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QUESTION 1 A semi-crystalline nylon with a degree of crystallinity of 25% has a density of 1.5 g/cm^3. Nylon has a crystalline density of 1.8 g/cm^3. What is its amorphous density in grams per centi...

QUESTION 1

  1. A semi-crystalline nylon with a degree of crystallinity of 25% has a density of 1.5 g/cm^3. Nylon has a crystalline density of 1.8 g/cm^3. What is its amorphous density in grams per centimeters cubed?

1 points   

QUESTION 2

  1. Which defect is NOT common between metals and polymers?

    tie molecules

    vacancies

    screw dislocations

    interstitial defects

0.5 points   

QUESTION 3

  1. Which one is not a characteristic of a plastic polymer?

    a.

    Low stress but very large strains

    b.

    Tensile strength is larger than the yield strength

    c.

    Tensile strength is lower than the yield strength

    d.

    Elastoplastic behaviour

0.5 points   

QUESTION 4

  1. Elastic modulus of carbon fibers is 260 GPa and the elastic modulus of titanium is 110 GPa. Design a carbon fiber reinforced titanium composite with longitudinal continuous fibers which has a longitudinal elastic modulus of 140 GPa. What is the volume fraction of fibers in percentage? Write your answer without the percentage symbol.

1 points   

QUESTION 5

  1. What is CORRECT about plastic polymers and ductile metals?

    both become more brittle at high temperatures

    both have lower tensile strength than the yield stress

    both become brittle by decreasing the strain rate

    both fail at the yield strength

0.5 points   

QUESTION 6

  1. What is the specific strength of a fiber with a density of 7.85 g/cm^3 and tensile strength of 450 MPa? Write your answer in GPa with 4 decimal points.

0.5 points   

QUESTION 7

  1. Which one is the property of Laminar composites?

    Overall anisotropic

    Layer-wise anisotropic

    Overall isotropic

    Single layered

0.5 points   

QUESTION 8

  1. For a "linear homopolymer with small molecules" which property is highly likely?

    high density

    high elastic modulus

    high hardness

    low ductility

0.5 points   

QUESTION 9

  1. Estimate the lower limit of the elastic modulus of concrete (50% gravel, 35% sand, and 15% cement) using the following information. Write your answer in MPa with 4 decimal points.

    Elastic modulus of gravel = 120 MPa

    Elastic modulus of clean sand = 50 MPa

    Elastic modulus of cement = 13 GPa

    Tip: Extend and use the rule of mixture to three components.

1 points   

QUESTION 10

  1. It is aimed to get the highest elastic modulus and strength at every direction in a composite. Which approach should be adopted?

    Randomly disperse the fibers and increase their aspect ratio

    Randomly disperse the fibers and decrease their aspect ratio

    Align the fibers and increase their aspect ratio

    Align the fibers and decrease their aspect ratio

0.5 points   

QUESTION 11

  1. Which one of the following polymers is more likely to be a thermoplastic?

    linear polymers

    branched polymers

    cross-linked polymers

    network polymer

0.5 points   

QUESTION 12

  1. Which one is CORRECT about particle-reinforced composites?

    Small particles bear the majority of the load.

    Large particles do not bear any loads.

    Dislocation arrest happens by both small and large particles.

    Both small and large particles have micro interactions with the matrix.

0.5 points   

QUESTION 13

  1. Which one is correct?

    a.

    The reinforcements of a composite can be fibers or particles.



    b.

    Small particles carry the majority of load in a composite.

    c.

    Cermets are composites with ceramic matrix and metallic particles.

    d.

    Large particles in a composite is called dispersions.

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Answer #1

20.2S 425 1-4

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