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Material Science 1 > Quiz 3 > Flashcards

Quiz 3 Flashcards

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1
Q

Brittleness

A

Tendency to fracture when even a small load/deformation is applied. Ex: glass

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2
Q

Ductile

A

How much a material can deform without sustaining internal damage. Ex: Gummy bear or rubber

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3
Q

Elasticity

A

Ability to return to the original shape after deforming/loading the material. Ex: rubber elastic

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4
Q

Plasticity

A

Ability of a material to stay deformed after external force is removed. Ex: blacksmith, I beams

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5
Q

Fatigue

A

Weakening pf a material due to repeated loading. Ex: Barbecue propane tanks

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6
Q

Hardness

A

The ability to resist permanent change in shape due to external loads. Ex: diamonds

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7
Q

Resilience

A

The ability to absorb energy and resist impact. Ex shock absorption or blast materials

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8
Q

Stiffness

A

Ability of a metal to resist additional deformation when loading continues.

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9
Q

Toughness

A

Ability of a metal to resist fractures. Ex: superheros

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10
Q

ASTM

A

The standard to quantify parameters and enable comparison of material properties

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11
Q

Engineering Stress

A

O= F/Ao
F -force
Ao- original area of the sample cross section

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12
Q

Engineering Strain

A

E = li-lo/lo or deltal/lo
li- instantaneous length
lo - original length

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13
Q

Creep

A

Deformation at elevated temperature (over a period of time)

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14
Q

Shear

A

t = F/Ao
y = alpha + beta given alpha and beta are in radians

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15
Q

Torsion

A

If we are not deforming by parallel plates, but by twisting the material.

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16
Q

Poissons ratio

A

For elastic behaving materials the tensile force in the z direction creates z strain -> Ez. This causes a contraction in the x and y directions. If the material is isotropic the. Ex and Ey are the same:
V = -Ex/Ez = -Ey/Ez

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17
Q

Relationship between shear and tension in elastic behavior

A

E = 2G(1+V)
E- elastic modulus
G- shear modulus
V- poissons ratio

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18
Q

Common poisson ratio for most material

A

0.3

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19
Q

Hookes Law

A

During the initial stage if loading a material the stress is proportional to the strain:
o = Ee
Stress = Elastic modulus x strain

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20
Q

Youngs modulus

A

E, the slop of the initial stress strain linear relationship. As temp increases the value if E decreases! We call this, that the material became less stiff. E is a measure of stiffness of the material

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21
Q

Relationship can be fir torsion and shear

A

Torsion = G shear (t =Gy)
Stress = E shear (o= Ee)

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22
Q

Plastic deformation

A

Many materials exhibit elastic behavior up to 0.005 strain or 0.5%. Above this strain the materials crystal bonds begin to fracture -> plastic deformation. The permanent change in material is possible by the movement of dislocations.

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23
Q

Yielding

A

The transition from E -> P regimen. In many many cases we do not wish to approach this load, but is is sometimes difficult to estimate when the transition from E to P happens. We can approximate by drawing a straight line starting at 0.002 strain. This line is parallel to the initial stress strain curve. Another common value is 0.005

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24
Q

Ultimate Tensile Strength

A

As the load continues to increase past yield, the dislocations move faster and start to combine. The dislocations form voids which form micro cracks which form cracks.

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25
Q

Ductility

A

When a material fractures, it is permanently gone. We would like to have as much as possible of a warning that failure is about to happen.
%Elongation = lf-lo/lo *100
%Area reduction = Ao-Af/ Af * 100

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26
Q

Resilience

A

Amount of energy absorbed in the elastic region
U = 1/2 oy^2/E

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27
Q

Toughness

A

Amount of energy absorbed up to fracture. Area under curve.

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28
Q

Polymorphism

A

Some metals as well as nonmetals may have more than one crystal structure.

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29
Q

Allotropy

A

When polymorphism is found an elemental solids.

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30
Q

Ficks first law

A

Steady state: (when the rate of diffusion into a system is equal to the right of diffusion out of the system. No net accumulation or depletion.)

Jx= -D (dc/dx)
Jx = Flux (or flow rate) of the diffusing species in the x direction due to a concentration gradient (dc/dx)
D= diffusion coefficient, or sometimes called diffusivity.
dc/dx - the change in concentration delta C/ over the change in dimension delta x

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31
Q

Ficks second law

A

Transient non-steady state conditions.
dCx/dt = d/dx(D dCx/dx)
If we assume a semi infinite solid, with a surface concentration of the diffusing species, Cs constant then we can solve using:
(Cx-Co)/(Cs-Co) = 1-erf(x/2sqrt(Dt))
X-position of interest
t-time of interest
Co- initial bulk concentration
Cs- surface concentration

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32
Q

Effects of Temperature on Diffusivity

A

D = Do e^(-q/kT)
Do- constant
q- activation energy to start moving defects, which consequently moves atoms.

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33
Q

Diffusion rates from fastest to slowest

A

Fastest, surfaces. Examples: catalytic, converters, photographic film.
Medium, grain boundary. Examples: critical for durability of interconnections in micro electronics.
Slowest, bulk (volume). Examples: a solid piece of material.

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34
Q

Weight percent

A

The weight of a particular element relative to the total alloy weight

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35
Q

Atom percent

A

The number of moles of an element in relation to the total moles of the element in the alloy

36
Q

Diffusion

A

Material transported by atomic motion

37
Q

Inter diffusion or impurity diffusion

A

The process by which atoms of one metal diffuse into another

38
Q

Self diffusion

A

Diffusion occurring in pure metals where atoms exchange positions for the same type of atom.

39
Q

What conditions must be met for Adams to diffuse?

A

For an atom to move, two conditions must be met. One there must be an empty adjacent site, and two the atoms must have sufficient energy to break bonds with its neighboring atoms, and then caused some lattice distortion during the displacement.

40
Q

Vacancy diffusion

A

One mechanism involves the interchanging of atoms from a normal lattice, position to an adjacent vacant, lattice site or vacancy.

41
Q

Interstitial diffusion

A

Adams that migrate from an interest position to neighboring ones that is empty. This mechanism is for the diffusion of impurities such as hydrogen, carbon, nitrogen, and oxygen which have atoms that are small enough to fit into the interstitial positions. Host or substitutional parties rarely form interstitial and do not normally diffuse via this mechanism.

42
Q

Diffusion flux

A

J- how fast do diffusion occurs or the right of mass transfer.
J = M/At
M- mass diffusing through
A- cross-sectional area
T- unit time

43
Q

Ficks first law

A

J =- D dC/dx
D: diffusion coefficient
dC/dx: concentration gradient

44
Q

Steady state diffusion.

A

The mass diffusing the species entering the plate on the high-pressure side is equal to the mass extending from the low pressure surface such that there is no net accumulation of diffusing species in the plate.

45
Q

Concentration profile

A

When concentration see is plotted versus position or distance within the solid X, the resulting curve is termed to the concentration profile.

46
Q

Concentration gradient

A

The slope at any given point of the concentration profile.

47
Q

Driving force

A

What compels a reaction to occur

48
Q

Are more practical diffusion, sit situation, steady state or non-steady state

A

Most are non-state so the diffuser flux and concentration at some particular point in solid vary with time

49
Q

Fix second law

A

dC/dt = D (d^2C/dx^2)
Or
(Cx-Co)/(Cs-Co) = 1-erf(x/2sqrt(Dt))

50
Q

What assumptions can be made about situations in which the surface concentration is held constant.

A

One. Before diffusion, any of the diffusing, a salute atoms in the solid are uniformly distributed with concentration Co.
Two. The value of X at the surface is zero and increases with distance into the solid.
Three. The time it taken to be zero the instant before the diffusion process begins.
T=0 C = Co at 0<=x<=infinity

51
Q

Carburizing

A

Increasing the surface, concentration of carbon.

52
Q

Factors that influence diffusion

A

Diffusion species, temperature

53
Q

Diffusion based on temperature formula

A

D = Do exp(-Qd/RT)
Do- a temperature independent pre-exponential
Qd- activation energy for diffusion
R-the gas constant 8.31 J per mole Kelvin
T- temperature in Kelvin

54
Q

Engineering Stres

A

o = F/Ao
o- stress

55
Q

Engineering Strain

A

e = li-lo/lo = delta l/ lo

56
Q

Stress strain relationship

A

O = Ee
o-stress
E- modulus of elasticity
e- strain

57
Q

Elastic deformation

A

Deformation in which stress and strain are proportional.

58
Q

Modulus of elasticity

A

E, this modulus may be thought of as stiffness or materials resistance to elastic deformation. The greater the modulus, the stiffer, the material, or the smaller, the elastic strain that results from the application of a given stress.

59
Q

Sheer stress,and strain relationship

A

t = Gy
t- shear stress
G- shear modulus
y- strain

60
Q

Poissons ratio

A

The ratio of lateral and axial stream
v = -ex/ez = -ey/ez
Commonly this race shows between 0.25 and 0.35

61
Q

Sheer modulus related to elastic modulus related to poisons ratio

A

E= 2G(1+v)

62
Q

Plastic deformation

A

Stress is no longer proportional to strain and permanent non-recoverable deformation occurs

63
Q

Yielding

A

The stress level at which plastic deformation begins.

64
Q

Proportional limit

A

The point of yielding may be determined as the initial departure from the line of the stress strain curve. This is sometimes called the proportional limit as indicated by point P.

65
Q

Tensile strength.

A

The stress at the maximum on the engineering stress straight and curve. This corresponds to the maximum stress that can be sustained by a structure, intention. If the stress is applied and maintained fractures will result. All deformations to this point is uniform throughout the narrow region of the tensile specimin

66
Q

Ductility

A

A measure of the degree of plastic deformation that has been sustained at fracture. A metal that experiences very, very little or no plastic deformation upon fracture is determined brittle. Maybe expressed by percent elongation or percent area reduction
%EL = (lf-lo/lo) 100
%RA = (Ao-Af/Ao)100

67
Q

How can you qualify brittle materials reference to ductility?

A

Bridle materials are approximately considered to have fracture strains of less than about 5%

68
Q

Resilience

A

The capacity of a material to absorb energy when it is deformed elastically, and then upon unloading to have this energy recovered. The associated property is the modulus of resilience Ur.

69
Q

Modulus of resilience definition

A

Ur = integral ( o )de
Integral of stress de strain from 0 to ey

70
Q

Modulus of resilience, assuming linear elasticity

A

Ur = 1/2 stressy strain y
Or
Ur= stressy^2/ 2E

71
Q

Toughness

A

Toughness is a mechanical term that is used in several context for one toughness is a property that is indicative of a materials resistance to fracture when a crack is present. Toughness is also the ability of a material to absorb energy and plastically deformed before fracturing.

72
Q

Stress to force relationship

A

Stress = Force/Area

73
Q

Tre stress and strain

A

From the engineering stress strain diagram it may appear that less stress is required to keep deforming the material.
The issue is that the cross sectional area decreases as we do the test, so true stress is increasing. True stress = Force/ instantaneous Area

74
Q

True stress

A

True stress = Force/ instantaneous area

75
Q

True strain

A

True strain = ln ( li/lo)
ln - natural log
li- instantaneous length
lo- original length

76
Q

True stress related to engineering stress and strain

A

True stress = engineering stress( 1+ engineering strain)

77
Q

True strain related to engineering stress and strain

A

True strain = ln( 1+ engineering strain)
ln- natural log

78
Q

Strain Hardening

A

Is related ti the slope if true stress vs true strain. The steeper the slope the more strain hardening

79
Q

Strain hardening formula

A

True stress = k*true strain^n
k-constant
n-strain hardening exponent

80
Q

Hardness

A

Provides a quantitative test to measure the resistance of a material to plastic deformation. These tests provide a way to measure plastic deformation without destroying the part.

81
Q

Rockwell test “HR”

A

Consists of a machine that applies a load onto a material:
- Indenter type
-magnitude of load
-time(dwell)
The deeper the impression the softer the material.

82
Q

Can a single hardness test be used on all materials?

A

No, scale for specific ranges of hardness is used

83
Q

Brinell Test “HB”

A

In this test, a steel ball is pressed against a material. This impression is ~mm wide.
Tensile strength (MPa) = 3.45 * HB
Tensile strength (psi) = 500 * HB

84
Q

Vickers Test “HV”

A

Typically done on a small scale to measure hardness of “delicate”, ie small, features. Impression is a pyramidal diamond. The bigger d1 and d2 (tip to tip measurements) the softer the material. Indent is smaller than human hair

85
Q

Fatigue

A

Fatigue is the type of failure where the material fails below its yield strength, because of cyclical loading.
Avg Stress = (max stress+minus stress)/2
Stress range(or) = max stress - min stress.
Amplitude = stress range/ 2
Stress Ratio (R) = max stress/min stress

86
Q

Is compression or tension the bigger enemy of fatigue?

A

Tension

Material Science 1 (3 decks)

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