T or F

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

F

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

What is the relaxation modulus?

What is it's associated formula?

(hint: it's time dependent)

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

[image]

Where σ(t) is the measured time-dependent stress

ε₀ is the strain level.

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.  

1. True

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

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.

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

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

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.

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

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

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)

T or F

Vulcanization can occur on any carbon in a repeat unit.

Tor F

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

Upper Bound composite equation for elastic moduli:

When is this used?

[image]

Used when force is parallel to fiber alignment.

Lower Bound composite equation for elastic moduli:

When is this used?

[image]

Used when force is perpendicular to fiber alignment.

A fiber is continuous when?

A fiber is discontinuous when?

1. l > 15 x l_c

2. l < 15 x l_c

What is Ohm's Law?

Describe it's components in detail.

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)

Resistivity:

1. Description

2. Relation to Conductivity

3. Formula

1.A measure of how strongly a material opposes the flow of an electric current.

2. Inverse.

3. ρ=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

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

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

Definition:

Fermi energy

For a metal, the energy corresponding to the highest

filled electron state at 0 K.

Definition:

free electrons

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.

T or F

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

False - Such is the case for

insulators and semiconductors

Drift Velocity:

1. Description

2. Formula

1. The average electron velocity in the direction of the
force imposed by the applied field.

2. V_d = ξ μ_e

where μ_{e is the the electron mobility constant.(m²/V-s)}

_{ξ is is the electric field intensity (V/m)}

(or the voltage difference between two points divided
by the distance separating them)

σ = n|e|μ_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)

μ_e is the the electron mobility.

The total resistivity of a metal is the sum of the contributions from thermal vibrations, impurities, and plastic deformation.

ρ_total = ρ_t + ρ_i + ρ_d

Influences on Resistivity:

1. Temprature

2. Impurities

3. Deformation

1. ρ_t = ρ₀ + aT

where ρ₀ & a are 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 α & β

ρ_i = ρ_αV_{α +} ρ_βV_β

3. Plastic deformation also raises the electrical resistivity as a result of increased numbers of electron-scattering dislocations

σ = n_i|e|(μ_e + μ_h)

where n_i is the # of holes = free electrons

μ_e is the electron mobility

μ_h is the hole mobility

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

σ ≈ n|e|μ_e

where n is the # of free electrons

μ_e is the electron mobility

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

σ ≈ p|e|μ_h

where p is the # of holes

μ_h is the hole mobility

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

What is the degree of polymerization?

What is the equation?

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.

Define:

Isotactic

&

Syndiotactic

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.

1. Amorphus

2.Chain Bonds free to rotate

3. Cross Linking

4. must be above its glass transition temperature

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.

T or F

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

1.What is  capacitance?

2. What is the general formula?

3.What is the formula for a parallel capacitor separated by a vacuum?

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. ε₀A/l

1. What is electric field intensity ξ?

2. How does it relate to current density?

1.voltage difference between two points divided
by the distance separating them: ξ = V/l

2. current density J = ξσ

units of current per unit of area

1. What is the dielectric constant?

2. What is it used for?

1. it is the ratio of permittivity of a dielectric medium to permittivity of a vacuum.

ε_r = ε/ε_o

2. ε can be used in place of ε_o if there is not a vacuum between a parallel capacitor.

1. Equation relating frequency to wavelength for electromagnetic radiation.

2. How is energy related?

1. c = λv

where λ is wavelength & v is frequency

2. E = hv

where h is plank's constant (6.63 * 10^-34 Js)

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

2.Alternate form?

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

1. index of refraction n:

2. also equals

3.which approximates

1. n = c/v

where v = velocity of light in medium

2. (ε_rμ_r)^1/2

3. (ε_r)^1/2

where ε_r is the dielectric constant

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?

[image]

Where I₀ is incident beam of intensity

l is the specimen of thickness

β is absorption coefficient

& R is is the reflectance