Week 9

Arrange the following polymer configurations in the decreasing order of the strength:

• Linear cross-linked branched reticulated

• Reticulated < cross-linked < branched < linear

• Linear branched cross-linked < reticulated

• Reticulated branched < cross-linked < linear

Select the appropriate polymer characteristics from the following options:

• The tensile strength of polymers decreases with increase in molecular weight

• The modulus of elasticity increases with an increase in crystallinity

• Annealing causes a decrease in crystallinity

• Mechanical properties are influenced by the rate of loading

State true or false:

Thermoplastic polymers usually show high creep, and it is a major problem in polymeric materials

• True

• False

The figure given below shows the specific volume vs temperature of materials A, B, and C. Select the appropriate answer from the following options.

• A-Amorphous and network polymer

• B-Semicrystalline and reticulated polymer

• C-Crystalline and reticulated polymer

• A-Amorphous and linear polymers

Under which one of the following conditions does the relaxation modulus observe a large drop in viscoelastic polymers?

• Temperature < glass transition temperature

• Temperature > glass transition temperature

• Temperature glass transition temperature

• Independent of temperature

Match the following additives with their effects on polymer properties:

• A-ii, B-iii, C-iv, D-i

• Aiv, B-iii, C-ii, D-i

• A-ii, B-i, C- iv, D-iii

• A-ii, B-i, C-iii, D-iv

Select the correct statements regarding particulate composite from the following options:

• The particle of rubber is used in automobile tyers to make them softer

• The alloys are generally manufactured by dispersion strengthening

• Wood is an example of continuous and aligned fibers in the transverse direction

• The fibers with a higher aspects ratio provide more tensile strength and toughness.

The modulus of elasticity of A and B are 100 GPa and 300 GPa, respectively. A composite is made up of these two materials in equal amounts. Calculate the upper and lower limit for the composite modulus.

• 150, 200

• 400, 200

• 200,400

• 200, 150

Calculate the critical aspect ratio of the fibers of radius 0.5 µm for the effective strengthening applications when the fiber strength in tension is 600 MPa, and the shear strength of the fiber-matrix interface is 50 MPa?

• 90

• 45

• 180

• 125