Exam 1 Flashcards
How large is a subatomic structure?
<1A
How large is an atomic structure?
1A
How large is a microstructure?
nm to mm
How large is a macrostructure?
> 1mm
What are the 5 types of materials?
Metals, ceramics, polymers, composites, advanced materials
What is an alloy?
Mixture of two or more elements
What is unique about metals and electrons?
Large number of nonlocalized electrons
What is ductility?
Measure of materials ability to undergo plastic deformation before fracture
Ceramics are a compound of what?
Metallic and non-metallic elements
Optically, ceramics may be?
Transparent, translucent, or opaque
Polymers are?
Organic compounds that are chemically based on C H, and non-metallic elements
Polymers have _ molecular weight?
High
Polymers are what in regards to density and ductility?
- Low density
- Extremely ductile
What is a composite?
2+ individual materials
What are material property charts?
Two material properties plotted against each other
What are the 4 different types of advanced materials?
Semiconductors, biomaterials, smart materials, nanomaterials
What are nano-materials?
10-100nm
What is affected when you reduce the size of a material?
Optical properties
What are the 4 ways to apply load?
Tension, compression, shear, torsional
Explain tension tests
- Destructive test that measures stress and strain as a function of time
What are the equations for stress and strain with a tension test?
Stress = F/A Strain = delta l/lo
What are the equations for shear stress and strain?
Stress = F/A Strain = tan theta = delta x/y
During torsional tests, what does phi mean?
Angle of twist
What are the equations for tensile stress and shear stress for a torsional test?
T Stress = σ (1+cos 2theta/2)
S Stress = σ (sin2theta/2)
Explain hooke’s law
σ = E * e
Tensile stress = modulus of elasticity * strain
What is the modulus of elasticity?
Stiffness or resistance to elastic deformation
Explain the stress-strain diagram
σ vs e, slope = E
Shows elastic deformation
What is elastic deformation?
Stress and strain are linearly proportional
Where is the elastic portion of the stress-strain curve?
When the curve isn’t linear
What is elastic strain?
Small changes in interatomic spacing
What is the relationship between the temperature and modulus of elasticity?
As T goes up, E goes down
What is the relationship between shear stress and shear strain
τ = G *γ
shear stress= shear modulus * shear strain
What is anelasticity?
Time dependent elastic behavior
What is anelastic behavior called for polymers?
Viscoelastic behavior
Explain poisson’s ratio
v = negative ration of transverse and longitudinal strains
What is the modulus of elasticity for isotropic materials?
E = 2G (1+v)
For anisotropic materials, what does the modulus of elasticity depend on?
Crystallographic direction
What is happening during plastic deformation?
Bonds break and form
Elastic deformation is _ and plastic deformation is _
Nonpermanent, permanent
What is yield strength (σy)
Measure of resistance to plastic deformation
What is tensile strength?
Max stress that can be sustained in tension
What is the yield strength associated with?
Lower yield point
What are the two measure of ductility?
% Elongation and % Area Reduction
What is resilience?
Capacity of a material to absorb energy when deformed elastically and recovered (Ur)
What is the relationship between stress and the modulus of elasticity in regards to resilient materials?
When stress is high, E is low
What is toughness?
Materials resistance to fracture when there’s a crack
Ability of a material to absorb energy and plastically deform before fracturing
What are the equations for true stress and strain?
σt = F/Ai et = ln(li/lo)
What is hardness?
Material’s resistance to localized plastic deformation
Yielding occurs when?
Onset of plastic deformation
How do you calculate the average atomic weight of an element?
A = sum( fi*Ai)
fi - fraction of occurrence of isotope
Ai - atomic weight
Explain the Bohr atomic model
Different orbitals/energy levels for electrons. Going to a higher level = absorption of energy
Going to lower level = emission of energy
What are quantized electrons?
Electrons permitted to have only specific values of energy
Explain the wave-mechanical model of atoms
The electron is both a wave and particle, position is a probability of being at various locations around the nucleus
What do quantum numbers describe?
Shape, size, orientation of an electron
What is the Pauli exclusion principle?
Each electron state has no more than 2 electrons, having opposite spins
Electropositive elements want to do what with electrons?
Give them up
As you go up and right of the periodic table, how does electronegativity change?
Increases
What is the relationship between bonding energy and melting temperature?
Large bonding = High melting
What are the three types of bonds?
Ionic, covalent, metallic
What does an electron cloud look like?
Ion cores with valence electrons in between so positive cores don’t repel each other
Van der Wall bonding occurs between?
Dipoles
We can find % ionic character when?
We have covalent-ionic mixed bonding
What is the relationship between bond energy and melting temp?
Larger Eo, higher Tm
Relate bond energy, melting temp, modulus of elasticity, and coefficient of thermal expansion to ceramics
Large, high, large, small
Relate bond energy, melting temp, modulus of elasticity, and coefficient of thermal expansion to metals
Variable, moderate, moderate, moderate
Relate bond energy, melting temp, modulus of elasticity, and coefficient of thermal expansion to polymers
Weak between chains, low, small, large
Van der Wall bonds are _ than primary bonds
Weaker
What are the two classes of structures when materials solidify?
Glassy/amorphous/noncrystalline , crystalline
Why is atomic packing dense for metals?
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
What are the 4 types of metallic crystal structures?
SC, FCC, BCC, HCP
What is the coordination number?
Number of nearest-neighbor atoms
What is the atomic packing factor?
Vol of atoms in unit cell/ Vol of cell
What is the coordination number for SC?
6
How to find the vol of atoms in a unit cell?
atoms N * vol of atom
What is the coordination number for FCC?
12
What is the coordination number for BCC?
8
What is the coordination number for HCP?
12
Equation for density?
nA / VcNa # atoms per unit cell * atomic weight/ Vol unit cell * avagadro's number
Rank the densities of metals, ceramics, and polymers
Metal> ceramic> polymer
What is polymorphism?
Material has more than one crystal structure
Allotropy is polymorphism in?
Elemental solids
Equivalent crytallographic directions are called?
Families
What is planar density?
atoms centered on a plane/Area of plane
What is the packing sequence for HCP?
ABAB
What is the packing sequence for FCC?
ABCABC
What is anisotropy?
Physical properties dependent on the crystallographic direction
What are grain boundaries?
Boundary region separating two grains with atomic mismatch
What is X-ray diffraction?
Technique used for determination of crystal structures
When does diffraction occur?
Wave encounters regularly spaced obstacles
During constructive interference, amplitudes are?
Added
During destructive interference, amplitudes?
Cancel
As crystal symmetry decreases, XRD peaks?
Increase
Peak positions are determined by?
Size, shape of unit cell
Peak intensities are determined by?
Atomic number and position of atoms
Peak widths are determined by?
Instruments, temp, crystal size, strain, imperfections
Amorphous structures are due to?
Rapid cooling
What are the 7 crystal systems?
Cubic, tetragonal, hexagonal, orthorhomic, rhombohedral, monoclinic, and triclinic
Single crystals are?
Atomic order extends uninterrupted over the entirety of the specimen
For isotropic materials, properties are?
Independent of the direction
Noncrystalline materials lack?
Systematic and regular arrangement
Noncrystaliine materials are also called?
Amorphous
