cap 5 Materiales

Question 1

1. Plastics that soften with increasing temperature and regain rigidity as the temperature is decreased are called:

a. thermosetting.
b. thermoplastic.
c. electro-setting.
d. electro-plastic.

Answer 1

b. thermoplastic.

Question 2

2. Plastic materials that cannot be returned to their original state after they have been exposed to higher temperatures during the manufacturing process are referred to as:

a. thermosetting.
b. thermoplastic.
c. electro-setting.
d. electro-plastic

Answer 2

a. thermosetting.

Question 3

3. The greatest variety of plastics comprises:

a. natural materials.
b. rubber-based materials.
c. synthetic materials.
d. fiber-based materials.

Answer 3

c. synthetic materials.

Question 4

4. The most important area of plastic processing is:

a. green sand molding.
b. matched die molding.
c. casting.
d. extrusión.

Answer 4

b. matched die molding.

Question 5

5. Compression molding, cold molding, transfer molding, and injection molding are all examples of what type of plastic processing?

a. Green sand molding.
b. Lost wax molding.
c. Extrusión.
d. Matched die molding

Answer 5

d. Matched die molding

Question 6

6. __________materials may be held in the softened condition for prolonged periods of time with little or no chemical change.

a. Thermosetting
b. Thermoplastic
c. Cryosetting
d. Cryoplastic

Answer 6

b. Thermoplastic

Question 7

7. The high pressures required by compression molding, together with the low viscosity of most thermosetting materials, require that the mold halves have fitting clearances on the order of:

a. 0.025 mm (0.001 in.).
b. 0.0025 mm (0.0001 in.).
c. 0.25 mm (0.01 in.).
d. 2.5 mm (0.1 in.).

Answer 7

a. 0.025 mm (0.001 in.).

Question 8

8. The sprue and runner system, or “cull.” that is produced during the transfer molding process:

a. must be removed and can be reused.
b. must be removed and cannot be reused.
c. is usually designed to form a second part of the product.
d. is usually designed to be an integral part of
the product.

Answer 8

b. must be removed and cannot be reused.

Question 9

9. The injection molding process for thermosetting plastics is referred to as:

a. injection molding.
b. pressure molding.
c. jet, flow, or offset molding.
d. low temperature molding.

Answer 9

c. jet, flow, or offset molding.

Question 10

10. A low tooling cost procedure restricted to thermosetting resins used for low production of jewelry, novelty items, laboratory specimens, and similar parts is called:

a. green sand molding.
b. matched die molding.
c. extrusión.
d. casting of plastics.

Answer 10

d. casting of plastics.

Question 11

11. Thin plastic film is produced either by extruding the plastic through a slit of the appropriate size or by:

a. the expanded tube method.
b. floating the plastic on a large water-cooled drum.
c. blow molding with controlled pressure nozzles.
d. running sheet plastic through progressively
tighter rolls.

Answer 11

a. the expanded tube method.

Question 12

12. Vacuum bag, expanded bag, and autoclave molding are all methods for developing some pressure on the surface of the molding to permit a low resin-to-filler ratio. These are all variations of which type of reinforced plastic molding technique?

a. Compression process.
b. Pressure molding.
c. Contact layup.
d. Molded layup.

Answer 12

c. Contact layup.

Question 13

13. The strength of concrete increases with time. Solidity may occur from a few hours to a few days, but what is defined as 100% strength requires_______.

a. 3 days.
b. 7 days.
c. 14 days.
d. 28 days.

Answer 13

d. 28 days.

Question 14

14. Engineered material consisting of one or more reinforcing agents and a matrix binder acting together as a physical unit while retaining their identities describes what type of material
    a. Woven.
    b. Mixed media.
    c. Conglomerate.
    d. Composite.

Answer 14

d. Composite.

Question 15

15. Tension, compression, torsion, shear, and bending are all examples of:

a. material properties.
b. stress modes.
c. defect factors.
d. construction discontinuities.

Answer 15

b. stress modes.

Question 16

16. The proper performance of an adhesive requires bonding, surface cleanliness, and_______as a minimum.

a. heat
b. pressure
c. intimate contact
d. time

Answer 16

c. intimate contact

Question 17

17. Synthetic fiber in a random assortment of fixed length, or chopped random length fiber yarns that are bound together on a flat mat describes:

a. continuous fiber.
b. discontinuous fiber.
c. two-dimensional woven cloth.
d. three-dimensional woven cloth.

Answer 17

b. discontinuous fiber.

Question 18

18. Fiber used as reinforcement for very high temperature applications is known as:

a. glass fiber.
b. aramid fiber.
c. carbon fiber.
d. ceramic fiber.

Answer 18

d. ceramic fiber.

Question 19

19. The most common fiber used for composites (90%), because of its high tensile strength and its resistance to heat, fire, moisture, and chemicals is:

a. glass fiber.
b. aramid fiber.
c. carbon fiber.
d. ceramic fiber.

Question 20

20. Fiber used as reinforcement, which exhibits
    extreme tensile strength, impact resistance, and
    vibration dampening is known as:

a. glass fiber.
b. aramid fiber.
c. carbon fiber.
d. ceramic fiber.

Answer 20

b. aramid fiber.

Question 21

21. Fiber used as reinforcement, which has very high tensile strength and makes very stiff, lightweight structures and also has very high compressive strength and a negative coefficient of thermal expansion is known as:

a. glass fiber.
b. aramid fiber.
c. carbon fiber.
d. ceramic fiber.

Answer 21

c. carbon fiber.

Question 22

22. Chemically, plastics are all polymers. The smallest unit structure or molecule that identifies the chemical involved is called a(n):

a. isomer.
b. isopolymer.
c. monomer.
d. dipolymer.

Answer 22

c. monomer.

Question 23

23. Drawn filaments of which material may have a tensile strength of 345 MPa (50 000 psi), which is actually greater than some low-strength steels?

a. Acrylic.
b. Nylon.
c. Vinyl.
d. Cellulose nitrate.

Answer 23

b. Nylon.

Question 24

24. The basic steps of primary fabrication of continuous fiber composites are layup and:

a. winding.
b. wrapping.
c. spinning.
d. curing.

Answer 24

d. curing.

Question 25

25. In a good adhesive bond:
    a. adhesion forces and cohesion forces are equal.
    b. adhesion forces always exceed cohesion forces.
    c. cohesion forces always exceed adhesion forces.
    d. cohesion forces are not considered in bonding.

Answer 25

b. adhesion forces always exceed cohesion forces.

Question 26

26. Damage to a composite structure that occurs
    without visual indications at the surface is classified as what type of damage?

a. Structural damage.
b. Superficial damage.
c. Low-velocity impact damage.
d. High-velocity impact damage.

Answer 26

c. Low-velocity impact damage.

Question 27

27. In a low-velocity impact, the most critical damage mechanism in composites is:
    a. fiber pull out.
    b. fiber breakage.
    c. matrix cracking.
    d. delamination.

Answer 27

d. delamination.

Question 28

28. What kind of damage is created by factors such
    as temperature, water pressure, corrosion, erosion, and fire?
    a. Structural.
    b. Mechanical.
    c. Environmental.
    cl Chemical.

Answer 28

c. Environmental.

Question 29

29. Damage assessment comprises three distinct
    steps: discontinuity detection/location, discontinuity assessment. and:

a. discontinuity removal.
b. discontinuity removal assessment.
c. engineering evaluation.
d. discontinuity tolerance assessment.

Answer 29

b. discontinuity removal assessment.

Question 30

30. Maintenance manuals for composite material
    repair normally provide limits (for example, damage size, weight, balance, and repair proximity) based on the criticality of specific parts. In cases where no specific instructions are available or cannot be followed, who makes the repair decision?

a. The maintenance technician performing the work.
b. The maintenance supervisor.
c. The responsible Level Ill.
d. The responsible engineering authority.

Answer 30

d. The responsible engineering authority.