Degree of polymerization -Chain length

Co-polymers

-Random -Block -Grafted

Adding a PbO modifier to SiO2 glass will result in a new glass that has...

...a higher refractive index and a lower glass transition temperature than pure SiO2 glass.

Fracture is a direct result of...

...crack propagation in a material.

In most metals, plastic deformations at room temperature caused by loads greater than the yield stress are the result of...

...dislocation motion.

Assume you load an engineering alloy (metal) past its yield point (without reaching its ultimate tensile strength) and then unload. The next time you load the material, it will...

...have a higher yield strength because it has been work hardened.

Wooden 4 inch x 4 inch x 12 feet wooden posts hold up the deck that comes off the second floor of your house. On the ground level, you decide to drill 1 inch holes in two of the posts in order to hang a hammock. Compared to the other posts, the posts that now hold the hammock...

...have a lower load bearing capacity because of the stress concentration near the holes.

The yield strength observed in a crystalline material at low homologous temperatures...

...is often orders of magnitude lower than the "ideal yield strength" of a material because plastic deformation occurs by dislocation glide.

You will definitely have low confidence in your prediction of the time to product failure if:

...the shaper parameter (beta) of the Weibull distribution is equal to 1. The shape parameter determines how sharp the transition is between parts not failing versus failing. When beta is much larger than 1, this transition is very sharp, and so the time to failure is well defined. If the shape is broader, you have parts that fail at all different times, and so it becomes hard to predict the product's lifetime.

You can be highly confident in your prediction of the time to product failure if:

...the shaper parameter (beta) of the Weibull distribution is much greater than 1. The shape parameter determines how sharp the transition is between parts not failing versus failing. When beta is much larger than 1, this transition is very sharp, and so the time to failure is well defined. If the shape is broader, you have parts that fail at all different times, and so it becomes hard to predict the product's lifetime.

How are defects in materials classified?

0d - point defect 1d - linear defect 2d - planar defect 3d - volume defect

If Ca impurities are added to TiO2 and form substitutional defects on the Ti sites, what type of defect might form to charge compensate for them and in what ratio? 1 Ti vacancy : 2 Ca impurities 1 Ti vacancy : 1 Ca impurity 1 oxygen vacancy : 1 Ca impurity 1 Ti interstitial : 1 Ca impurity 1 oxygen interstitial : 1 Ca impurity

1 oxygen vacancy : 1 Ca impurity With calcium on a titanium site, titanium has a +4 charge and calcium will only have a +2 charge, so the Ca will adopt an effect -2 charge. Vacant oxygen sites are expecting a -2 charge, so they have an effective +2 charge. Thus 1:1 these two point defects will compensate each other.

You own a brass tuba composed of 90% copper and 10% zinc. Brass is a substitutional solid solution of copper and zinc. How many phases make up your brass tuba?

1 phase

Crystallinity in Polyethylene terephthalate (PET)

1. Amorphous PET made by injection molding -Optically transparent 2. Partially crystallized PET due to poor quenching (interior remains hot & crystallizes) -get translucent material 3. Powder processed PET formed by compressing highly crystalline PET powder -Crystals are ~1 micron in size leading to light scattering (opaque / white).

Mechanisms for strengthening Materials

1. perfect lattice 2. fss solution hardening 3. fppt precipitate hardening 4. fwh work hardening

Types of Polymerization Reactions:

1.. Chain Growth / Addition Polymerization -Free radical polymerization -Ionic addition polymerization 2. Step Growth / Condensation Polymerization

What might you try to do to increase the yield strength of a metal rod: (3 things)

1.Process the alloy in such a way to achieve 50 nm sized grains. 2.Add more impurity elements to the alloy. 3.Cold draw the metal rod to a smaller diameter.

How many INDEPENDENT SLIP SYSTEMS are in an FCC metal?

12

Guinier-Preston (GP) Zones in Aluminum Alloys

2 phases

White latex paint is an emulsion of acrylate monomers, an iniator, and TiO2 particles that scatter light to give the white color. While drying on the wall, initiators are released and polymerize the monomers into a latex polymer. Excluding the initiators (which effectively become part of the polymer), how many phases are in dried white paint?

2 phases

How many unique slip systems? (Slip direction family is <110>)

3 slip directions * 4 unique slip planes = 12 slip systems

How many INDEPENDENT (non-parallel) slip planes are in an FCC metal?

4

What does "The atomic structure of a metal-supported vitreous thin silica film, Angewandte Chemie International Edition5 1, 404-407 (2012)" show?

Atomic Imaging of SiO2 Glass by TEM crystalline -> noncrystalline

Titanium dioxide (TiO2) is deposited as an amorphous thin film. When annealed, 75% of the film crystallizes. X-ray diffraction analysis reveals that these crystals are a mix of rutile, anatase, and brookite -- three different crystal structures of titanium dioxide. At this point, how many phases are in the TiO2 thin film?

4 phases -- the three different crystalline forms of TiO2 and the amorphous TiO2.

How Many Unique Slip Planes are in an FCC Crystal? (Slip plane family is {111})

4 unique slip planes (111) (-111) (1-11) (11-1)

How many unique slip planes of the {110} type are in a BCC metal?

6 (110), (101), (011), (-110), (-101), (0-11) -- the negatives of these are not unique, and I only asked for the {110} family not for the {112} and {123} families.

Charpy Impact Test

A destructive test of impact resistance, consisting of placing a test coupon in a horizontal position between two supports, then applying a blow of known magnitude. If the specimen does not break, a new specimen is put in position and the magnitude is increased until the specimen breaks.

Fatigue

A fracture based failure due to repetitive or cyclic loading.

thermoset polymer

A polymer (usually composed of a three-dimensional network of covalently bonded atoms) that does not melt when reheated. Ex. Monomer C has 3 functional groups with which to make a network structure. With only 2 functional groups, only linear chains can be guaranteed.

Based on these descriptions, which of these polymers is MOST likely to crystallize. A polymer with large, isotactic side groups and significant branching. A polymer with large, atactic side groups and significant branching. A polymer with small, syndiotactic side groups and no branching. A polymer with small, atactic side groups and no branching. A polymer with large, syndiotactic side groups and no branching. A polymer with large, syndiotactic side groups and significant branching.

A polymer with small, syndiotactic side groups and no branching.

Thermoplastic

Above Tg: moldable and liquid like Below Tg: Rigid solid, tough Heating Process: melt into aligned and reversible

Which of these statements is NOT true about glasses? Adding chemical modifiers to SiO2 glass increases the amount of bonding in the glass network and usually raises the glass transition temperature. Adding chemical modifiers with high atomic number to an SiO2 glass will usually increase the refractive index of the glass. Cooling a glass melt faster can lead to forming a glass with a higher fictive temperature. If you change the chemical composition of a glass, you will likely change the glass transition temperature of that glass. Glasses of the same composition but different fictive temperatures can have different thermal conductivities.

Adding chemical modifiers to SiO2 glass increases the amount of bonding in the glass network and usually raises the glass transition temperature.

Monomers & Their Polymers: Chain Growth

Addition Polymerization

Step Growth is to Condensation Polymerization as Chain Growth is to

Addition Polymerization

Working as a consultant for an engineering firm, a steam plant manager comes to you for advice. He intends to lower the temperature of the steam running through his steam pipes, but maintain all other operational conditions the same (i.e, steam pressure inside the pipes and the cycling schedules for pressurization and depressurization ). He asks you how this change might affect the serviceable lifetime of the steam pipes. All of the following replies are accurate EXCEPT: The lower temperature will decrease the creep rate, decreasing the risk for creep failure. By not increasing the pressure in the steam pipes, you will not increase the risk for yielding the material. By maintaining the same pressure cycling schedule, you will retain about the same fatigue rate as before, and, thus, your risk for fatigue failure will remain the same. All are accurate

All are accurate

Two metal alloys are nearly identical, except Alloy A has 2% impurity content and Alloy B has 8% impurity content. Assuming lattice resistance is nearly zero for both alloys, what do you predict the difference in yield strength (sigma)y to be for these two materials?

Alloy B will have a 2x higher yield strength than Alloy A. Concentration increases by 4x, and shear strength scales by the sqrt(concentration), so the shear strength increases by 2x. The conversion to yield strength (3x) cancels out when comparing the two materials.

Where does dislocation glide occur?

Along the Path of Least Resistance!

Which of the following would be a good p-type dopant for the semiconductor silicon? A. Phosphorus B. Arsenic C. Aluminium D. Germanium Both A & B Both C & D

Aluminium

Losego et al., Appl. Phys. Lett. 104, 253107 (2014)

Amorphous Oxide Thin Films refractive temperature vs growth temperature thermal conductivity vs atomic density

Which of the following is/are example(s) of 2D defect(s) in a crystalline material? (A) Dislocations (B) The surface of the material (C) Grain boundaries (D) Inclusions (B) and (C) (A) and (C) (A) and (D) (A) and (B) (B), (C), and (D) (A), (B), (C), and (D)

B and C

Which element would create electronic "holes" in silicon? Boron Phosphorous Germanium Arsenic Both Arsenic & Phosphorous

Boron

Which of the following would increase the time (number of cycles) to fatigue failure in the given material? (A) Flame polishing the surface of a glass component. (B) Cold working a metal alloy. (C) Shot peening a metal gear. (D) Reducing the use temperature of a polymer component to below its glass transformation temperature.

Both (A) and (C)

Which of these components when loaded to below its yield strength is likely to suffer a creep failure at room temperature (25 °C) operation? (Choose the BEST answer.) (A) A steel cable holding up a suspension bridge. (B) A nylon cable suspending a yacht from the ceiling in a dry dock. (C) A solder joint under tension from the wire bond on a circuit board.

Both (B) and (C)

The Burgers Vector & How to Locate It

Burger Vector indicates the magnitude and direction of the displacement 1. Draw a clockwise loop in a perfect crystalline lattice, counting & recording the unit cell dimensions for each side of the loop (shown in the boxes). 2. Draw the same loop (with the same lengths for each side) around the dislocation. 3. The vector required to close the loop is the Burgers vector. (i.e., the direction and distance that a dislocation will plastically deform a lattice with its motion.)

Which type of rubber do you think has more cross-links (i.e. more cross-links per volume)? Rubber bands or Car Tires

Car tires

To measure the fracture toughness of a material, the best technique to use is:

Charpy Impact Testing

The filament in an incandescent lightbulb is especially susceptible to failure via:

Creep

Thermoplastics vs. Thermosets

Cross-linking (Network)

Crystalline Spherulites

Crystalline regions can organize further into what are known as "Spherulites". Often formed when linear thermoplastic polymers are solidified from a pure melt.

Kitamura et al. J. of Appl. Phys. 101, 123533 (2007) shows what relationship of glass?

Here is an examples of differently prepared SiO2glasses where both the mass density and refractive index were measured. These two properties have a clear linear relationship- the higher the density the higher the refractive index

Grafted polymer

How would you best describe the structure of this polymer? (Assume the different colored spheres represent different monomer chemistries.)

Syndiotactic

In polymers, an orientation where the side groups alternate in a regular pattern from side to side along the backbone of the polymer. What kind of tacticity does this polypropylene chain have?

Assume you are making aluminum alloy components and TiB2 grain refiners are being used to achieve 10 micron sized grains. You want to try to increase the yield strength of the alloy by decreasing the grain size to 1 micron. Which of the following would you suggest to achieve a smaller grain size?

Increase the concentration of TiB2 powder in the molten metal melt before casting.

What are Modifiers?

Modifiers are elements that don't form 3+ covalent bonds with oxygen. oftem alkali and alkaline earth metals Common modifiers include: Na, Ca, K, Mg, Sr, Ba, Pb, Li.

How do polymers have short range order?

Monomers

Stainless steel is a metal alloy commonly containing Fe, Cr, Ni, and C and has an atomic structure sort of similar to what is schematically pictured above. Iron is the major component in steel. Chromium and nickel sit on substitutional sites of the iron lattice. Carbon sits at interstitial sites of the iron lattice. A schematic depiction of this atomic arrangement is shown above. Based on this description and the picture shown above, how many phases exist in this stainless steel?

One phase

Cross-Linking Rubber- Vulcanization Natural Rubber (Polyisoprene) ->

Synthetic Rubber (Polybutadiene)

Common Thermoplastic

PET

Improving Fracture Toughness

Polish out surface cracks Increase residual compressive stresses at the surface Increase surface hardness Avoid macroscopic stress concentrators

Acrylonitrile Butadiene Styrene (ABS)

Polymer Blend 3 monomers

Step Growth Monomer: Polymer Diamine + Dicarboxylic Acid = Amino Acid = diisocyanate + diol =

Polymer: Nylon Polypeptide Polyurethane

Monomer: Vinyl Chloride

Polymer: PVC

Monomer: Styrene Polymer:

Polymer: Polystyrene

Monomer: Methyl methacrylate creates Polymer

Polymer:PMMA

Which of these polymers is LEAST likely to crystallize? Polypropylene [C2H3(CH3)]n Polyethylene [C2H4]n Polysytrene [C2H3(C6H5)]n Polyvinyl chloride [C2H3Cl]n

Polysytrene [C2H3(C6H5)]n Polystyrene has the large side group.

Volume Defects (3-D):

Pores, cracks, inclusions (a bulk defect)

What is a phase?

Portion of a material that has a homogeneous structure and composition

How is the network structure formed?

Primary covalent bonds making thermosets more rigid than thermoplastics.

Which of the following statements is true about how the equilibrium vacancy concentration is determined in a material? The ENTHALPY of vacancy formation accounts for the increased disorder due to vacancy formation and acts to increase the concentration of vacancies in a material while the ENTROPY of vacancy formation accounts for bond breakage and acts to lower the concentration of vacancies in a material. The ENTHALPY of vacancy formation accounts for bond breakage and acts to lower the concentration of vacancies in a material while the ENTROPY of vacancy formation accounts for the increased disorder due to vacancy formation and acts to increase the concentration of vacancies in a material. The ENTHALPY of vacancy formation accounts for bond breakage and acts to increase the concentration of vacancies in a material while the ENTROPY of vacancy formation accounts for the increased disorder due to vacancy formation and acts to decrease the concentration of vacancies in a material.

The ENTHALPY of vacancy formation accounts for bond breakage and acts to lower the concentration of vacancies in a material while the ENTROPY of vacancy formation accounts for the increased disorder due to vacancy formation and acts to increase the concentration of vacancies in a material.

What is a component?

The atomic or stoichiometric (molecular) constituent that makes up a phase. (not a phase)

Which of these components is the LEAST likely to suffer from a fatigue failure. The axel of a car. A diving board. The anchor cable for an offshore oil rig. The bricks in the external walls of a house. The fuselage of an airplane.

The bricks in the external walls of a house.

How would you define the "yield strength" of a material?

The critical stress required to permanently deform the material.

How does using single crystal turbine blades help reduce creep failures in jet engines?

The lack of grain boundaries in single crystals helps prevent creep.

How does using a single crystal metal turbine blade compared to using a polycrystalline metal turbine blade help to reduce creep failures in jet engines? The higher melting temperature of the single crystal material helps to prevent creep. The lack of grain boundaries in the single crystal material helps to prevent creep. The higher yield strength of the single crystal material helps to prevent creep.

The lack of grain boundaries in the single crystal material helps to prevent creep. Note that single crystals and polycrystalline morphologies of the SAME material will have the SAME melting temperature. The melting temperature is not really affected by grain boundaries; it is mostly determined by the bonding of the material. Also, single crystals (at least of metals) will likely have lower yield strengths than their polycrystalline counterparts, since the grain boundaries (if anything) will act as barriers to dislocation motion, increasing the yield strength.

he yield strength of 304 stainless steel is ~600 MPa, while the yield strength of diamond is > 1.2 GPa (i.e. >1200 MPa). Why?

The lattice resistance is higher in diamond.

Dislocation Guide

The true yield strength of a material is much lower than the ideal yield strength because only a single line of bonds is broken at a time to initiate and propagate the shear deformation (i.e., yielding of the material.

How do atoms that are above 0k show their thermal energy?

Through Vibrations

Hume-Rothery "Rules" for Forming Solid Solutions

To form a solid solution, the two (or more) elements must: 1....have atomic radii that are < 15% different from one another in size 2....have electronegativities that are comparable to one another. 3....have the same valence charge 4....have the same crystalline structure

Many shaping processes for metals involve plastically deforming the material into the desired shape. When "rolling" (or "drawing down") sheet metal from one thickness to another, annealing steps must often be added between each rolling step. (In other words, you can't always roll one thickness directly to a much thinner thickness; instead the sheet must be rolled to an intermediate thicknesses and then heat treated prior to rolling to the even thinner thickness.) Why is this annealing step necessary?

To remove newly formed dislocations.

Two examples of SiO4 tetrahedral that are corner-shared (i.e., same short-range order) and have LRO

Tridymite, Quartz

True / False: Increasing the temperature of the semiconductor germanium will increase the concentration of germanium vacancies in the material.

True

True / False: Substitutional point defects can be used to increase the electrical conductivity of a semiconductor.

True

True / False: When you plot failure rate data in the form of ln[ln(1/(1-P))] versus ln(N) where P is the cumulative probability of failure and N is the number of cycles, a linear fit to that data will give a line having a slope that we can use to estimate the shape parameter for the Weibull distribution of that data set.

True

True or False: Glasses are in a frozen liquid state.

True

True/False: Amorphous solids have short range order.

True

True/False: Polycrystalline materials have many mis-oriented crystalline grains in their microstructure because the phase transformations used to create these materials (e.g., solidification) occur via a nucleation and growth process.

True

True/False: Adding precipitates to a metal alloy will likely increase its yield strength but decrease its fracture toughness.

True While precipitates will increase yield strength of the alloy, this usually reduces the plastic zone at the crack tip, leading to reduced fracture toughness.

Which of these techniques could be used to probe the short range order in window glass?

Using x-ray scattering to collect a radial distribution function.

Which of these statements about point defects is true? Lowering the temperature of a material will NOT alter the concentration of point defects in a material. Vacancies do not need to be charge balanced in metals. Point defects cannot significantly alter the properties of a material. Oxygen vacancies in a ceramic have a negative effective charge. Point defects are always a non-equilibrium type of defect.

Vacancies do not need to be charge balanced in metals.

Point Defects (0-D):

Vacancies, interstitials, substitutional impurities, Schottky deffects, Frenkeldefects (misplacement of 1 or 2 atoms)

A higher cooling rate leads to

a higher cooling rate leads to a higher fictive temperature and a lower density of the glass

What is Glass?

a non-crystalline solid an amorphous solid a solid without long range order

Defect formation

a thermally unfavorable process (It raises the free energy of a system by adding enthalpy, i.e., it makes the free energy more positive) broken bonds internal strain

"Super balls" that bounce really high are an example of...

a thermoset polymer with its Tg below room temperature.

Thermoset

above tg: rubbery solid below tg: brittle and rigid solid heating process: decomposition and irreversible

What additional consideration must be made when considering point defect formation in ionic solids?

account for change

isotactic

all aligned

syndiotactic

alternating/back and forth

Slip Planes

are crystalline planes with the highest atomic packing density

Work of Fracture ("Toughness")

area under the stress strain curve

b-shape parameter

b< 1 -wide variability in failure rates, "infant mortality" or failure during "burn-in" period b= 1 -"constant" failure rate b> 1 -narrow failure distribution.

Which of the following would be a good n-type dopant for the semiconductor germanium? A. Phosphorus B. Arsenic C. Boron D. Silicon Both A & B Both A & C

both a and b

Point defects... (select all that apply) can alter the color of a material. must be charge balanced in ionic solids. can locally strain the crystalline lattice of a material. can increase the electrical conductivity of a semiconductor. have no appreciable impact on the properties of a material. must be charge balanced in metals.

can alter the color of a material. must be charge balanced in ionic solids. can locally strain the crystalline lattice of a material. can increase the electrical conductivity of a semiconductor.

Frenkel defect

combines interstitial and vacancies of the same ion

Thermosets

cross-linked polymers that form one giant molecule

Slip Directions

crystalline directions with the highest linear packing density

HCP {0001}<1000> 3 Slip Systems

fairly brittle metals only has three slip systems and all are parallels to one another

What makes a polymer be mechanically stronger?

high molecular weight

Creep is accelerated at

high temperature operation.

Crystallinity usually leads to:

higher elastic modulus (more rigid) higher melting (service) temperature higher opacity due to light scattering More difficult to dye because dye segregates to amorphous regions better vapor barrier properties because crystallites are more impermeable to gases.

Plastic Deformation in Crystals: Dislocation Glide: Impeding Dislocation Motion Vs Enhancing Dislocation Motion

impeding dislocation motion increases yield strength enhancing dislocation motion improves ductility

Which of the following will NOT improve the fracture toughness of a material? Carburizing the surface of a steel alloy. Shot peening the surface of a metal alloy. Flame polishing a glass component. Leaving bubbles trapped in a glass.

leaving bubbles trapped in a glass

p-type semiconductor

positive hole

Atactic

random position of side groups

BCC {110}<111>, {112}<111>,& {123}<111> 48 Slip Systems

reasonably ductile more slip planes than FCC in 3D but harder to move dislocations because not closed packed

What can be done with thermoplastics but NOT thermosetting polymers?

recycling

Tacticity

relative orientation/alignments of side groups on a polymer

Fracture Toughness (also "Toughness")

resistance of a material to crack propagation

Sodium chloride (NaCl, Salt) is:

single phase

Stainless Steel is:

single phase

Sugar water is:

single phase

This polycrystalline steel:

single phase

What happens to the refractive in tex of an SiO2 glass if modifiers like CaO and K2O are added to it? The refractive index will increase because the molar volume decreases. The refractive index will decrease because the molar volume decreases. Something else will happen.

something else will happen

Where Might Creep Occur?

steam pipes turbine blades filaments in light bulbs

Schottky defect

stochiometric vacancies on both the cation and anion sites

Increasing Chain Length Increases Secondary Bonding Between Chains -> Increased

strength

In window glass, silicon is

tetrahedrally coordinated to 4 oxygens.

Semicrystalline polymers are opaque because

the crystallites scatter light.

What can kinetically prevent solids from becoming crystalline from occurring?

the energy barrier to transform from an amorphous liquid to an ordered crystalline solid

How do modifiers bond with Oxygen?

they form more non-directional, weaker ionic bonds w/ higher coordination number.

My cloudy sweet tea (#2): Solid sugar & solid tea precipitates out of your sweet tea (90% water, 5% tea molecules, and 5% sugar molecules)

three phase

The glass transition temperature is always below the melting temperature of a material.

true

What is the true mechanism for plastic deformation in a crystalline material?

true mechanism : dislocation motion to plastically deform, you must apply sufficient stress to move dislocations 1st postulated in 1930's 2nd proven in 1950's

My cloudy sweet tea: Solid sugar precipitates out of your sweet tea (90% water, 5% tea molecules, and 5% sugar molecules

two phase

Total Yield Strength of Crystalline Materials

ty= tlattice+ tss+ tppt+ tdislocations+ tGB

Adding cross-links to a polymer will...

will make the polymer more rigid.

X-ray Diffraction Pattern of SiO2

without well-defined repeating crystalline planes, glasses scatter randomly in a "amorphous hump"

Do glasses/amorphous/noncrystalline solids have SRO?

yes

Which family of planes act as dislocation slip planes in an HCP metal? Use the three Miller index notation for this problem.

{001}

Which family of planes has the highest atomic packing density (atoms/area) in a BCC metal? {210} planes {111} planes {110} planes {100} planes

{110} planes

Which family of planes has the highest atomic packing density (atoms/area) in a FCC metal? {100} planes {110} planes {111} planes {210} planes

{111} planes

Slip System:

{slip plane family}<slip direction family>

Improving Fracture Toughness

• Polish out surface cracks (mechanical polishing of metals, flame polishing of glasses) • Increase residual compressive stresses at the surface (e.g., shot peening of a metal component introduces compressive stresses at the surface; thermal or chemical tempering does the same for glass.) • Increase surface hardness by changing the surface chemistry (e.g., carburization adds carbon to the subsurface of a steel component and increasing surface hardness & preventing cracks from forming) • Avoid macroscopic stress concentrators (e.g., notches, sharp corners, etc.)

Once the failure data is fitted, you can use a Weibull distribution function to...

•Predict the percent chance that a material will survive or fail in a given amount of time. •Determine a mean time to failure. •Calculate a "Reliable Lifetime" to be used for product warranties. •Plot the probability of failure with time or cycle number.

Creep

•Slow, continuous deformation due to the constant application of a modest load BELOW the yield stress. Creep typically occurs at 0.35 Tmfor elemental metals and 0.45 Tmfor ceramics(alloying can significantly increase these temperatures)