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Marianne Advanced and Applied > Dynamic Mechanical Analysis (DMA) > Flashcards

Dynamic Mechanical Analysis (DMA) Flashcards

1
Q

What are the basic principles of DMA?

A
  1. Measures mechanical or viscoelastic properties.
  2. Sinusoidal force applied to sample.
  3. Resulting displacement measured.
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2
Q

What material is said to be viscoelastic?

A

Material with both elastic and viscous (time dependent) behavior.

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3
Q

What are the parameters measured in DMA?

A
  1. Stiffness (modulus values).
  2. Tg.
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4
Q

What are the two modulus values and what behaviors do they represent?

A
  1. Storage modulus - elastic behavior
  2. Loss modulus - inelastic behavior
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5
Q

What is the glass transition temperature Tg?

A

Where crystalline domain loses its structure, or melts.

-
Temperature which amorphous domains lose structure mobility of polymer chains - become rigid glasses.

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6
Q

What is the Storage Modulus? give the equation.

A
  1. The ability of material to store energy
  2. elastic properties
  3. E’(MPa) = stress / strain x cosδ
  4. Similar to stiffness
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7
Q

What is the loss modulus,what properties does it show, state the equation?

A
  1. Heat dissipated from material due to molecular motions
  2. damping & viscous properties
  3. E’‘(MPa) = stress / strain x sinδ
  4. similar to viscosity
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8
Q

What is the complex modulus?

A
  1. Material’s resistance to deformation.
  2. E* = E’ + iE’’
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9
Q

What is the tan δ?

A
  1. Ratio of the dissipated energy to energy stored.
  2. Tan δ = E’’ / E’
  3. damping properties.
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10
Q

What are the two significant tan δ values?

A

Tan δ = 0, pure liquid (purely elastic materials)
Tan δ = ∞, δ = 90° (visco-elastic materials)

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11
Q

What is measured by DMA, express units?

A

S = stiffness (N/m)
k = geometry constant (m-1)

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12
Q

What is calculated by DMA, express units?

A

Modulus (Pa): E = S/k

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13
Q

How is the geometry constant (k) calculated?

A

Tension& Compression:
k = A/l
A: cross-sectional area
I: free length

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14
Q

What are the different geometries?

A
  1. single cantilever
  2. Dual cantilever
  3. 3 point bending
  4. simple shear
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15
Q

What is the equation for single cantilever geometry?

A

k = w(t/l)3

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16
Q

What is the equation for dual cantilever geometry?

A

k = 2w (t/l)3

17
Q

What is the equation for 3 point bending geometry?

A

k = w (t/l)3 / 2

18
Q

What is the equation for simple shear geometry?

A

k = 2A / t

19
Q

What is the modulus for rubbery state?

A

10^6 Pa

20
Q

What is the modulus for glassy state?

A

10^9.5 Pa

21
Q

What is the optimum geometry constant?

A

10^(-3.5) to 10^(-2) Pa

22
Q

When do you choose the simple shear geometry and why?

A
  1. For rubbers and gels, because of stiff geometry.
  2. used for samples with modulus 10^7 or less.
23
Q

When do you choose the tension geometry and why?

A

Superimpose static force (larger), because sample remains under net tensile force (prevents buckling of sample)

24
Q

When do you choose the single and dual cantilever, and bending geometry and why?

A

For samples of thickness at least 2mm.
- Single cantilever: relax thermal stresses
- 3-point bending: high modulus materials - accurate modulus determination.

25
Q

What are the measurement modes?

A
  1. Bending - single cantilever clamp
  2. Tension - tensile clamp
  3. 3-point bending
  4. shear
26
Q

What is considered when applying strain,what occurs in a linear and non-linear region?

A
  1. Small loads and strains (0.1 - 1%)
  2. Linear viscoelastic region - constant modulus value independent of strain
  3. Non-linear behavior region - strain increased, modulus drops
27
Q

How do you check if the material is within its linear viscoelastic region? (for calibration)

A

Perform strain scan (0.1 - 5%) on glassy material.
If modulus remains constant - measurement is in linear range.

28
Q

What happens with the levels of vinyl acetate?

A
  • More Vinyl Acetate
  • More viscoelastic copolymer
29
Q

What are applications of DMA-RH?

A

Measures changes on mechanical properties (modulus, extension) in controlled RH, of:
1. canvas (cellulose)
2. Parchment (collagen)
3. textiles (wool)
4. wood

Marianne Advanced and Applied (17 decks)

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