Mats. Final Flashcards
(135 cards)
1
Q
Graphite, iron, quartz
A
Crystalline
2
Q
BCC
A
Bold
3
Q
Glass
A
Amorphous
4
Q
oooooooo
oooooAooo
oooooooo
ooooobooo
A
A = Vacancy
b = substitution
5
Q
Graphite in cast iron is an example of what type of defect?
A
precipitae
6
Q
Dislocation definition
A
extra half plane of atoms
7
Q
how are grain boundaries formed in crystals?
A
cooling from a liquid
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”
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
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
11
Q
when we say that planes of atoms are slipping, what’s actually moving?
A
dislocations
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
13
Q
T or F: Mechanisms used to make metals stronger also make them more brittle.
A
T
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
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
16
Q
what’s special about the microstructure that forms after a eutectic or eutectoid transformation?
A
it’s layered
17
Q
what’s the melting temperature of pure iron?
A
1538 C
18
Q
T or F: Austenite is a liquid
A
F but a FCC
19
Q
What is the yield strength of a mild 1018/A36 steel?
A
36 ksi
20
Q
Stress concentrations at crack tips are dependent on:
A
Crack length, Crack radius of curvature, Applied tensile stress
21
Q
Name one factor that the stress intensity (KI) depends on
A
crack length, applied tensile stress, geometry
22
Q
What happens to atoms in plastic deformation? (ductile)
A
planes of atoms “slip” in shear
23
Q
Ductile materials have 2 components:
A
CPP and dislocations
24
Q
How do dislocations exist?
A
Entropy
25
Dislocation motion?
visualize car driving down road as shear stress needed to move dislocation
26
Why is deformation important ?
Once broken & reformed a new bond, you would have to break it again to go backward
27
Why does slip happen only on close (or closely) packed planes?
CPP have shortest slip distance (break fewest bonds) "slip planes"
28
Step Process of Slip Planes
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
29
HCP brittle or ductile than rest?
Brittle
30
Alloying?
dissolving an impurity metal into majority metal
31
strengthening = hardening =
embrittling
32
Fe3C (cemenite) is ductile or brittle?
brittle
33
Smaller grain size =
more brittle (stronger) and cool faster
34
weakening = softening =
ductilifying
35
Component?
composition which is ingredients
36
phase?
structure which is how components are arranged in space
37
What's ferrite?
alpha iron: BCC
38
Pearlite?
thinner the layers the faster you cool it and less time for diffusion
39
As C content increases...
strength increases, ductility decreases, and weldability decreases
40
43xx means...
nickel, cr, and maybe molybdenum
41
How does ductile mats. fail?
in yielding. when dislocations move along CPP due to resolved shear stress
42
How do brittle mats. fail?
in tension due to crack growth
43
Fracture when
Applied stress greater than or equal to stress bond break
44
Crack will grow when
max stress greater than or equal to stress bond break
45
fracture toughness =
KIC (stress = applied stress needed for cracks to start growing
46
Creep =
constant stress (strain reduces)
47
stress relaxation =
constant strain (stress reduces)
48
Fatigue =
cyclical load which is worried about tension
49
the longer the cracks...
the longer the stress concentration
50
fatigue limit can...
withstand infinite N, as long as S < fatigue limit
51
N is highly variable and...
dependent on flaws - change with specimens
52
Tresca
ductile mats. = max shear stress
53
Rankine
brittle mats. = max principal stress theory
54
Galvanic Couple
anode oxides and cathode reduces and get a voltage
55
Corrosive environments include
moisture containing dissolved O
Sulfur (acid rain)
NaCl (sea water)
Soil (damp)
56
Types of corrosion
Uniform attack, galvanic corrosion (2 alloys/metals are electrically coupled), crevice and pitting, intergranular, stress corrosion, and H embrittlement in steel
57
Corrosion Prevention
Paint, "passivation" (protective oxide barrier)
58
Which of the following is an example of a material that has been strengthened using precipitation hardening?
Steel
59
Why does making a metal stronger also make it more brittle?
Dislocations can't move easily.
60
Why are ductile mats. less crack sensitive than brittle mats.?
Plastic deformation at the crack tip increases the radius of curvature
61
Why did zinc and copper pennies behave differently when hit by a hammer?
Some slip planes are inactive at cold temps
62
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?
Tensile stress make cracks grow
63
Why does the oxidation of silver or aluminum not cause extensive damage while the oxidation of steel does cause extensive damage?
Steels oxidation product flakes off and exposes new surface
64
In galvanized steel, the steel is coated with
Zinc
65
Why doesn’t steel reinforcement in concrete start rusting immediately after placement since concrete
contains water with dissolved ions?
The high pH of concrete pore solution prevents steel from forming rust
66
Covalent Bond
A chemical bond involving the sharing of electron pairs between atoms is known as a covalent bond (H20, N2, CH4, H2, O2)
67
Ionic Bond
the complete transfer of valence electron(s) between atoms (NaCl, NaBr, KF, KCl)
68
Metallic Bond
Same chemicals mixed (Gold, Silver, Copper)
69
Hydrogen Bond
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
Why are the bonding energy and melting temperature linearly correlated for metals?
Because melting occurs when metallic bonds in metals are broken
71
Bonds that share valence electrons?
Covalent and Metallic
72
Bonds that have electrostatic attraction?
Ionic and Hydrogen
73
When thermoplastic polymers melt...
H bonds between hydrocarbon chains break
74
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?
PE has more H bonds than propane
75
Highest to Lowest most expected plastic deformation polymers?
Polyethylene, polystyrene, rubber
76
Why is rubber elastic?
It has covalently-bonded cross-links between hydrocarbon chains
77
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)?
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
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?
Steel
79
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?
FRP does not corrode/rust
80
In the FRP composites used in civil engineering, the fibers are:
Continuous through the material and aligned in parallel to each other
81
In the FRP composites used in civil engineering, the matrix is
Epoxy/resin
82
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?
Around the circumference of the column (transverse)
83
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
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
Asphalt flows like a liquid at high temperatures and is a solid at room temperature because
It is a polymer, and the hydrogen bonds between chains break at high temperatures
85
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?
rutting
86
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?
The behavior of the asphalt under the expected traffic loads
87
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.)
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
Wood is a natural composite material made of polymer fibers with a polymer matrix. What polymer are the fibers made from?
Cellulose
89
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%.
1) Highest 50% = 30% > 20% > 10% (4) Lowest
90
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.
10%
91
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
Size, defects, anisotropy, etc
92
Why do metallic atoms prefer to arrange themselves in crystal structures?
To minimize potential energy, to reduce interatomic distance, and to allow sharing of electrons
93
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)?
FCC and HCP
94
What does it mean for a material’s atomic structure to be called “amorphous?"
The atoms are not arranged in a regular, repeating order. They are randomly arranged (like in a liquid) or almost random.
95
Point defects in crystals involve a single atom in the crystal “lattice.” Which of the following is NOT a point defect?
Dislocation
96
If you have a piece of graphite embedded in a diamond, what kind of defect would you call that?
Precipitate
97
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?
Grain boundary
98
Metal example
Iron, gold, steel, brass
99
Ceramic example
Clay, limestone, glass, concrete
100
Polymer example
Rubber, silicone, nylon, teflon, PVC
101
When we say that a diamond is hard, that means
It has a high resistance to scratching/indentation
102
Which one typically has a lower elastic modulus, the matrix or reinforcement?
Matrix
103
Which one typically has a lower elastic modulus, the matrix or reinforcement?
Matrix
104
Which one is typically stronger, the matrix or reinforcement?
Reinforcement
105
Which one is typically present as fibers or particles, the matrix or reinforcement?
Reinforcement
106
Which component of a concrete composite is present in the greatest volume fraction?
Aggregate
107
Why do we use both fine and coarse aggregates together in concrete mixtures?
To reduce void spacing and fill volume
108
What factors are considered when restricting the nominal maximum aggregate size to be used in a concrete mixture?
Spacing between reinforcement, formwork/minimum dimension, and depth (if it is in a slab)
109
Aggregate moisture content is important to consider in concrete mixture design. Which moisture state
represents the total potential absorption of the aggregate?
Saturated surface dry
110
Name a mineral that can be used as a raw material in the production of cement.
Limestone, clay, etc.
111
CO2 emissions from cement manufacturing come from:
burning of fossil fuels to heat the kiln, power used in grinding and transportation, and decomposition of limestone
112
Which cement hydration reaction product acts as glue, holding all the particles together and providing strength?
C-S-H
113
Define segregation in concrete
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
Define setting in concrete
Setting is the transition from the fluid state to the solid state, after which concrete begins to harden and gain strength.
115
Why does increasing the water-to-cement ratio decrease the compressive strength of concrete?
More water-filled pores per volume of concrete
116
Why does increasing age increase the compressive strength of concrete?
More C-S-H per volume of concrete
117
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?
Water-to-cement ratio
118
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?
Water content
119
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.
False (you need to correct the water content for the water the aggregate will absorb)
120
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?
2
121
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?
Cracking creates some permanent deformation
122
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.
False
123
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?
C-S-H
124
Which of the following SCMs is used to make high strength concrete:
Silica fume
125
Admixtures are used to manipulate concrete properties. Which chemical would you add to concrete to increase the slump without adding more water?
Plasticizer/Superplasticizer
126
How do you prevent plastic shrinkage cracking?
Moist curing
127
Which of the following is used to prevent cracking from freeze-thaw cycles?
Air-entraining admixtures
128
Why does corrosion of steel reinforcement in concrete cause cracking?
The rust that forms is expansive
129
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?
It has more H bonds
130
Why does polystyrene (PS) have a higher yield strength and lower ductility than polyethylene (PE)?
PS has bulkier functional groups
131
Which fiber material would give you the highest elastic modulus in an FRP composite made with an epoxy resin?
Carbon
132
In which of the following civil engineering applications do we use FRP composites?
Repair and strengthening of concrete structural elements
133
Asphalt binder (or bitumen) is considered to be a polymer. Why?
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
In which direction is the strength of wood the highest?
Compression parallel to the grain
135
In which of the following moisture states is wood at its highest volume assuming that the fiber saturation point is 26%
100% and 50% moisture
