Question

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.

Answer 1

20.2S 425 1-4