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College > Mats. Final > Flashcards

Mats. Final Flashcards

1
Q

Graphite, iron, quartz

A

Crystalline

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2
Q

BCC

A

Bold

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3
Q

Glass

A

Amorphous

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4
Q

oooooooo
oooooAooo
oooooooo
ooooobooo

A

A = Vacancy
b = substitution

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5
Q

Graphite in cast iron is an example of what type of defect?

A

precipitae

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6
Q

Dislocation definition

A

extra half plane of atoms

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7
Q

how are grain boundaries formed in crystals?

A

cooling from a liquid

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8
Q

when a metal/crystal is loaded in tension in elastic region, what’s happening to the atomic bonds?

A

bond length is getting longer “stretch”

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9
Q

what 2 criteria about a crystal need to be satisfied in order for material to be ductile?

A

crystal must have slip planes and dislocations

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10
Q

during ductile/plastic deformation of a metal/crystal loaded in tension, the planes of atoms are moving in response to what resolved stress?

A

shear

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11
Q

when we say that planes of atoms are slipping, what’s actually moving?

A

dislocations

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12
Q

All 4 strengthening mechanisms and defect/imperfection that makes material stronger

A

Solid strength hardening = subs.
Precipitation hardening = precipitates
Grain refinement = grain boundaries
Strain hardening = dislocations

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13
Q

T or F: Mechanisms used to make metals stronger also make them more brittle.

A

T

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14
Q

After grain refinement used to make metals stronger, what can you do to “erase” it or make it weaker again?

A

Annealing = heat up to a phase transition and cool again slowly

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15
Q

Steel is an iron-carbon alloy. There is a eutectoid transformation in alloys with 0.76% carbon. What phase
exists immediately above the eutectoid point and what phases exist below it?

A

Above E = gamma; Below E = alpha and Fe3C

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16
Q

what’s special about the microstructure that forms after a eutectic or eutectoid transformation?

A

it’s layered

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17
Q

what’s the melting temperature of pure iron?

A

1538 C

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18
Q

T or F: Austenite is a liquid

A

F but a FCC

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19
Q

What is the yield strength of a mild 1018/A36 steel?

A

36 ksi

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20
Q

Stress concentrations at crack tips are dependent on:

A

Crack length, Crack radius of curvature, Applied tensile stress

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21
Q

Name one factor that the stress intensity (KI) depends on

A

crack length, applied tensile stress, geometry

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22
Q

What happens to atoms in plastic deformation? (ductile)

A

planes of atoms “slip” in shear

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23
Q

Ductile materials have 2 components:

A

CPP and dislocations

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24
Q

How do dislocations exist?

A

Entropy

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25
Q

Dislocation motion?

A

visualize car driving down road as shear stress needed to move dislocation

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26
Q

Why is deformation important ?

A

Once broken & reformed a new bond, you would have to break it again to go backward

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27
Q

Why does slip happen only on close (or closely) packed planes?

A

CPP have shortest slip distance (break fewest bonds) “slip planes”

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28
Q

Step Process of Slip Planes

A

FCC have 3 intersecting CPP and have 12 slip systems
HCP have parallel slip planes and about 3 slip systems
BCC have 2 intersecting CPP and have about 12 slip systems

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29
Q

HCP brittle or ductile than rest?

A

Brittle

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30
Q

Alloying?

A

dissolving an impurity metal into majority metal

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31
Q

strengthening = hardening =

A

embrittling

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32
Q

Fe3C (cemenite) is ductile or brittle?

A

brittle

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33
Q

Smaller grain size =

A

more brittle (stronger) and cool faster

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34
Q

weakening = softening =

A

ductilifying

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35
Q

Component?

A

composition which is ingredients

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36
Q

phase?

A

structure which is how components are arranged in space

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37
Q

What’s ferrite?

A

alpha iron: BCC

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38
Q

Pearlite?

A

thinner the layers the faster you cool it and less time for diffusion

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39
Q

As C content increases…

A

strength increases, ductility decreases, and weldability decreases

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40
Q

43xx means…

A

nickel, cr, and maybe molybdenum

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41
Q

How does ductile mats. fail?

A

in yielding. when dislocations move along CPP due to resolved shear stress

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42
Q

How do brittle mats. fail?

A

in tension due to crack growth

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43
Q

Fracture when

A

Applied stress greater than or equal to stress bond break

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44
Q

Crack will grow when

A

max stress greater than or equal to stress bond break

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45
Q

fracture toughness =

A

KIC (stress = applied stress needed for cracks to start growing

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46
Q

Creep =

A

constant stress (strain reduces)

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47
Q

stress relaxation =

A

constant strain (stress reduces)

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48
Q

Fatigue =

A

cyclical load which is worried about tension

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49
Q

the longer the cracks…

A

the longer the stress concentration

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50
Q

fatigue limit can…

A

withstand infinite N, as long as S < fatigue limit

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51
Q

N is highly variable and…

A

dependent on flaws - change with specimens

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52
Q

Tresca

A

ductile mats. = max shear stress

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53
Q

Rankine

A

brittle mats. = max principal stress theory

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54
Q

Galvanic Couple

A

anode oxides and cathode reduces and get a voltage

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55
Q

Corrosive environments include

A

moisture containing dissolved O
Sulfur (acid rain)
NaCl (sea water)
Soil (damp)

56
Q

Types of corrosion

A

Uniform attack, galvanic corrosion (2 alloys/metals are electrically coupled), crevice and pitting, intergranular, stress corrosion, and H embrittlement in steel

57
Q

Corrosion Prevention

A

Paint, “passivation” (protective oxide barrier)

58
Q

Which of the following is an example of a material that has been strengthened using precipitation hardening?

A

Steel

59
Q

Why does making a metal stronger also make it more brittle?

A

Dislocations can’t move easily.

60
Q

Why are ductile mats. less crack sensitive than brittle mats.?

A

Plastic deformation at the crack tip increases the radius of curvature

61
Q

Why did zinc and copper pennies behave differently when hit by a hammer?

A

Some slip planes are inactive at cold temps

62
Q

When failure in fatigue happens in metals, we look
at the stress amplitude, i.e. the maximum tensile stress in the cycles of loading. Why do we look at the
maximum tensile stress and not the maximum compressive stress?

A

Tensile stress make cracks grow

63
Q

Why does the oxidation of silver or aluminum not cause extensive damage while the oxidation of steel does cause extensive damage?

A

Steels oxidation product flakes off and exposes new surface

64
Q

In galvanized steel, the steel is coated with

A

Zinc

65
Q

Why doesn’t steel reinforcement in concrete start rusting immediately after placement since concrete
contains water with dissolved ions?

A

The high pH of concrete pore solution prevents steel from forming rust

66
Q

Covalent Bond

A

A chemical bond involving the sharing of electron pairs between atoms is known as a covalent bond (H20, N2, CH4, H2, O2)

67
Q

Ionic Bond

A

the complete transfer of valence electron(s) between atoms (NaCl, NaBr, KF, KCl)

68
Q

Metallic Bond

A

Same chemicals mixed (Gold, Silver, Copper)

69
Q

Hydrogen Bond

A

Molecules that contain a hydrogen atom bound with fluorine, oxygen, or nitrogen are considered examples that show the hydrogen bonding process. (Water, ammonia, hydrogen fluoride)

70
Q

Why are the bonding energy and melting temperature linearly correlated for metals?

A

Because melting occurs when metallic bonds in metals are broken

71
Q

Bonds that share valence electrons?

A

Covalent and Metallic

72
Q

Bonds that have electrostatic attraction?

A

Ionic and Hydrogen

73
Q

When thermoplastic polymers melt…

A

H bonds between hydrocarbon chains break

74
Q

Propane and polyethylene (PE) are both only made of C and H. Propane has 3 Carbons in each molecule while PE has thousands. Why is propane a gas at room T while PE is a solid?

A

PE has more H bonds than propane

75
Q

Highest to Lowest most expected plastic deformation polymers?

A

Polyethylene, polystyrene, rubber

76
Q

Why is rubber elastic?

A

It has covalently-bonded cross-links between hydrocarbon chains

77
Q

Why is HDPE stronger and more brittle at -40°C than at room temperature (RT) and higher temperatures (i.e., what happens to the molecules at different temperatures)?

A

At lower temperatures the atoms have less vibrational energy, so the hydrogen bonds are stronger. When the hydrogen bonds are stronger, the material is stronger and more brittle because the chains cannot slip past each other to make plastic deformation

78
Q

Rubber bridge bearings and base-isolation systems are used to allow shear deformation of bridges and
buildings due to thermal expansion or earthquakes. These are considered polymer composite materials
where rubber is the matrix. What is the reinforcement material used?

A

Steel

79
Q

Fiber reinforced polymers (FRP) are used in a variety of civil engineering applications, for example as an
alternative to steel for reinforcing concrete. Why would you want to use FRP instead of steel rebars?

A

FRP does not corrode/rust

80
Q

In the FRP composites used in civil engineering, the fibers are:

A

Continuous through the material and aligned in parallel to each other

81
Q

In the FRP composites used in civil engineering, the matrix is

A

Epoxy/resin

82
Q

Carbon fiber-reinforced polymers (CFRP) are used to strengthen structural concrete members. To structurally strengthen a load-bearing column, in what orientation are the fibers applied relative to the
column?

A

Around the circumference of the column (transverse)

83
Q

Asphalt can come from either natural deposits or from crude oil. In the crude oil refining processes, asphalt is at the “bottom of the barrel” because

A

The hydrocarbons in asphalt have a higher molecular weight than the hydrocarbons in gasoline, the asphalt is a solid room temperature whereas gasoline is a liquid, and asphalt is a waste or by-product containing the molecules the other products don’t want

84
Q

Asphalt flows like a liquid at high temperatures and is a solid at room temperature because

A

It is a polymer, and the hydrogen bonds between chains break at high temperatures

85
Q

Which of the following asphalt deterioration mechanisms happens due to traffic loading when it is too hot outside for the asphalt binder used in the pavement?

A

rutting

86
Q

Asphalt pavements are designed using performance criteria. Which of the following is considered to be a design criterion used for designing the material to be used in pavements?

A

The behavior of the asphalt under the expected traffic loads

87
Q

Why is it easier to recycle an asphalt pavement into another asphalt pavement than it is to recycle a portland cement concrete pavement into another pavement? (In your answer, explain how asphalt
pavements can be recycled.)

A

Asphalt is recycled by heating it again, just like thermoplastic polymers. Cement cannot be rehydrated once it is hydrated - it is a one-way chemical reaction. You can re-place the asphalt in a pavement by heating again, melting it, and allowing it to cool and solidify. You can only reuse the
aggregate in concrete, not the concrete itself.

88
Q

Wood is a natural composite material made of polymer fibers with a polymer matrix. What polymer are the fibers made from?

A

Cellulose

89
Q

Assuming the fiber saturation point of wood is 26%, rank the following moisture conditions in order of
highest (1) to lowest (4) volume on the answer sheet. Write “=” between conditions that have the same
volume: 10%, 20%, 30%, 50%.

A

1) Highest 50% = 30% > 20% > 10% (4) Lowest

90
Q

For the moisture states in the previous question, which one would be the strongest in compression?
(There may be more than one correct answer, but just pick one.

A

10%

91
Q

Engineered wood composites combine wood pieces with polymeric glues to overcome some of the
shortcomings of natural wood. Name one shortcoming of natural wood that engineered wood solves

A

Size, defects, anisotropy, etc

92
Q

Why do metallic atoms prefer to arrange themselves in crystal structures?

A

To minimize potential energy, to reduce interatomic distance, and to allow sharing of electrons

93
Q

Which two of the unit cells have close-packed planes (i.e., planes in which the atoms are packed as closely as they possibly can be)?

A

FCC and HCP

94
Q

What does it mean for a material’s atomic structure to be called “amorphous?”

A

The atoms are not arranged in a regular, repeating order. They are randomly arranged (like in a liquid) or almost random.

95
Q

Point defects in crystals involve a single atom in the crystal “lattice.” Which of the following is NOT a point defect?

A

Dislocation

96
Q

If you have a piece of graphite embedded in a diamond, what kind of defect would you call that?

A

Precipitate

97
Q

Most materials are “polycrystalline,” meaning that they are made up of a lot of microscopic crystals aligned randomly. What do we call the interfaces where one microscopic crystal meets another microscopic crystal in a material?

A

Grain boundary

98
Q

Metal example

A

Iron, gold, steel, brass

99
Q

Ceramic example

A

Clay, limestone, glass, concrete

100
Q

Polymer example

A

Rubber, silicone, nylon, teflon, PVC

101
Q

When we say that a diamond is hard, that means

A

It has a high resistance to scratching/indentation

102
Q

Which one typically has a lower elastic modulus, the matrix or reinforcement?

A

Matrix

103
Q

Which one typically has a lower elastic modulus, the matrix or reinforcement?

A

Matrix

104
Q

Which one is typically stronger, the matrix or reinforcement?

A

Reinforcement

105
Q

Which one is typically present as fibers or particles, the matrix or reinforcement?

A

Reinforcement

106
Q

Which component of a concrete composite is present in the greatest volume fraction?

A

Aggregate

107
Q

Why do we use both fine and coarse aggregates together in concrete mixtures?

A

To reduce void spacing and fill volume

108
Q

What factors are considered when restricting the nominal maximum aggregate size to be used in a concrete mixture?

A

Spacing between reinforcement, formwork/minimum dimension, and depth (if it is in a slab)

109
Q

Aggregate moisture content is important to consider in concrete mixture design. Which moisture state
represents the total potential absorption of the aggregate?

A

Saturated surface dry

110
Q

Name a mineral that can be used as a raw material in the production of cement.

A

Limestone, clay, etc.

111
Q

CO2 emissions from cement manufacturing come from:

A

burning of fossil fuels to heat the kiln, power used in grinding and transportation, and decomposition of limestone

112
Q

Which cement hydration reaction product acts as glue, holding all the particles together and providing strength?

A

C-S-H

113
Q

Define segregation in concrete

A

Segregation is the separation of components of the concrete mixture in the fresh or fluid state where aggregates settle to the bottom and cement paste and water rise. It results
in an inhomogeneous mixture

114
Q

Define setting in concrete

A

Setting is the transition from the fluid state to the solid state, after which concrete begins to harden and gain strength.

115
Q

Why does increasing the water-to-cement ratio decrease the compressive strength of concrete?

A

More water-filled pores per volume of concrete

116
Q

Why does increasing age increase the compressive strength of concrete?

A

More C-S-H per volume of concrete

117
Q

When using the volumetric method to design a concrete mixture, what variable in the material proportions is used to help you target the specified 28-day compressive strength?

A

Water-to-cement ratio

118
Q

When using the volumetric method to design a concrete mixture, what variable in the material proportions is used to help you target the specified slump?

A

Water content

119
Q

Tor F? If you oven dry all of your aggregate before batching and mixing concrete, you don’t need to do moisture corrections to your mixture design to adjust the amount of water and aggregate you weigh out.

A

False (you need to correct the water content for the water the aggregate will absorb)

120
Q

In the US, we make cylinders in order to test the compressive strength of concrete. What is the aspect ratio (length/diameter) of the cylinders used?

A

2

121
Q

If we test concrete in compression and capture a stress-vs-strain curve, it appears to be quasi-brittle (i.e. not completely brittle). Why?

A

Cracking creates some permanent deformation

122
Q

We can measure a representation of the tensile strength of concrete using flexural or splitting tensile testing. True or False: The tensile strength of concrete is greater than its compressive strength.

A

False

123
Q

Supplementary cementitious materials (SCMs) are chemically reactive in concrete mixtures by definition. Which of the following is an expected reaction product from the chemical reaction of an SCM?

A

C-S-H

124
Q

Which of the following SCMs is used to make high strength concrete:

A

Silica fume

125
Q

Admixtures are used to manipulate concrete properties. Which chemical would you add to concrete to increase the slump without adding more water?

A

Plasticizer/Superplasticizer

126
Q

How do you prevent plastic shrinkage cracking?

A

Moist curing

127
Q

Which of the following is used to prevent cracking from freeze-thaw cycles?

A

Air-entraining admixtures

128
Q

Why does corrosion of steel reinforcement in concrete cause cracking?

A

The rust that forms is expansive

129
Q

Why are hydrocarbons with 1000 carbons in a molecule solid state at room T while hydrocarbons with 4 carbons in a molecule in the gas state?

A

It has more H bonds

130
Q

Why does polystyrene (PS) have a higher yield strength and lower ductility than polyethylene (PE)?

A

PS has bulkier functional groups

131
Q

Which fiber material would give you the highest elastic modulus in an FRP composite made with an epoxy resin?

A

Carbon

132
Q

In which of the following civil engineering applications do we use FRP composites?

A

Repair and strengthening of concrete structural elements

133
Q

Asphalt binder (or bitumen) is considered to be a polymer. Why?

A

It has a glass transition temperature (brittle when cold), contains hydrocarbon molecules that have a high molecular weight, and it melts when heated bc of H bonds breaking

134
Q

In which direction is the strength of wood the highest?

A

Compression parallel to the grain

135
Q

In which of the following moisture states is wood at its highest volume assuming that the fiber saturation point is 26%

A

100% and 50% moisture

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