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Materials > Exam 1 > Flashcards

Exam 1 Flashcards

1
Q

How large is a subatomic structure?

A

<1A

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2
Q

How large is an atomic structure?

A

1A

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3
Q

How large is a microstructure?

A

nm to mm

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4
Q

How large is a macrostructure?

A

> 1mm

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5
Q

What are the 5 types of materials?

A

Metals, ceramics, polymers, composites, advanced materials

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6
Q

What is an alloy?

A

Mixture of two or more elements

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7
Q

What is unique about metals and electrons?

A

Large number of nonlocalized electrons

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8
Q

What is ductility?

A

Measure of materials ability to undergo plastic deformation before fracture

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9
Q

Ceramics are a compound of what?

A

Metallic and non-metallic elements

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10
Q

Optically, ceramics may be?

A

Transparent, translucent, or opaque

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11
Q

Polymers are?

A

Organic compounds that are chemically based on C H, and non-metallic elements

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12
Q

Polymers have _ molecular weight?

A

High

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13
Q

Polymers are what in regards to density and ductility?

A
  • Low density

- Extremely ductile

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14
Q

What is a composite?

A

2+ individual materials

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15
Q

What are material property charts?

A

Two material properties plotted against each other

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16
Q

What are the 4 different types of advanced materials?

A

Semiconductors, biomaterials, smart materials, nanomaterials

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17
Q

What are nano-materials?

A

10-100nm

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18
Q

What is affected when you reduce the size of a material?

A

Optical properties

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19
Q

What are the 4 ways to apply load?

A

Tension, compression, shear, torsional

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20
Q

Explain tension tests

A
  • Destructive test that measures stress and strain as a function of time
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21
Q

What are the equations for stress and strain with a tension test?

A 
Stress = F/A
Strain = delta l/lo
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22
Q

What are the equations for shear stress and strain?

A 
Stress = F/A
Strain = tan theta = delta x/y
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23
Q

During torsional tests, what does phi mean?

A

Angle of twist

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24
Q

What are the equations for tensile stress and shear stress for a torsional test?

A

T Stress = σ (1+cos 2theta/2)

S Stress = σ (sin2theta/2)

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25
Q

Explain hooke’s law

A

σ = E * e

Tensile stress = modulus of elasticity * strain

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26
Q

What is the modulus of elasticity?

A

Stiffness or resistance to elastic deformation

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27
Q

Explain the stress-strain diagram

A

σ vs e, slope = E

Shows elastic deformation

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28
Q

What is elastic deformation?

A

Stress and strain are linearly proportional

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29
Q

Where is the elastic portion of the stress-strain curve?

A

When the curve isn’t linear

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30
Q

What is elastic strain?

A

Small changes in interatomic spacing

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31
Q

What is the relationship between the temperature and modulus of elasticity?

A

As T goes up, E goes down

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32
Q

What is the relationship between shear stress and shear strain

A

τ = G *γ

shear stress= shear modulus * shear strain

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33
Q

What is anelasticity?

A

Time dependent elastic behavior

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34
Q

What is anelastic behavior called for polymers?

A

Viscoelastic behavior

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35
Q

Explain poisson’s ratio

A

v = negative ration of transverse and longitudinal strains

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36
Q

What is the modulus of elasticity for isotropic materials?

A

E = 2G (1+v)

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37
Q

For anisotropic materials, what does the modulus of elasticity depend on?

A

Crystallographic direction

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38
Q

What is happening during plastic deformation?

A

Bonds break and form

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39
Q

Elastic deformation is _ and plastic deformation is _

A

Nonpermanent, permanent

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40
Q

What is yield strength (σy)

A

Measure of resistance to plastic deformation

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41
Q

What is tensile strength?

A

Max stress that can be sustained in tension

42
Q

What is the yield strength associated with?

A

Lower yield point

43
Q

What are the two measure of ductility?

A

% Elongation and % Area Reduction

44
Q

What is resilience?

A

Capacity of a material to absorb energy when deformed elastically and recovered (Ur)

45
Q

What is the relationship between stress and the modulus of elasticity in regards to resilient materials?

A

When stress is high, E is low

46
Q

What is toughness?

A

Materials resistance to fracture when there’s a crack

Ability of a material to absorb energy and plastically deform before fracturing

47
Q

What are the equations for true stress and strain?

A 
σt = F/Ai
et = ln(li/lo)
48
Q

What is hardness?

A

Material’s resistance to localized plastic deformation

49
Q

Yielding occurs when?

A

Onset of plastic deformation

50
Q

How do you calculate the average atomic weight of an element?

A

A = sum( fi*Ai)
fi - fraction of occurrence of isotope
Ai - atomic weight

51
Q

Explain the Bohr atomic model

A

Different orbitals/energy levels for electrons. Going to a higher level = absorption of energy
Going to lower level = emission of energy

52
Q

What are quantized electrons?

A

Electrons permitted to have only specific values of energy

53
Q

Explain the wave-mechanical model of atoms

A

The electron is both a wave and particle, position is a probability of being at various locations around the nucleus

54
Q

What do quantum numbers describe?

A

Shape, size, orientation of an electron

55
Q

What is the Pauli exclusion principle?

A

Each electron state has no more than 2 electrons, having opposite spins

56
Q

Electropositive elements want to do what with electrons?

A

Give them up

57
Q

As you go up and right of the periodic table, how does electronegativity change?

A

Increases

58
Q

What is the relationship between bonding energy and melting temperature?

A

Large bonding = High melting

59
Q

What are the three types of bonds?

A

Ionic, covalent, metallic

60
Q

What does an electron cloud look like?

A

Ion cores with valence electrons in between so positive cores don’t repel each other

61
Q

Van der Wall bonding occurs between?

A

Dipoles

62
Q

We can find % ionic character when?

A

We have covalent-ionic mixed bonding

63
Q

What is the relationship between bond energy and melting temp?

A

Larger Eo, higher Tm

64
Q

Relate bond energy, melting temp, modulus of elasticity, and coefficient of thermal expansion to ceramics

A

Large, high, large, small

65
Q

Relate bond energy, melting temp, modulus of elasticity, and coefficient of thermal expansion to metals

A

Variable, moderate, moderate, moderate

66
Q

Relate bond energy, melting temp, modulus of elasticity, and coefficient of thermal expansion to polymers

A

Weak between chains, low, small, large

67
Q

Van der Wall bonds are _ than primary bonds

A

Weaker

68
Q

What are the two classes of structures when materials solidify?

A

Glassy/amorphous/noncrystalline , crystalline

69
Q

Why is atomic packing dense for metals?

A

Since it’s non-directional there’s minimal restriction on the number and position of neighbor atoms. Additionally, there’s a high degree of shielding of ion cores

70
Q

What are the 4 types of metallic crystal structures?

A

SC, FCC, BCC, HCP

71
Q

What is the coordination number?

A

Number of nearest-neighbor atoms

72
Q

What is the atomic packing factor?

A

Vol of atoms in unit cell/ Vol of cell

73
Q

What is the coordination number for SC?

A

6

74
Q

How to find the vol of atoms in a unit cell?

A

atoms N * vol of atom

75
Q

What is the coordination number for FCC?

A

12

76
Q

What is the coordination number for BCC?

A

8

77
Q

What is the coordination number for HCP?

A

12

78
Q

Equation for density?

A 
nA / VcNa
# atoms per unit cell * atomic weight/ Vol unit cell * avagadro's number
79
Q

Rank the densities of metals, ceramics, and polymers

A

Metal> ceramic> polymer

80
Q

What is polymorphism?

A

Material has more than one crystal structure

81
Q

Allotropy is polymorphism in?

A

Elemental solids

82
Q

Equivalent crytallographic directions are called?

A

Families

83
Q

What is planar density?

A

atoms centered on a plane/Area of plane

84
Q

What is the packing sequence for HCP?

A

ABAB

85
Q

What is the packing sequence for FCC?

A

ABCABC

86
Q

What is anisotropy?

A

Physical properties dependent on the crystallographic direction

87
Q

What are grain boundaries?

A

Boundary region separating two grains with atomic mismatch

88
Q

What is X-ray diffraction?

A

Technique used for determination of crystal structures

89
Q

When does diffraction occur?

A

Wave encounters regularly spaced obstacles

90
Q

During constructive interference, amplitudes are?

A

Added

91
Q

During destructive interference, amplitudes?

A

Cancel

92
Q

As crystal symmetry decreases, XRD peaks?

A

Increase

93
Q

Peak positions are determined by?

A

Size, shape of unit cell

94
Q

Peak intensities are determined by?

A

Atomic number and position of atoms

95
Q

Peak widths are determined by?

A

Instruments, temp, crystal size, strain, imperfections

96
Q

Amorphous structures are due to?

A

Rapid cooling

97
Q

What are the 7 crystal systems?

A

Cubic, tetragonal, hexagonal, orthorhomic, rhombohedral, monoclinic, and triclinic

98
Q

Single crystals are?

A

Atomic order extends uninterrupted over the entirety of the specimen

99
Q

For isotropic materials, properties are?

A

Independent of the direction

100
Q

Noncrystalline materials lack?

A

Systematic and regular arrangement

101
Q

Noncrystaliine materials are also called?

A

Amorphous

Materials (12 decks)

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