question

T or F
Viscoelastic deformation is instantaneous, which means that total deformation occurs the instant the stress is applied or released.

answer

F

Elastic deformation is time independent while Viscoelastic deformation is time dependent.

question

What is the relaxation modulus?

What is it's associated formula?
(hint: it's time dependent)

answer

The stress necessary to maintain a predetermined
strain level in a viscoelastic material.

[image]
Where σ(t) is the measured time-dependent stress
ε₀is the strain level.

question

T or F

1. The higher the temprature of a viscoelastic specimen, the lower the Relaxation Modulus.

2. The temperature dependence for an almost totally
crystalline material the more pronounced glass region it will exibit.

answer

1. True

2. False - The greater the crystallinity of a specimen the less pronounced the drop in temprature at T_g

question

T or F

1. As a general rule the susceptibility to creep decreases as the degree of crystallinity increases.

2. The creep modulus is also temperature sensitive and increases with increasing temperature.

answer

1. True - (this means Creep modulus E_c(t) will increase)

2. False - Creep Modulus is temprature dependant, but will diminish as temprature increases.

question

As a general rule, the mode of fracture in thermosetting polymers is brittle. Why?

answer

Thermosetting polymers have heavily cross-linked networks which prevent plastic deformation.

question

T or F

The onset of elastic deformation for semicrystalline polymers results from chain molecules in crystalline regions elongating in the direction of the applied tensile stress.

answer

False - chain molecules in amophous regions allow elongation.

question

What are some factors that affect the Tensile Strength of polymers?

How can a polymer be modified such that TS is improved?

answer

1. •Average Molecular Weight - The higher the AMW the higher the TS.
. •Degree of Crystallinity - for semicrystaline polymers increasing the DoC increases TS, but makes brittle.

2. •Predeformation by Drawing - Tensile modulus in the direction of drawing is increased by orienting chains.
•Heat Treating - (increases degree of crystallinity)

question

In what material does the modulus of elasticity increases with increasing temperature, which is opposite to the behavior found in other materials?

answer

ELASTOMER

question

Fraction crystallized y is a function of time according to the Avrami equation:

answer

[image]

question

T or F

Vulcanization can occur on any carbon in a repeat unit.

answer

False - It can occur on any carbon sharing a double bond.

question

Tor F

For most composites, the particulate phase is harder and stiffer than the matrix.

answer

True

question

Upper Bound composite equation for elastic moduli:

When is this used?

answer

[image]

Used when force is parallel to fiber alignment.

question

Lower Bound composite equation for elastic moduli:

When is this used?

answer

[image]

Used when force is perpendicular to fiber alignment.

question

A fiber is continuous when?

A fiber is discontinuous when?

answer

1. l > 15 x l_c

2. l < 15 x l_c

question

σ'_m is?

answer

stress on composite matrix when fiber fails.

question

What is Ohm's Law?

Describe it's components in detail.

answer

V = IR
;
V is Voltage (potential difference) ; Volts (J/C)
I is Current ; Amperes (C/s)
R is Resistance ; Ohms (V/A) (A is amperes)
;
C is Charge ; Coulomb (A*s)

question

Resistivity:
;
1. Description
;
2. Relation to Conductivity
;
3. Formula

answer

1.A measure of how strongly a material opposes the flow of an electric current.
2. Inverse.
3. ;=RA/l
where: R is resistance.
A is the cross-sectional area perpendicular to the direction of the current.
l is the distance between the two points at which the voltage is measured

question

The electrical properties of a solid material are a consequence of:

answer

...the arrangement of the outermost electron bands and the way in which they are filled with electrons.

question

Definition:
;
;
Fermi energy

answer

For a metal, the energy corresponding to the highest
filled electron state at 0 K.

question

Definition:
;
;
free electrons
;

answer

Electrons with energies greater than the Fermi energy
may be acted on and accelerated in the presence of an
electric field.These are the electrons that participate in the conduction process.

question

T or F
;
For metals, empty states adjacent to the top of the filled valence band are not available.

answer

False - Such is the case for
insulators and semiconductors

question

Drift Velocity:
;
1. Description
;
2. Formula

answer

1. The average electron velocity in the direction of the
force imposed by the applied field.
;
2. V_d =;; ;_e
where ;_e_{is the the electron mobility constant.(m²/V-s)}
_{; is is the electric field intensity (V/m)}
(or the voltage difference between two points divided
by the distance separating them)

question

Conductivity formula: ;

answer

; = n|e|;_e
;
where n is the number of free or conducting electrons per unit volume.
|e| is the absolute magnitude of the electrical charge on an electron (constant value of 1.6 x 10^-19 C)
;_e is the the electron mobility.

question

What is Matthiessen;s rule?

answer

The total resistivity of a metal is the sum of the contributions from thermal vibrations, impurities, and plastic deformation.
;
;_total = ;_t + ;_i + ;_d

question

Influences on Resistivity:

1. Temprature

2. Impurities

3. Deformation

answer

1. ;_t = ;₀ + aT
where ;₀; aare constants for each particular metal.
2. Given on Test
where c_i is the impurity concentration ; A is a constant regarding both the impurity and host metals.
or for a 2-phase alloy consisting of ; ; ;
;_i= ;_;V_; ₊ ;_;V_;
3. Plastic deformation also raises the electrical resistivity as a result of increased numbers of electron-scattering dislocations

question

Conductivity of a pure intrinsic semiconductor.

answer

; = n_i|e|(;_e + ;_h)
;
where n_i is the # of holes = free electrons
;_eis the electron mobility
;_his the hole mobility
|e| is the absolute magnitude of the electrical charge on an electron (constant value of 1.6 x 10^-19 C)

question

Conductivity of a n-type extrinsic semiconductor.

answer

;;; n|e|;_e
;
where n is the # of free electrons
;_eis the electron mobility

|e| is the absolute magnitude of the electrical charge on an electron (constant value of 1.6 x 10^-19 C)

question

Conductivity of a p-type extrinsic semiconductor.

answer

;;; p|e|;_h
;
where p is the # of holes
;_his the hole mobility

|e| is the absolute magnitude of the electrical charge on an electron (constant value of 1.6 x 10^-19 C)

question

What is the degree of polymerization?
;
What is the equation?

answer

1.the average number of repeat units in a polymer chain.
;
2. DP = M_n/m
Where M_n is the number average molecular weight. and m is the molecular weight of the repeated unit.

question

Define:
;
Isotactic
;
;
;
Syndiotactic
;

answer

1.A type of polymer chain configuration (stereoisomer) wherein all side groups are positioned
on the same side of the chain molecule.
;
2. A type of polymer chain configuration (stereoisomer) in which side groups regularly alternate positions on opposite sides of the chain.

question

How do you calculate the degree of polymerization for a copolymer?

answer

;;(molefraction_i*molecularweight_i)

question

4 criteria for a polymer to be elastomeric:

answer

1. Amorphus
;
2.Chain Bonds free to rotate
;
3. Cross Linking
;
4. must be above its glass transition temperature

question

Explain the change of specific volume (1/;) with regards to increased temperature for glasses, semicrystalline, and crystalline polymers.

answer

SV goes up linearly with increasing temperature until it meets the glass temperature. At this point the slope increases. For a glass, the change in slope is large, for a semicrystalline polymer, the change is small, for a crystalline polymer, it is negligible.

question

T or F
;
the properties of a composite having its fibers aligned are highly anisotropic, that is, dependent on the direction in which they are measured.

answer

True

question

T or F
;
Isostrain conditions correspond to the "lower limit" or traverse strain behaviors for fiber and matrix phases.

answer

False - Isostrain condition corresponds with the "upper limit" or longitudinal strain behaviors.

question

How does the elastic modulus differ for a radndom oriented fiber composite than that of an aligned?

answer

A constant K is added to the Fiber term where K is the fiber efficiency constant and depends on V_f

question

1.What is; capacitance?
;
2. What is the general formula?
;
3.What is the formula for a parallel capacitor separated by a vacuum?

answer

1. the magnitude of charge stored on either
plate divided by the applied voltage.
;
2. C = Q/V
Where Q is the quantity of charge stored on either plate ; V is the voltage applied across the capacitor.
;
3. ;₀A/l
;

question

1. What is electric field intensity ;?
;
;
2. How does it relate to current density?

answer

1.voltage difference between two points divided
by the distance separating them: ; = V/l
;
2. current density J = ;;
units of current per unit of area

question

1. What is the dielectric constant?
;
2. What is it used for?

answer

1. it is the ratio of permittivity of a dielectric medium to permittivity of a vacuum.
;_r = ;/;_o
;
2. ; can be used in place of ;_oif there is not a vacuum between a parallel capacitor.

question

1. Equation relating frequency to wavelength for electromagnetic radiation.
;
2. How is energy related?

answer

1. c = ;v
where ; is wavelength ; v is frequency
;
2. E = hv
where h is plank's constant (6.63 * 10^-34 Js)

question

1. Equation for the intensity of the beam incident to the surface of the solid medium.

2.Alternate form?

answer

1. I₀ = I_T + I_A + I_R
(intensities of the transmitted, absorbed, and reflected beams)

2. T + A + R = 1
where X = I_X/I₀

question

1. index of refraction n:

2. also equals

3.which approximates

answer

1. n = c/v
where v = velocity of light in medium

2. (ε_rμ_r)^1/2

3. (ε_r)^1/2

where ε_ris the dielectric constant

question

T or F

Energy excitations with the accompanying absorption can take place only if the photon energy is greater than that of the band gap E_g?

answer

True

question

transmitted intensity I_T is given by the formula:

answer

[image]
Where I₀ is incident beam of intensity
l is the specimen of thickness
β is absorption coefficient
& R is is the reflectance

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