Exam 1 Flashcards
Investigate relationships between structures and properties of materials
Design/develop new materials
Materials science
Create products from existing materials
Develop materials processing techniques
Materials engineering
Processing affects _______ and ________ affects ________
Structure
Structure
Hardness
Properties of Metals?
Strong, ductile
High thermal & electrical conductivities
Opaque, reflective
Properties of Polymers/plastics?
compounds of non-metallic elements
Soft, ductile, low strengths, low densities
Low thermal & electrical conductivities
Opaque, translucent or transparent
Properties of Ceramics?
compounds of metallic & non-metallic elements (oxides, carbides, nitrides, sulfides)
Hard, Brittle
Low thermal & electrical conductivities
Opaque, translucent, or transparent
Understand Material Selection Procedure
**Screenshot of slide
What are the six properties of materials?
Mechanical Electrical Thermal Magnetic Optical Deteriorative
Increasing ______ increases _____ of steel.
carbon content
hardness
What 3 things increase resistivity?
Increasing temperature
Increasing impurity content
Deformation
What is Thermal Conductivity ?
measure of a material’s ability to conduct heat
Increasing impurity content decreases _________.
Thermal conductivity
Highly porous materials are _____ conductors of heat: therefore ceramics have _____ thermal conductivity
poor
ceramics
What are two Magnetic properties?
Magnetic storage and magnetic permeability
The _________ of some materials depend on their structural characteristics
light transmittance
What is an example of a deteriorative property?
stress-corrosion cracking
• For stress-corrosion cracking, rate of crack growth is diminished by heat treating
Materials’ properties depend on their _______; ________ are determined by how materials are processed
structure(s)
In terms of chemistry the three classifications of materials are
metals, ceramics, and polymers
An important role of engineers is that of _________
materials selection
Organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements low density and may be extremely flexible
Polymers
combination of metallic elements (free electrons)
good conductors of electricity and heat
not transparent to visible light
strong and ductile
Metals
Compounds between metallic and nonmetallic elements, such as nitrides, oxides, carbides
insulators of electricity and heat
resistant to high temperature and harsh environment
Ceramics
Consisting of more than one material type, combination of the best characteristics of each of the component materials
Composities
ex. fiberglass
the smallest particle of an element that possesses the physical and chemical properties of that element
atom
Each chemical element is characterized by the number of protons in the nucleus, or the
atomic number
For an electrically neutral (equilibrium state) or complete atom: Atomic number =________
number of protons
Atomic mass =
mass of protons + mass of neutrons
the electrons that occupy the outermost filled shell
Valence electrons
Know atomic chem review
**lecture 2a
Smaller electronegativity is on the _____ side of the periodic table, while larger is on the _______
left
right
When is atomic bonding achieved?
when the atoms fill their outer s and p shells
What are the 3 types of atomic bonding?
Ionic Bonding
Covalent Bonding
Metallic Bonding
What is a type of secondary bonding?
van der Waals (weak bonding)
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.
What does ionic bonding occur between?
metallic and nonmetallic elements which are situated at the horizontal extremities of the periodic table
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.
The predominant bonding in _______ is ionic.
ceramics
Ionic materials are _____ and ______
hard
brittle
What occurs during covalent bonding?
Stable electron configurations are assumed by the “sharing” of electrons between adjacent atoms.
The predominant bonding in _______ is covalent.
polymers
Covalent bonds may be very ____, or may be very ____
strong
weak
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.
Characteristics & Caveats of metallic bonding?
Bonding may be strong or weak.
Good ductility
Good electrical conductivity
Why are metallic materials usually good conductors?
Because their electrons are free to move in the sea of electrons
weak electrostatic attractions between atomic or molecular dipoles
Van der Waals
________ bonds can change dramatically the properties of certain materials.
Van der Waals
Melting Temperature (Tm) is ____ if the bond energy is _____
larger
Elastic Modulus E (measure of a material)
E is ______ if the bond energy is ______
larger
Know the summary of bonding slide
**screenshot of slide
What is the summary of the material selection process?
Application —> Require Properties —–> Candidate Materials ——> Processing Techniques —–> Structure —–> Property —–> Performance
The properties of some materials are directly related to their __________
crystal structures
How do atoms align themselves in a crystalline materials?
in a repetitive, precise 3-dimensional patterns over large atomic distances
Lattice
a three-dimensional array of points coinciding with atom positions
Unit cell
a smallest subdivision (repetitive) of crystalline lattice. Still retains overall characteristics of entire lattice
Hard sphere model
Atoms are thought of as being solid spheres having well-defined diameters; the spheres representing nearest-neighbor atoms touch one another
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
Number of Atoms in FCC Unit Cell
4
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
Number of Atoms in BCC Unit Cell
2
What has important effect upon material properties?
Structure
some chemical elements to exist in two or more different forms, in the same physical state
Allotropic
theoretical density of the material
Density of a unit cell
Theoretical density is usually within ______ of the actual density of the pure material.
2 percent
Most efficient form of packing is the _________
close packed layer
Less efficient is _______
square packing
Materials that have _______ structures deform more easily than do body-centered cubic materials that are not ______
close packed
Materials that are _______ tend to have higher strength values and are harder to deform than ________ materials
not close packed
close packed
_______ materials have the most slip systems and thus are the easiest to deform without fracture
FCC - Face centered cubic
For FCC, Close packed directions are ____ diagonals.
face
For BCC, Close packed directions are ____ diagonals
cube
Number of atoms/ unit cell in HCP
6
Some materials have more than one crystal structure, depending on _______ & _______
temperature
pressure
Allotropic Materials
materials that change crystal structure depending on temperature
Upon completion of solidification, the colonies contact each other, forming ________
Grain boundaries
Metals deform more easily in directions along which __________ on planes of atoms that are ________ together
atoms are in closest contact
most tightly packed
Know how to find miller indices
**Screenshot of slide
Mechanical properties
response of the material to an applied force or stress
Important mechanical properties are
strength, ductility, stiffness, and hardness
Three principal ways in which a load may be applied
Tension(tensile test)
Compression(compression test)
Shear (shear test)
Lateral strains are _______ when the force is in tension
negative
_____ is always dimensionless
Strain
a linear portion on the stress-strain curve and the material will return to its original shape upon unloading
Elastic Region
in elastic region, stress-strain are proportional to each other
Hooke’s law
The ratio of the lateral and axial strains
Poisson’s Ratio
Larger _______ minimize elastic deflection
elastic moduli
What’s going on during elastic deformation?
Bond stretching during elastic deformation!
Elastic means _________ and __________
Elastic
Nonpermanent
modulus of elasticity is
a measure of stiffness of the material
Plastic Behavior
As the material is deformed beyond the yield strength point, permanent, or plastic deformation occurs
yield strength (proportional limit)
the initial departure from linearity of the stress-strain curve
What’s going on during plastic deformation?
Dislocation is moving during plastic deformation
Plastic deformation, or dislocation movement is __________
permanent
Yield Strength
Stress at which noticeable plastic deformation has
occurred
Tensile Strength
Maximum possible engineering stress in tension
When does tensile strength for metals occur?
when noticeable necking starts
Ductility
is the ability of a material to bend, stretch, or distort without breaking
plastic tensile strain at fracture
Percent Elongation (%PE)
A ductile material is ________
flexible
Brittle materials:
%EL
< 5%
Ductile materials:
%EL
> 5%
Toughness
The ability of a material to absorb energy up to fracture
For a material to be tough
it must display both _______ & _______
strength
ductility
This reversible behavior often shows a linear relation between stress and strain
Elastic behavior
This permanent deformation
Plastic behavior
the slope of the elastic portion
Young’s modulus
the stress at fracture
Fracture strength
The total energy absorbed during plastic deformation…. to break the material
Toughness
The plastic strain at failure
Ductility
Hardness
A measurement of a material’s resistance to penetration or localized plastic deformation
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
The softer the material, the ______ and ______ the indentation, and the _____ the hardness number
larger
deeper
lower
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
_________ is an accurate hardness measurement for soft materials
Brinell hardness (HB)
________ is the most widely used of all metal hardness testing methods
Rockwell hardness (HR)
_____ iron is much harder than the cast iron.
gray
Atomic vibrations are in the form of _______ or _______
lattice waves
phonons
Thermal Expansion (α )
Materials change size when temperature is changed
Polymers have larger α values because of ___________
weak secondary bonds
Thermal Conductivity
The ability of a material to transport heat.
Atomic vibrations and free electrons in hotter regions transport energy to cooler regions.
Atomic perspective
Why does thermal stress occur?
restrained thermal expansion/contraction
temperature gradients that lead to differential dimensional changes
The thermal properties of materials include:
Coefficient of thermal expansion
Thermal conductivity
Coefficient of thermal expansion
the size of a material changes with a change in temperature
polymers have the largest values
Thermal conductivity
the ability of a material to transport heat
metals have the largest values
Plastic deformation is __________ deformation.
permanent (non-recoverable)
_________ and _________ are measures of a material’s resistance to plastic deformation
Strength
hardness
During the plastic deformation, __________ must be ruptured and then reformed
interatomic bonds
In crystalline solids, plastic deformation most often involves the ___________
motion of dislocations
Edge Dislocation
associated with the edge of the extra half plane of atoms
Breaking the bonds together to _________ requires extremely large stress
facilitate slip
For metals, plastic deformation occurs by ______
slip – an edge dislocation slides over adjacent plane half-planes of atoms
A dislocation moves along a _______ in a _________ perpendicular to the dislocation line
slip plane
slip direction
The slip direction is the same as the ________ direction
Burgers vector
Slip plane
plane on which easiest slippage occurs
Highest planar densities
Slip directions
- directions of movement
Highest linear densities
BCC and FCC metals have a relatively ______ number of slip systems
large
Relatively ductile
HCP metals having _____ active slip systems
few
Relatively brittle
Dislocation Motion
Produces plastic deformation
Depends on incrementally breaking
bonds
During plastic deformation, the number of dislocations ________ dramatically.
increases
the separation of a body into two or more pieces in response to a static stress
simple fracture
Two general types of fracture
ductile
brittle
ductile
Slow crack propagation
Accompanied by significant plastic deformation
Fails with warning
brittle
Rapid crack propagation
Little or no plastic deformation
Fails without warning
______ fracture generally more desirable than _______ fracture
Ductile
Brittle
cup-and-cone fracture
moderately ductile
flat surfaces
brittle fracture
one piece
large deformation
Ductile fracture
many pieces
small deformations
Brittle fracture
What are the stages of Stages of Moderately Ductile Failure?
necking void nucleation void growth and coalescence crack propagation fracture
_____ fracture surface displays V-shaped, chevron markings
Brittle
V features point to the
crack initiation site
Transgranular crack propagation
through grains
Intergranular crack propagation
between grains
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
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
_____ are Stress Concentrators
flaws
Stress concentration ______ for sharp cracks—propagate at _____ stresses than cracks with blunt tips
higher
lower
Crack propagation for ductile materials ______
plastic deformation at crack tip when stress reaches yield strength—tip blunted—lowers stress conc.
Measure of material’s resistance to brittle fracture when a crack is present
Fracture Toughness
How to Reducing Stress Concentration ?
General Techniques
- Increase Fillet Radius (R)
- Reduce W/H ratio
