Exam 1 Flashcards
(160 cards)
1
Q
Investigate relationships between structures and properties of materials
Design/develop new materials
A
Materials science
2
Q
Create products from existing materials
Develop materials processing techniques
A
Materials engineering
3
Q
Processing affects _______ and ________ affects ________
A
Structure
Structure
Hardness
4
Q
Properties of Metals?
A
Strong, ductile
High thermal & electrical conductivities
Opaque, reflective
5
Q
Properties of Polymers/plastics?
A
compounds of non-metallic elements
Soft, ductile, low strengths, low densities
Low thermal & electrical conductivities
Opaque, translucent or transparent
6
Q
Properties of Ceramics?
A
compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides)
Hard, Brittle
Low thermal & electrical conductivities
Opaque, translucent, or transparent
7
Q
Understand Material Selection Procedure
A
**Screenshot of slide
8
Q
What are the six properties of materials?
A
Mechanical Electrical Thermal Magnetic Optical Deteriorative
9
Q
Increasing ______ increases _____ of steel.
A
carbon content
hardness
10
Q
What 3 things increase resistivity?
A
Increasing temperature
Increasing impurity content
Deformation
11
Q
What is Thermal Conductivity ?
A
measure of a material’s ability to conduct heat
12
Q
Increasing impurity content decreases _________.
A
Thermal conductivity
13
Q
Highly porous materials are _____ conductors of heat: therefore ceramics have _____ thermal conductivity
A
poor
ceramics
14
Q
What are two Magnetic properties?
A
Magnetic storage and magnetic permeability
15
Q
The _________ of some materials depend on their structural characteristics
A
light transmittance
16
Q
What is an example of a deteriorative property?
A
stress-corrosion cracking
• For stress-corrosion cracking, rate of crack growth is diminished by heat treating
17
Q
Materials’ properties depend on their _______; ________ are determined by how materials are processed
A
structure(s)
18
Q
In terms of chemistry the three classifications of materials are
A
metals, ceramics, and polymers
19
Q
An important role of engineers is that of _________
A
materials selection
20
Q
Organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements low density and may be extremely flexible
A
Polymers
21
Q
combination of metallic elements (free electrons)
good conductors of electricity and heat
not transparent to visible light
strong and ductile
A
Metals
22
Q
Compounds between metallic and nonmetallic elements, such as nitrides, oxides, carbides
insulators of electricity and heat
resistant to high temperature and harsh environment
A
Ceramics
23
Q
Consisting of more than one material type, combination of the best characteristics of each of the component materials
A
Composities
ex. fiberglass
24
Q
the smallest particle of an element that possesses the physical and chemical properties of that element
A
atom
25
Each chemical element is characterized by the number of protons in the nucleus, or the
atomic number
26
For an electrically neutral (equilibrium state) or complete atom: Atomic number =________
number of protons
27
Atomic mass =
mass of protons + mass of neutrons
28
the electrons that occupy the outermost filled shell
Valence electrons
29
Know atomic chem review
**lecture 2a
30
Smaller electronegativity is on the _____ side of the periodic table, while larger is on the _______
left
| right
31
When is atomic bonding achieved?
when the atoms fill their outer s and p shells
32
What are the 3 types of atomic bonding?
Ionic Bonding
Covalent Bonding
Metallic Bonding
33
What is a type of secondary bonding?
van der Waals (weak bonding)
34
What is an ion?
an atom, or a molecule, in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge.
35
What does ionic bonding occur between?
metallic and nonmetallic elements which are situated at the horizontal extremities of the periodic table
36
What occurs during ionic bonding?
Metallic elements “transfer” valence electrons to nonmetallic atoms They become ions
-all the atoms acquire stable or inert gas configurations.
37
The predominant bonding in _______ is ionic.
ceramics
38
Ionic materials are _____ and ______
hard
| brittle
39
What occurs during covalent bonding?
Stable electron configurations are assumed by the “sharing” of electrons between adjacent atoms.
40
The predominant bonding in _______ is covalent.
polymers
41
Covalent bonds may be very ____, or may be very ____
strong
| weak
42
What occurs during metallic bonding?
The valence electrons are not bound to any particular atom in the solid and are free to drift throughout the entire metal.
43
Characteristics & Caveats of metallic bonding?
Bonding may be strong or weak.
Good ductility
Good electrical conductivity
44
Why are metallic materials usually good conductors?
Because their electrons are free to move in the sea of electrons
45
weak electrostatic attractions between atomic or molecular dipoles
Van der Waals
46
________ bonds can change dramatically the properties of certain materials.
Van der Waals
47
Melting Temperature (Tm) is ____ if the bond energy is _____
larger
48
Elastic Modulus E (measure of a material)
| E is ______ if the bond energy is ______
larger
49
Know the summary of bonding slide
**screenshot of slide
50
What is the summary of the material selection process?
Application ---> Require Properties -----> Candidate Materials ------> Processing Techniques -----> Structure -----> Property -----> Performance
51
The properties of some materials are directly related to their __________
crystal structures
52
How do atoms align themselves in a crystalline materials?
in a repetitive, precise 3-dimensional patterns over large atomic distances
53
Lattice
a three-dimensional array of points coinciding with atom positions
54
Unit cell
a smallest subdivision (repetitive) of crystalline lattice. Still retains overall characteristics of entire lattice
55
Hard sphere model
Atoms are thought of as being solid spheres having well-defined diameters; the spheres representing nearest-neighbor atoms touch one another
56
Face-Centered Cubic (FCC) Crystal Structure
A unit cell of cubic geometry with atoms located at each of the corners and the centers of all the cube faces
57
Number of Atoms in FCC Unit Cell
4
58
Body-Centered Cubic (BCC) Crystal Structure
A unit cell of cubic geometry with atoms located at all eight corners and a single atom at the cube center
59
Number of Atoms in BCC Unit Cell
2
60
What has important effect upon material properties?
Structure
61
some chemical elements to exist in two or more different forms, in the same physical state
Allotropic
62
theoretical density of the material
Density of a unit cell
63
Theoretical density is usually within ______ of the actual density of the pure material.
2 percent
64
Most efficient form of packing is the _________
close packed layer
65
Less efficient is _______
square packing
66
Materials that have _______ structures deform more easily than do body-centered cubic materials that are not ______
close packed
67
Materials that are _______ tend to have higher strength values and are harder to deform than ________ materials
not close packed
| close packed
68
_______ materials have the most slip systems and thus are the easiest to deform without fracture
FCC - Face centered cubic
69
For FCC, Close packed directions are ____ diagonals.
face
70
For BCC, Close packed directions are ____ diagonals
cube
71
Number of atoms/ unit cell in HCP
6
72
Some materials have more than one crystal structure, depending on _______ & _______
temperature
| pressure
73
Allotropic Materials
materials that change crystal structure depending on temperature
74
Upon completion of solidification, the colonies contact each other, forming ________
Grain boundaries
75
Metals deform more easily in directions along which __________ on planes of atoms that are ________ together
atoms are in closest contact
| most tightly packed
76
Know how to find miller indices
**Screenshot of slide
77
Mechanical properties
response of the material to an applied force or stress
78
Important mechanical properties are
strength, ductility, stiffness, and hardness
79
Three principal ways in which a load may be applied
Tension(tensile test)
Compression(compression test)
Shear (shear test)
80
Lateral strains are _______ when the force is in tension
negative
81
_____ is always dimensionless
Strain
82
a linear portion on the stress-strain curve and the material will return to its original shape upon unloading
Elastic Region
83
in elastic region, stress-strain are proportional to each other
Hooke’s law
84
The ratio of the lateral and axial strains
Poisson’s Ratio
85
Larger _______ minimize elastic deflection
elastic moduli
86
What’s going on during elastic deformation?
Bond stretching during elastic deformation!
87
Elastic means _________ and __________
Elastic
| Nonpermanent
88
modulus of elasticity is
a measure of stiffness of the material
89
Plastic Behavior
As the material is deformed beyond the yield strength point, permanent, or plastic deformation occurs
90
yield strength (proportional limit)
the initial departure from linearity of the stress-strain curve
91
What’s going on during plastic deformation?
Dislocation is moving during plastic deformation
92
Plastic deformation, or dislocation movement is __________
permanent
93
Yield Strength
Stress at which noticeable plastic deformation has
| occurred
94
Tensile Strength
Maximum possible engineering stress in tension
95
When does tensile strength for metals occur?
when noticeable necking starts
96
Ductility
is the ability of a material to bend, stretch, or distort without breaking
97
plastic tensile strain at fracture
Percent Elongation (%PE)
98
A ductile material is ________
flexible
99
Brittle materials:
| %EL
< 5%
100
Ductile materials:
| %EL
> 5%
101
Toughness
The ability of a material to absorb energy up to fracture
102
For a material to be tough
| it must display both _______ & _______
strength
| ductility
103
This reversible behavior often shows a linear relation between stress and strain
Elastic behavior
104
This permanent deformation
Plastic behavior
105
the slope of the elastic portion
Young’s modulus
106
the stress at fracture
Fracture strength
107
The total energy absorbed during plastic deformation…. to break the material
Toughness
108
The plastic strain at failure
Ductility
109
Hardness
A measurement of a material’s resistance to penetration or localized plastic deformation
110
Steps in hardness test
A small indenter is forced into the surface of a material to be tested with certain load.
The depth / size of the resulting indentation is measured.
Such data are converted to a hardness number
111
The softer the material, the ______ and ______ the indentation, and the _____ the hardness number
larger
deeper
lower
112
What are hardness tests are performed more frequently than any other mechanical tests?
Simple / inexpensive
nondestructive
Other mechanical properties may be estimated from hardness data
113
_________ is an accurate hardness measurement for soft materials
Brinell hardness (HB)
114
________ is the most widely used of all metal hardness testing methods
Rockwell hardness (HR)
115
_____ iron is much harder than the cast iron.
gray
116
Atomic vibrations are in the form of _______ or _______
lattice waves
| phonons
117
Thermal Expansion (α )
Materials change size when temperature is changed
118
Polymers have larger α values because of ___________
weak secondary bonds
119
Thermal Conductivity
The ability of a material to transport heat.
120
Atomic vibrations and free electrons in hotter regions transport energy to cooler regions.
Atomic perspective
121
Why does thermal stress occur?
restrained thermal expansion/contraction
| temperature gradients that lead to differential dimensional changes
122
The thermal properties of materials include:
Coefficient of thermal expansion
| Thermal conductivity
123
Coefficient of thermal expansion
the size of a material changes with a change in temperature
| polymers have the largest values
124
Thermal conductivity
the ability of a material to transport heat
| metals have the largest values
125
Plastic deformation is __________ deformation.
permanent (non-recoverable)
126
_________ and _________ are measures of a material’s resistance to plastic deformation
Strength
| hardness
127
During the plastic deformation, __________ must be ruptured and then reformed
interatomic bonds
128
In crystalline solids, plastic deformation most often involves the ___________
motion of dislocations
129
Edge Dislocation
associated with the edge of the extra half plane of atoms
130
Breaking the bonds together to _________ requires extremely large stress
facilitate slip
131
For metals, plastic deformation occurs by ______
slip – an edge dislocation slides over adjacent plane half-planes of atoms
132
A dislocation moves along a _______ in a _________ perpendicular to the dislocation line
slip plane
| slip direction
133
The slip direction is the same as the ________ direction
Burgers vector
134
Slip plane
plane on which easiest slippage occurs
| Highest planar densities
135
Slip directions
- directions of movement
| Highest linear densities
136
BCC and FCC metals have a relatively ______ number of slip systems
large
| Relatively ductile
137
HCP metals having _____ active slip systems
few
| Relatively brittle
138
Dislocation Motion
Produces plastic deformation
Depends on incrementally breaking
bonds
139
During plastic deformation, the number of dislocations ________ dramatically.
increases
140
the separation of a body into two or more pieces in response to a static stress
simple fracture
141
Two general types of fracture
ductile
| brittle
142
ductile
Slow crack propagation
Accompanied by significant plastic deformation
Fails with warning
143
brittle
Rapid crack propagation
Little or no plastic deformation
Fails without warning
144
______ fracture generally more desirable than _______ fracture
Ductile
| Brittle
145
cup-and-cone fracture
moderately ductile
146
flat surfaces
brittle fracture
147
one piece
| large deformation
Ductile fracture
148
many pieces
| small deformations
Brittle fracture
149
What are the stages of Stages of Moderately Ductile Failure?
```
necking
void nucleation
void growth and coalescence
crack propagation
fracture
```
150
_____ fracture surface displays V-shaped, chevron markings
Brittle
151
V features point to the
crack initiation site
152
Transgranular crack propagation
through grains
153
Intergranular crack propagation
between grains
154
What are the Principles of Fracture Mechanics?
Fracture occurs as result of crack propagation
| Measured fracture strengths of most materials much lower than predicted by theory
155
Why are measured fracture strengths of most materials much lower than predicted by theory?
```
microscopic flaws (cracks) always exist in materials
magnitude of applied tensile stress amplified at the tips of these cracks
```
156
_____ are Stress Concentrators
flaws
157
Stress concentration ______ for sharp cracks—propagate at _____ stresses than cracks with blunt tips
higher
| lower
158
Crack propagation for ductile materials ______
plastic deformation at crack tip when stress reaches yield strength—tip blunted—lowers stress conc.
159
Measure of material’s resistance to brittle fracture when a crack is present
Fracture Toughness
160
How to Reducing Stress Concentration ?
General Techniques
1. Increase Fillet Radius (R)
2. Reduce W/H ratio
