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Biomaterials > Exam 1 (Ch. 3-4) > Flashcards

Exam 1 (Ch. 3-4) Flashcards

1
Q

an _____ dislocation occurs when an extra portion of a plane of atoms in a crystal ends (perpendicular)

A

edge (1D)

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2
Q

the Burger’s vector does what?

A

completes the atomic circuit

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3
Q

a _______ dislocation occurs when shear forces cause a portion of a crystal to move one atomic distance relative to the other portion (parallel)

A

screw (1D)

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4
Q

Burger’s vectors are longer for (ceramics/metals). Why?

A

ceramics, because of the electroneutrality requirement - this is why they exhibit more brittle fracture

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5
Q

dislocations allow _______ deformation of a crystalline material via dislocation glide

A

plastic

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6
Q

dislocations move similarly to what creature?

A

caterpillar (one atomic distance at a time)

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7
Q

dislocation glide occurs more easily on planes with (high/low) atomic density. why?

A

high. the “steps” required to move each atomic distance are smaller, and thus require less energy

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8
Q

plastic deformation in crystals is called ______ and occurs in the _______ plane

A

slip, slip plane

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9
Q

atoms at the surface of a material have (higher/lower) energy than those inside a crystal, leading to surface free energy or surface tension

A

higher

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10
Q

the interface between grains is called the…

A

grain boundary

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11
Q

grain boundaries have (higher/lower) energy

A

higher

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12
Q

the greater the angle of misorientation between two grain boundaries, the (higher/lower) the energy

A

higher

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13
Q

_____ boundaries are formed when edge dislocations align

A

tilt (2D)

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14
Q

______ boundaries are formed when screw dislocations align

A

twist (2D)

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15
Q

_______ boundaries are formed when a mirror image of atomic placement occurs across a boundary

A

twin (2D)

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16
Q

do corrosive attacks in metals begin at the grain boundaries or at the center of the grains? why?

A

grain boundaries, they are higher in energy and want to participate in reactions

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17
Q

__________ are 3D defects formed from clusters of substitutional or interstitial impurities

A

precipitates

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18
Q

_________ are 3D defects formed from clusters of vacancies

A

voids

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19
Q

voids form what 3D defect that is sometimes controlled to alter biological response?

A

pores

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20
Q

__________ are added during implant fabrication to create pores

A

porogens [solid (NaCl or gelatin) or gaseous (N2 or CO2)]

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21
Q

pores are also sometimes formed by weaving ________ together to form a mesh containing large voids

A

fibers

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22
Q

list some advantages of porous materials

A

they allow for exchange of fluids and gases deep within the material, they encourage tissue ingrowth and implant anchoring (downside is greater rate of degradation and corrosion)

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23
Q

(atactic/isotactic/syndiotactic) polymers have a much harder time crystallizing

A

atactic - hard to form ordered structures

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24
Q

the basic unit of crystalline structure is the…

A

lamella (chain-folded model)

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25
_________________ connect lamella together in amorphous regions
tie molecules
26
when polymers are crystallized from a molten state, ____________ form, 3D aggregates of lamellae that are analogous to grains
spherulites
27
(metals/ceramics/polymers) have the longest Burger's vectors
polymers, because their unit cells are so large
28
what mechanism of deformation occurs in noncrystalline materials?
viscous flow
29
the _______________ is the temperature below which the material acts as a solid, seen in ceramics and amorphous polymers
glass transition temperature, Tg
30
the working point occurs at ______ P
10^4 P
31
higher amounts of branching in a polymer will (increase/decrease) the melting temperature
decrease
32
higher molecular weight will (increase/decrease) the melting temperature and glass transition temperature
increase
33
a polymer with more flexible chains will have a (higher/lower) glass transition temperature
lower, easier to move around energetically
34
polar side groups that promote chain interactions (increase/decrease) glass transition temperature
increase
35
cross-linking (increases/decreases) glass transition temperature
increases
36
at the _____________ temperature, polymer chains have enough energy to move into a highly ordered state
crystallization temperature (Tc)
37
polymers are __________ by raising the temp to the Tc, maintaining this temp for some time, and then slowly cooling
annealed
38
DSC, a popular thermal analysis technique that provides a material's transition temperatures, stands for what?
differential scanning calorimetry
39
more area under the Tm peak implies (higher/lower) crystallinity
higher
40
on a DSC plot, peaks are (exothermic/endothermic) and valleys are (exothermic/endothermic)
peaks are endothermic, valleys are exothermic
41
large grains (less boundary area) or small grains (more boundary area) are stronger
small grains - the slip plane is very rough, hard for dislocation motion, HOWEVER, will degrade faster
42
percent crystallinity formula
c(s-a)/s(c-a) x 100 (CSA-SCA)
43
higher % plasticizer (increases/decreases) glass transition temperature
decreases
44
testing samples are shaped like what for tensile testing
dog bones (easy for the frame to hold on to the ends)
45
engineering stress (σ) is calculated by...
F/A (where A is initial A)
46
engineering strain (ε) is calculated by...
ΔL/L (where L is initial L)
47
testing samples are shaped like what for compressive testing
cylinders
48
shear testing applies force where?
parallel to the top and bottom faces of the sample
49
shear strain is calculated how?
tan(θ) where θ is the angle of sample deformation
50
Hooke's law
σ = Eε (E = modulus of elasticity, or the slope of the stress-strain curve)
51
Poisson's ratio
v = - εt/εa
52
a high E (Young's modulus) implies a material is very...
stiff
53
plastic deformation begins at what point on a stress-strain curve
when the linear portion ends
54
the yield strength occurs where on the stress-strain curve
the stress at the end of the elastic (linear) region
55
the ultimate tensile strength occurs where on the stress-strain curve
at the maximum of plastic deformation
56
ductility is the ability of a material to do what?
deform plastically before fracture
57
true stress is calculated how
F/A (where A is A instantaneous)
58
true strain is calculated how
ln(li/l0)
59
polycrystalline materials are (stronger/weaker) compared to single-crystal materials
stronger due to constraints by neighboring grains (harder for dislocation motion)
60
________ is plastic deformation of a sample under constant stress over time
creep
61
________ is the decrease in stress seen when under constant strain over time (think old rubber band)
stress relaxation (most common in polymers)
62
what's an example of a viscoelastic material?
silly putty
63
reminder to review Maxwell and Voigt models!
reminder to review Maxwell and Voigt models!
64
(ductile/brittle) fracture is preferred. why?
ductile, because there is warning (plastic deformation)
65
________, similar to cracks, occur in amorphous plastic polymers and can support a load but weaken the material
crazes
66
define and describe stress raisers (aka stress concentrators)
small flaws can lead to large cracks or crazes because they amplify applied stress at the tip of the flaw
67
notches, sharp corners, and pores are examples of...
stress raisers
68
___________ is the cause of up to 90% of metallic fractures
fatigue
69
what are the three stages of fatigue failure?
crack initiation --> crack propagation --> final failure
70
fatigue life N = what?
Ni (initiation) + Np (propagation)
71
__________ ________ is the stress level that will cause failure after a given number of cycles
fatigue strength
72
failure that occurs because of the presence of cyclic stresses in combination with chemical attack is called...
corrosion fatigue
73
what is the key principle behind strengthening biomaterials?
reducing the movement of dislocations
74
similar to alloys for metals, ______ can be added to polymers to add crosslinks and reduce chain motion (strengthening)
fillers (carbon nanotubules are an example)
75
describe grain growth at high temperatures
larger grains grow while smaller ones shrink, increasing the overall grain size and decreasing grain boundary area
76
why does very rapid cooling result in a low percent crystallinity?
the chains need time to align and form crystals

Biomaterials (6 decks)

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