Questions and Answers - Composites | Aircraft Systems

Questions and Answers - Composites

Study Aid Questions

Fill in the Blanks

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.


TRUE or FALSE

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


Knowledge Application Questions

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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Multiple Choices Questions

1. What is the role of the Matrix component in the composite material?
a. The Matrix is the primary load carrying element
b. The Matrix supports the fibers and bonds them together
c. The Matrix determines the direction that the composite material will be strongest
d. The Matrix is the stacking sequence of the individual composite plies.

2. What do the structural properties such as stiffness, dimensional stability, and strength of a composite laminate depend on?
a. The curing temperature
b. The size of the fibers
c. The stacking sequence of the plies
d. The Matrix

3. In this ply orientation, the plies are stacked in a 0, ‐45, 45 and 90 degrees sequence or in a 0,‐60 and +60 degree sequences. These types of ply orientation simulate the properties of an isotropic material.
a. Bi‐Directional
b. Quasi‐Isotropic
c. Isotropic
d. Unidirectional

4. What is an individual Fiber called?
a. Splice
b. Roving
c. Filament
d. Tape

5. What three terms are commonly used to describe a bundle of filaments?
a. Strands, Tows, Rope
b. Tows, Yarns, Roving
c. Yarns, Strands, Tows
d. Rope, Roving, Splice

6. Unidirectional tape products have which of the following physical properties?
a. High shear strength perpendicular to the fiber direction
b. High compressive strength across the fibers
c. High tensile strength in the fiber direction
d. High shear and compressive strength in the fiber direction

7. Kevlar is DuPont’s trademark name for what type of fibers?
a. Thermoplastics
b. Polyester
c. Carbon
d. Aramid

8. What is the primary disadvantage of Aramid Fibers?
a. Highly susceptible to impact damage
b. Weak in compression
c. Hygroscopic
d. Both b and c

9. If the graphene layers or planes stack with a two dimensional order, the material is defined as:
a. Carbon
b. Graphite
c. Aramid
d. Fiberglass

10. What is required for aircraft carbon fiber parts that are prone to lightening strike?
a. Lightening Rods
b. Strapping to non‐conductive aircraft parts
c. Alternating aluminum plies
d. Lightening protection mesh or coating

11. What are Ceramic fibers used for on aircraft?
a. Propellers
b. Turbine blades
c. Compressor Blades
d. Exhaust Nozzles

12. What cure temperature do Polyamides require?
a. High cure temperatures in excess of 350 Degrees Fahrenheit
b. High cure temperatures in excess of 450 Degrees Fahrenheit
c. High cure temperatures in excess of 550 Degrees Fahrenheit
d. High cure temperatures in excess of 650 Degrees Fahrenheit

13. Where are Bismaleimide (BMI) resins used?
a. Aero engines
b. High temperature components
c. Control surfaces
d. Both a and b

14. Most honeycomb materials are ; that is, properties are directional.
a. Anisotropic
b. Isotropic
c. Quasi‐isotropic
d. Heterogeneous

15. Honeycomb core cells for aerospace applications are typically what shape?
a. Pentagons
b. Diamonds
c. Octagons
d. Hexagons

16. What shape are honeycomb over‐expanded core cells?
a. Pentagons
b. Hexagons
c. Rectangles
d. Octagons

17. What is considered to be the optimal fiber to resin ratio?
a. 40:60
b. 60:40
c. 70:30
d. 30:70

18. What causes delaminations to form?
a. Matrix cracks that grow into the interlaminar layer
b. Low energy impact
c. Production non‐adhesion along the bond line
d. All of the Above

19. What type of inspection is the primary method for in‐service inspections of composite materials?
a. Audible Sonic Testing
b. Visual
c. Automated Tap Testing
d. Ultrasonic

20. On what type of composite structure is tap testing most effective?
a. Thin skin to stiffer bond lines
b. Honeycomb sandwich with thin face sheets
c. Near the surface of thick laminates
d. All of the above

21. What Ultrasonic Inspection method uses two transducers, one on each side of the area to be inspected?
a. Through Transmission
b. Pulse Echo
c. Ultrasonic Bond tester
d. Phased Array

22. What Ultrasonic Inspection method uses a single search unit as a transmitting and receiving transducer that is excited by high voltage pulses?
a. Through Transmission
b. Pulse Echo
c. Ultrasonic Bond tester
d. Phased Array

23. What type of inspection is the primary method for in‐service inspections of composite materials?
a. Audible Sonic Testing
b. Visual
c. Automated Tap Testing
d. Ultrasonic

24. What is the typical storage life for prepreg material?
a. 2 to 8 months
b. 4 to 10 months
c. 6 to 12 months
d. 8 to 14 months

25. What is used to improve the peel strength of Co‐bonded assemblies?
a. Boron Prepreg tape
b. Film Adhesive
c. Silicon Adhesive
d. Enhanced Epoxy resin

26. What is considered to be a permanent repair?

a. Meet the strength requirements but is limited by time of flight cycles
b. Meet the strength requirements but has a different inspection schedule
c. Meet the strength requirements and the durability requirements
d. b and c are correct

27. A potted repair should not be used for?
a. Small repairs to honey comb structure
b. Small repairs to honey comb engine cowlings
c. Small repairs to honey comb flight controls
d. Small repairs to honey comb spoilers

28. Scarf type repairs use scarf angles to ease the load into the repair.
a. large
b. small
c. scarf angle does not affect the load
d. depends on the repair material

29. What condition could affect the signal of the aircraft radar?
a. Trapped water in the aircraft radome
b. Large potted repairs of the aircraft radome
c. a and b are both correct
d. a and b are both wrong

30. Honeycomb sandwich structures are often repaired with
a. Scarf type bonded repair
b. Scarf type bolted repair
c. An external bolted repair
d. An internal bonded repair


ANSWERS