University of Ontario Institute of Technology

ENGR 2220A

Quiz 4

1)Which of the following polymers is most abundantly used?

1. Polyethylene
2. Polystyrene
3. Polyvinylchloride
4. Polypropylene

2. Which of the following polymers can be formed in extremely long chain structures which can be used as replacement of Kevlar in bullet proof vests?

1. Polyethylene
2. Polystyrene
3. Polyvinylchloride
4. Polypropylene

3. At temperatures below glass transition temperature, the polymers are

1. Quite stiff and tough
2. Quite stiff and brittle
3. Exhibit large visco-elasticity
4. Rubbery and ductile

4. Which of the following polymer is thermoset:

1. Polyethylene
2. Polystyrene
3. Polyvinylchloride
4. Cross-linked Rubbers

5. Polymers are composed of long chained molecules. Generally the element forming the backbone of the chains by covalent bonds is

1. Oxygen
2. Hydrogen
3. Silicon
4. Carbon

6. A better definition of elastomer is:

1. Materials which melt on heating and solidify on cooling due to the van der Waal forces between adjacent molecules
2. Materials with long chained molecules
3. Materials which exhibit large deformation under stresses from which they recover when the load is removed
4. Materials which can sustain large amounts of plastic deformation

7. Which statement best fits the blank space:

Thermoplastic polymers solidify by                     between adjacent molecular chains at lower temperatures.

1. forming van der Waal bonds
2. increased chain entanglement
3. reduced molecular motion

8. In general the molecular weight of polymers is in the range

a. 1 -100 g/mol

b. 100 -1,000 g/mol

c. 10,000 -1,000,000 g/mol

d. Over 1,000,000 g/mol

9. Polymers can be strengthened by orienting them. This is done by

1. special mechanical processing which aligns all the dislocations perpendicular to the strengthening direction
2. special heat treatment processing which aligns all the molecular chains perpendicular to the strengthening direction
3. stretching, which aligns all the molecular chains perpendicular to the strengthening direction
4. stretching, which aligns all the molecular chains parallel to the strengthening direction

10. Which polymer is widely used as insulation and in packaging industry due to its good foaming properties.

1. Polyethylene
2. Polystyrene
3. Polyvinylchloride
4. Polypropylene

11. The cermets are

1. A ceramic primary phase imbedded with a secondary phase, which usually consists of fibers
2. A metallic primary phase imbedded with a secondary phase, which usually consists of ceramics
3. A polymeric primary phase imbedded with a secondary phase, which usually consists of ceramics

12. Which ONE statement is true for polymer spherulites

1. These are 100 % crystalline regions surrounded by an amorphous matrix material
2. These are 100 % amorphous regions surrounded by crystalline matrix material
3. These are granular structures containing both crystalline and amorphous regions.

13. Which of the following composites are classifications based upon the matrix materials

a. Ceramic matrix composite, Carbon fiber composites, polymer matrix composites b, . Polymer matrix composites, Ceramic matrix composite, Metal matrix composites,

c. Boron fiber composites, Metal matrix composites, Polymer matrix composites

14. The mer of thermoplastic Polystyrene (PS) is similar to polyethylene mer with

1. a chlorine atom replacing a hydrogen atom
2. a chlorine atom replacing a hydrogen atom
3. a silicate {1 silicon, 4 oxygen} molecule replacing a hydrogen atom
4. a phenyl {6 carbon, 5 hydrogen} molecule replacing a hydrogen atom

15. During three point loading test, the maximum tensile strength occurs at

1. the point of maximum deflection and the outer most concave layer
2. the point of maximum deflection and the outer most convex layer
3. the point of maximum deflection and the central layer

16. Which of the following statements about composites is NOT correct? Composites:

1. Are very strong and stiff, yet very light in weight
2. Have ratios of strength?to?weight and stiffness?to?weight, several times greater than steel
3. Are equally strong in all direction
4. Have generally better fatigue properties

17. Which of the following disadvantages DO NOT apply to composites? Composites:

1. Properties can be anisotropic – this may be a disadvantage in some cases
2. Are heavier in weight
3. Are generally more expensive
4. Manufacturing methods are often slow and costly

18. Which of the following statements is NOT true?

1. Branched polymers are generally weaker than linear polymers
2. Polymers having long and linear chains can sustain large deformations
3. Networked polymers have higher strength that lightly cross-linked polymers
4. Cross-linking of polymers makes them thermoset materials

19. Atomic Packing Factor is

1. the ratio of number of whole atoms in a unit cell to the total number of atoms that the unit cell intersects
2. the ratio of weight of whole atoms in a unit cell to the weight of total number of atoms that the unit cell intersects
3. the ratio of volume of the atoms in a unit cell to the volume of the unit cell

20. A material is “Amorphous” when:

1. Its structure is not crystalline
2. Its atoms are packed in periodic 3 D arrays
3. Its structure contains numerous defects
4. It forms simple cubic unit cells

21. The solubility of a solute in general

1. decreases when the atomic radii are similar.
2. Increases when the crystalline structure of both solvent and solute is dissimilar
3. Increases when the crystalline structure of both solvent and solute is similar
4. is higher when the atom sizes are very dissimilar

22. Most imperfections in solid crystal structure of metals originate:

1. When it is subjected to stress and strain
2. During the machining process
3. When the material is heated
4. When the molten metals solidify

23. Vacancy diffusion is applicable to

1. Substitutional impur ity atoms
2. Covalently bonded molecules in atomic lattices
3. Atoms present in the interstitial spaces
4. Liquid molecules

24. Interstitial diffusion is:

1. Slower than substitutional diffusion as the small atoms in the interstices do not have enough energy to easily move across the lattices
2. Faster than regular diffusion as it occurs only at higher temperatures
3. Slower than regular diffusion as the larger host atoms offer greater resistance to movement
4. Faster than substitutional diffusion as the small atoms in the interstices have many location to which they can move to.

25. Critical resolved sheer stress is a material property and is

1. twice the magnitude of the yield strength
2. twice the magnitude of the tensile strength
3. one half the magnitude of the yield strength
4. one half the magnitude of the tensile strength