Questions – Advanced Composites Materials

1. What are the three primary advantages of composite materials?
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2. Name five applications of composites on aircraft.
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3. List the two major components of a laminate.
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4. List four examples of honey comb structures on aircraft.
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5. List four advantages of Thermoplastic honeycomb material.
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6. What are two advantages to using Polystyrene in sandwich structures?
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7. List four composite manufacturing defects.
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8. List four sources of composite manufacturing defects.
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9. Matrix cracks, or micro cracks, can significantly reduce properties dependant on the resin or the fiber/resin interface, such as ________ and ________.

10. List three types of damage to the composite surface that is detectable via a visual inspection.
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11. List four types of discrepancies that can be detected with a visual inspection.
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12. The signal from an unflawed region is used for ________, and any deviation from this unflawed signal (period) indicates the existence of ________.

13. List four contaminants that prepreg materials must be protected from.
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14. ________ utilizes precured composite detail parts, and uses a layer of adhesive to bond two procured composite parts.

15. Precured laminates undergoing secondary bonding usually have a thin ________ or ________ peel ply cured onto the bonding surface.

16. List 3 advantages of using composite doublers to repair metal skin components.
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17. List the four types of bleed out techniques.
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18. A temporary repair must meet the ________ but is limited by time or flight cycles.

19. A ________ repair can be used to repair damage to a sandwich honeycomb structure.

20. Water in the honeycomb core could ________ at high altitudes.

21. Sold laminate structures have ________ plies than the face sheets of honeycomb structures.

22. Resin injection repairs are used on ________ structures for ________ damages to a solid laminate.

23. Aircraft radomes are made of ________ material.

24. The properties of a ________ repair are not as good as a repair with ________ material, but by using a ________ method the properties of a ________ can be improved.

25. The disadvantage of bonded repairs is that most repair materials require ________, and ________ procedures.

26. Bolted repairs are not desirable for ________ structure due to the thin face sheets that have limited ________ strength.

27. Most composite primary structures for the aircraft industry are fastened ________ with or ________ fasteners.

28. Drill bits used for carbon fiber and fiber glass are made from ________ material or ________ because the fibers are so hard that ________ drill bits will not last very long.

29. Countersinking a composite structure is required when ________ fasteners are used.

30. Drilling in composite material require ________ speeds and ________ feeds than drilling in metallic structures.

1. Composite materials consist of a combination of materials that are mixed together to achieve specific structural properties. TRUE/FALSE

2. The Fibers in a composite are the primary load carrying element of the composite material. TRUE/FALSE

3. Kevlar yarns are twisted, while Fiberglass yarns are not. TRUE/FALSE

4. Unidirectional Tape Fibers are held in place by stitching with fine yards or threads and have a higher strength than woven fabrics. TRUE/FALSE

5. Satin Weaves have less crimp and are easier to distort than a plain weave. TRUE/FALSE

6. Special scissors are needed to cut Aramid Fibers. TRUE/FALSE

7. If the graphene layers or planes stack with 3 dimensional order, the material is defined as graphite. TRUE/FALSE

8. Carbon Fibers have a low potential for causing galvanic corrosion when used with metallic fasteners and structures. TRUE/FALSE

9. Thermoplastic materials can repeatedly be softened by an increase of temperature and hardened by a decrease in temperature. TRUE/FALSE

10. Sandwich construction has high bending stiffness at minimal weight in comparison to aluminum and composite laminate construction. TRUE/FALSE

11. Aluminum has the best strength‐to‐weight ration and energy absorption of all the materials used for honeycomb. TRUE/FALSE

12. Bisected hexagonal honeycomb is stiffer and stronger than hexagonal core. TRUE/FALSE

13. Aircraft grade Polystyrene has a tight closed cell structure with no voids between the cells. TRUE/FALSE

14. Matrix imperfections may develop into delimitations, which are a more critical type of damage. TRUE/FALSE

15. Visual inspections can not find internal flaws in the composite, such as delaminations, disbands, and matrix crazing. TRUE/FALSE

16. When performing an Audible Sonic Test, the tapping rate needs to be slow enough to produce enough sound such that any difference in sound tone is discernable to the ear. TRUE/FALSE

17. When using the Through Transmission Ultrasonic inspection method, areas without a signal loss compared to the reference standard indicate a defective area. TRUE/FALSE

18. The mechanical life is shorter than the handling life. TRUE/FALSE

19. Adhesive film is frequently placed into the interface between the stiffener and the skin to increase fatigue and peel resistance. TRUE/FALSE

20. Composite Materials can be used to structurally repair, restore, or enhance aluminum, steel, and titanium components. TRUE/FALSE

21. Too many bleeder plies can result in a resin rich repair. TRUE/FALSE

22. Many high strength prepreg materials in use today are no‐bleed systems. TRUE/FALSE

23. Potted repairs do not restore the full strength of the part. TRUE/FALSE

24. Water or moisture in honeycomb structures does not affect the structure during repair. TRUE/FALSE

25. A scarf repair is more efficiently in load transfer than an external bonded patches. TRUE/FALSE

26. Aircraft radomes are made of at least 10 plies of Kevlar. TRUE/FALSE

27. The double Vacuum Debulk process will improve properties of a wet lay up repair. TRUE/FALSE

28. Bonded repairs are quicker and easier to carry out than bolted repairs. TRUE/FALSE

29. Titanium or stainless steel fasteners are used for bolted repairs of carbon fiber structure. TRUE/FALSE

30. Sickle shaped Klenk drills are used to drill carbon fiber. TRUE/FALSE

1. Describe the term Homogeneous as it applies to laminate structures.

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2. Describe the term Anisotropic as it applies to laminate structures.
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3. Describe the term Quasi‐isotropic as it applies to laminate structures:
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4. What benefit do most fabric constructions offer that straight unidirectional tapes do not?
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5. What is a benefit of tightly woven fabrics on aerospace structures?
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6. Name one type of conductive material used to protect composite components against lightening strikes?
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7. Why are Phenolic resins used for interior components?
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8. How many stages are there to curing resins and what are they?
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9. Briefly explain why prepreg materials must be kept in a freezer at zero degrees Fahrenheit.
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10. Bell shaped core cells, or flexicore, is used for what applications?
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11. Explain what the benefits are for using honeycomb with a high density and small core cells.
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12. Describe what it means for a part to be resin rich.
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13. Describe what it means for a part to be resin starved.
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14. Briefly explain the Audible Sonic Testing method.
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15. Describe the sound indicative of a well‐bonded solid structure when utilizing the Audible Sonic Testing method.
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16. Describe the sound indicative of a discrepant area when utilizing the Audible Sonic Testing Method.
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17. Describe what could produce a faulty result when utilizing the Audible sonic test.
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18. Briefly describe how the Through Transmission Ultrasonic inspection method works.
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19. If a clean room is not available for prepreg material lay‐up, what techniques are used to prevent contamination?
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20. What is co‐curing and describe a typical co‐cure application?
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21. What is the difference between a permanent repair and an interim repair?
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22. What is the restriction of potted repair related to flight controls?
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23. Why does water/moisture needs to be removed before a repair to a honeycomb part is cured?
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24. Explain the resin injection repair method.
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25. Describe why aircraft radomes need to be made of only 3 or 4 plies of fiberglass.
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26. Describe in detail the Double Vacuum Debulk repair process.
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1. Sandwich panels made of metal honeycomb construction are used on modern aircraft because this type of construction

a. may be repaired by gluing replacement skin to the inner core material with thermoplastic resin.

b. has a high strength to weight ratio.
c. is lighter than single sheet skin of the same strength and is more corrosion resistant.

2. (1) When performing a ring (coin tap) test on composite structures, a change in sound may be due to damage or to transition to a different internal structure.
(2) The extent of separation damage in composite structures is most accurately measured by a ring (coin tap) test.

Regarding the above statements,
a. only No. 1 is true.
b. only No. 2 is true.
c. both No. 1 and No. 2 are true.

3. Which of these methods may be used to inspect fiberglass/honeycomb structures for entrapped water?
1. Acoustic emission monitoring
2. X-ray
3. Backlighting

a. 1 and 2
b. 2 and 3
c. 1 and 3

4. When balsa wood is used to replace a damaged honeycomb core, the plug should be cut so that
a. the grain is perpendicular to the skin.
b. the grain is parallel to the skin.
c. it is about 118-inch undersize to allow sufficient bonding material to be applied.

5. When repairing puncture type damage of a metal faced laminated honeycomb panel, the edges of the doubler should be tapered to
a. whatever is desired for a neat, clean appearance.
b. 100 times the thickness of the metal.
c. two times the thickness of the metal.

6. One of the best ways to assure that a properly prepared batch of matrix resin has been achieved is to
a. perform a chemical composition analysis.
b. have mixed enough for a test sample.
c. test the viscosity of the resin immediately after mixing.

7. Composite inspections conducted by means of acoustic emission monitoring
a. pick up the “noise” of corrosion or other deterioration occurring.
b. create sonogram pictures of the areas being inspected.
c. analyze ultrasonic signals transmitted into the parts being inspected.

8. What precaution, if any, should be taken to prevent corrosion inside a repaired metal honeycomb structure?
a. Prime the repair with a corrosion inhibitor and seal from the atmosphere.
b. Paint the outside area with several coats of exterior paint.
c. None. Honeycomb is usually made from a man made or fibrous material which is not susceptible to corrosion.

9. One method of inspecting a laminated fiberglass structure that has been subjected to damage is to
a. strip the damaged area of all paint and shine a strong light through the structure.
b. use an eddy current probe on both sides of the damaged area.
c. use dye penetrant inspection procedures, exposing the entire damaged area to the penetrant solution.

10. When inspecting a composite panel using the ring test/tapping method, a dull thud may indicate
a. separation of the laminates.
b. an area of too much matrix between fiber layers.
c. less than full strength curing of the matrix.

11. How many of the following are benefits of using microballoons when making repairs to laminated honeycomb panels?
1. Greater concentrations of resin in edges and comers.
2. Improved strength to weight
3. Less density.
4. Lower stress concentrations.

a. Three
b. Four
c -Two

12. The length of time that a catalyzed resin will remain in a workable state is called the
A – pot life
B – service life
C – shelf life

13. A category of plastic material that is capable of softening or flowing when reheated is described as a
a. thermoset
b. thermoplastic
c. thermocure

14. The classification for high tensile strength fiberglass used in aircraft structures is
a. S
b. G
c. E

15. Which is an identifying characteristic of acrylic plastics?
a. Zinc chloride will have no effect.
b. Has a yellowish tint when viewed from the edge.
c. Acetone will soften plastic, but will not change its color.

16. Superficial scars, scratches, surface abrasion, or rain erosion on fiberglass laminates can generally be repaired by applying
a. a piece of resin impregnated glass fabric facing.
b. one or more coats of suitable resin (room temperature catalyzed) to the surface.
c. a sheet of polyethylene over the abraded surface and one or more coats of resin cured with infrared heat lamps.

17. The classification for fiberglass reinforcement material that has high resistivity and is the most common is
a. E
b. G
c. S

18. A potted compound repair on honeycomb can usually be made on damages less than
a. 2 inches in diameter
b. 1 inch in diameter
c. 4 inches in diameter

19. Composite fabric material is considered to be the strongest in what direction?
a. Fill
b. Bias
c. Warp

20. What reference tool is used to determine how the fiber is to be oriented for a particular ply of fabric?
a. Fill clock (or compass)
b. Bias clock (or compass)
c. Warp clock (or compass)

21. The strength and stiffness of a properly constructed composite buildup depends primarily on
a. the orientation of the plies to the load direction.
b. the ability of the fibers to transfer stress to the matrix.
c. a 60 percent matrix to 40 percent fiber ratio.

22. Which fiber to resin (percent) ratio for advanced composite wet lay-ups is generally considered the best for strength?
a. 60:40
b. 40:60
c. 50:50

23. What is the material layer used within the vacuum bag pressure system to absorb excess resin during curing called?
a. Release
b. Bleeder
c. Breather

24. Proper pre-preg composite lay-up curing is generally accomplished by
1. applying external heat.
2. room temperature exposure.
3. adding a catalyst or curing agent to the resin.
4. applying pressure.

a. 1 and 4.
b. 2 and 3.
c. 1, 3, and 4.

25. When repairing large, flat surfaces with polyester resins, warping of the surface is likely to occur. One method of reducing the amount of warpage is to
a. use less catalyst than normal so the repair will be more flexible.
b. add an extra amount of catalyst to the resin.
c. use short strips of fiberglass in the bonded repair.

26. When making repairs to fiberglass, cleaning of the area to be repaired is essential for a good bond. The final cleaning should be made using
a. MEK (methyl ethyl ketone).
b. a thixotropic agent.
c. soap, water, and a scrub brush.

27. When necessary, what type of cutting fluid is usually acceptable for machining composite laminates?
a. Water only.
b. Water displacing oil.
c. Water soluble oil.

28. Fiberglass laminate damage not exceeding the first layer or ply can be repaired by
a. sanding the damaged area until aerodynamic smoothness is obtained.
b. trimming the rough edges and sealing with paint.
c. filling with a putty consisting of a compatible resin and clean, short glass fibers.

29. Fiberglass damage that extends completely through a laminated sandwich structure
a. must be filled with resin to eliminate dangerous stress concentrations.
b. may be repaired.
c. may be filled with putty which is compatible with resin.

30. Fiberglass laminate damage that extends completely through one facing and into the core
a. requires the replacement of the damaged core and facing.
b. can be repaired by using a typical metal facing patch.
c. cannot be repaired.

31. Repairing advanced composites using materials and techniques traditionally used for fiberglass repairs is likely to result in
a. an unairworthy repair.
b. improved wear resistance to the structure.
c. restored strength and flexibility.

32. The preferred way to make permanent repairs on composites is by
a. bonding on metal or cured composite patches.
b. riveting on metal or cured composite patches.
c. laminating on new repair plies.

33. Which of the following, when added to wet resins, provide strength for the repair of damaged fastener holes in composite panels?
1. Microballoons
2. Flox
3. Chopped fibers

a. 1 and 3
b. 1, 2, and 3
c. 2 and 3

34. The part of a replacement honeycomb core that must line up with the adjacent original is the
a. cell edge
b. cell side
c. ribbon direction

35. Which of the following are generally characteristic of aramid fiber (Kevlar) composites?
1. High tensile strength
2. Flexibility
3. Stiffness
4. Corrosive effect in contact with aluminum
5. Ability to conduct electricity

a. 1, 3, and 5
b. 1 and 2
c. 2, 3 and 4

36. Which of the following are generally characteristic of carbon/graphite fiber composites?
1. Flexibility
2. Stiffness
3. High compressive strength
4. Corrosive effect in contact with aluminum
5. Ability to conduct electricity

a. 1, 3, and 5
b. 2, 3, and 4
c. 1 and 3

37. If an aircraft’s transparent plastic enclosures exhibit fine cracks which may extend in a network over or under the surface or through the plastic, the plastic is said to be
a. brinelling
b. hazing
c. crazing

38. When installing transparent plastic enclosures which are retained by bolts extending through the plastic material and self-locking nuts, the nuts should be
a. tightened to a firm fit, then backed off one full turn.
b. tightened to a firm fit, plus one full turn.
c. tightened to a firm fit.

39. Which is considered good practice concerning the installation of acrylic plastics?
a. When rivets are used, adequate spacer or other satisfactory means to prevent excessive tightening of the frame to the plastic should be provided.
b. When rivets or nuts and bolts are used, slotted holes are not recommended.
c. When nuts and bolts are used, the plastic should be installed hot and tightened to a firm fit before the plastic cools.

40. The coefficient of expansion of most plastic enclosure materials is
a. greater than steel but less than aluminum.
b. greater than both steel and aluminum.
c. less than either steel or aluminum.

41. If no scratches are visible after transparent plastic enclosure materials have been cleaned, their surfaces should be
a. covered with a thin coat of wax.
b. buffed with a clean, soft, dry cloth.
c. polished with rubbing compound applied with a damp cloth.

42. What is the most common method of cementing transparent plastics?
a. Bevel method
b. Soak method
c. Heat method

43. When holes are drilled completely through Plexiglas, a
a. wood drill should be used.
b. standard twist drill should be used.
c. specially modified twist drill should be used.

44. What is the purpose of a gusset or gusset plate used in the construction and repair of aircraft structures?
a. To join and reinforce intersecting structural members.
b. To provide access for inspection of structural attachments.
c. To hold structural members in position temporarily until the permanent attachment has been completed.

45. What is the typical storage life for prepreg material?

a. 4 to 10 months
b. 6 to 12 months
c. 8 to 14 months

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Answer key