Remember that in some cases there is no one correct answer and your score will depend on how well you substantiate your answers. A one sentence explanation is required on True/False questions. If any values are looked up anywhere please cite where you got the value from.
1. This first question deals with basic composite concepts. It contains five parts.
A. True or False. Composites are an exclusive set of advanced materials that by definition must contain a polymeric resin and a continuous fibrous reinforcement.
B. Carbon/epoxy design parameters are typically set by establishing _________ tension and ________ compression properties.
C. Define specific strength and specific modulus.
D. Describe why it might not be a good idea to go into production making wing skins for a commercial transport using a composite tool with a glass transition temperature is 375 °F.
E. Define UHMWPE and give one potential advantage and one potential disadvantage for using the material in an aerospace application.
2. This question deals with the use of composites on Boeing Aircraft.
A. True or False. Boeing has been using Carbon/Epoxy prepregs on its commercial aircraft since the mid 1960's.
B. List the percentage of composite (by weight) utilized on the following planes: 747, 767, 777, and 787.
C. Name three production military aircraft (a bomber, a fighter, and a rotorcraft) for which Boeing was/is a lead or prime contractor that used/uses composites on much of the primary structure.
D. True or False. Boeing is using thermoplastic composites on much the 787's airframe because of lower processing costs.
E. Describe what a hybrid composite is.
3. This question covers some of the basic concepts involved in the manufacture of composite parts.
A. List three forms of incoming composite prepreg and a lay-up method that could be used to place each of the forms.
B. Write a short paragraph (containing at least two concrete arguments) supporting or refuting the following statement. "Filament winding is a low cost rapid method for making large bodies of revolution and therefore is a good candidate process for making composite fuselage barrel sections."
C. Which method, "Injection or Compression Molding" has the potential for making stronger parts? Explain your answer.
D. List four methods for cutting composite prepreg and two methods for trimming cured composite parts.
E. Make a table showing two benefits and two drawbacks for each of the following processes, Wet Lay-up, Oven Cure, and Autoclave Cure.
4. The following question focuses on composite reinforcements.
A. Provide a one sentence definition for each of the following twist, band, and yield?
B. List five carbon fiber modulus categories and a typical tensile range for each.
C. Since SPECTRA has high specific tensile strength and tensile modulus one might think it a good candidate for making aircraft hardware. Write three sentences agreeing with or disagreeing with this statement.
D. If you desire to make a part that has a requirement for high impact resistance over all other criteria and the matrix resin must be a 350F cure epoxy, which of the following fibers would you choose and why? Arimid, Glass or Carbon
E. Describe warp and fill.
5. Material form questions.
A. List 3 types of honeycomb core and state one advantage for each.
B. What does the term "net resin" mean"? Also "neat resin"
C. What type of weave would you use to make a highly contoured part? Why?
D. _________ and_________ reinforcing mats are used extensively in the automotive, industrial, and recreational, industries to make moderately loaded parts.
E. Provide three reasons why you might make a part from dry fiber and neat resin instead of using prepreg.
6. This question deals with preforms.
A. List five types of preforms.
B. Provide two advantages and two disadvantages associated with stitching.
C. True or False. Resin transfer molding and vacuum assisted resin transfer molding usually yield parts that are inherently stronger than hand laid up prepreg.
D. Describe an application where you might use a spray on composite system?
E. List three advantages and three disadvantages of using preforms.
7. This question deals with honeycomb core.
A. Explain the basics of load carrying in a honeycomb core part.
B. Name three reasons why a designer might chose Nomex core over HRP.
C. True or False. There is typically no difference between co-cured honeycomb core panels and bonded face sheet panels. Provide one sentence explaining your answer.
D. Describe foaming adhesives and potting compound as they apply to sandwich panels.
E. Describe "L" and "W" as they apply to honeycomb core.
8. Resin related questions.
A. Describe three differences between thermosets and thermoplastics?
B. Which process VARTM and RTM requires resins with lower viscosity to process? Why?
C. List four primary functions of the matrix resin in a composite laminate.
D. If you were designing a fighter wing that had 425° F use temperatures, what resin system would you use and why?
E. If you were designing a plastic dog house, what resin system would you use and why?
9. Misc. True or false questions,
A. Epoxies resins must be cured at 250° F or preferably 350F to achieve maximum properties.
B. Carbon fibers have high strain to failure capability, typically 4 to 6%.
C. Use temperature for a composite is typically 25° F lower than the glass transition temperature of the matrix resin.
C. Most composites have serious fatigue concerns that must be taken into account when establishing useful life.
D. Manual lay-ups are not as precise as ones made by automated equipment and therefore a structural knockdown must be considered when using them.
10. Misc. fill in the blank,
A. When determining what type of tooling material to use during cure of a part, one should try to match the __________ of the tooling and composite materials.
B. When evaluating material out time one must consider the following lives _________, _________ and ________.
C. Three types of fiber metal laminate are _________, _________ and ________.
D. Provide three common liquid molding acronyms ________, _______ and ________.
E. The following three precursors can be used to make graphite fibers ________, _______ and ________.
1) An interplay hybrid laminate contains 24 layers of GY-70 carbon fiber-epoxy and 15 layers of Kevlar 49 fiber-epoxy. The fiber weight fraction wf in both carbon and Kevlar 49 layers is 60%. Determine:
A. The overall volume fraction of carbon fibers in the laminate and
B. The volume fraction of layers containing carbon fibers
2) Mechanical properties of a carbon epoxy laminate can be affected by the amount of air voids (porosity)in a cured laminate developed during manufacturing. Using the acid digestion method calculate the amount porosity in a cured sample that was taken from the manufacturing excess of a laminate panel. Use the given values below and assume the laminate uses typical IM7 fiber and an epoxy resin properties. Do you expect this method to provide an accurate measure of porosity?
Weight of Empty Crucible = 10.1528g
Weight of crucible + sample before burn-off = 10.5219g
Weight of crucible + sample after burn-off = 10.3221g
Listed Fiber Volume Percent 54%
3) A carbon epoxy composite hollow tube contains 60 volume percent unidirectional AS4 fibers. (Outside diameter = 50mm, wall thickness = 4 mm, and length = 4m). The tube is gripped during testing in a manner as to provide pure tension loading. If the tube was originally changed from a Ti-6A1-4V (aged) titanium alloy design, show that strength to weight ratios are improved with this change by calculating the mass of the (A) composite tube, and (B) the tensile strength and (C) compare specific strength of the composite and Ti tubes. Use the values of a toughened epoxy (Em = 3.6GPa, σmy = 105MPa, and εmu = 3.1%) and typical epoxy density and look up values for a titanium alloy.
1. What are the resulting differences in mechanical properties of pitch-based and PAN-based carbon and graphite fibers?
2. When considering plain weave and satin weave fabrics: (a) which product form has better drapability and why?, (b) which has higher strength and why? and (c) which has smoother surface finish?
3. Name and describe the three main prepregging techniques. Which processes is used to make the majority of prepregs today?
4. What fiber form and type, resin type, product form and processes would you use to create a highly accurate, heavily loaded, small to medium size production aerospace component with good dimensional tolerance and good internal and external surface finish and why?
1. Describe how discrete rubber particle toughening effects delamination growth (interlaminar crack propagation) in fiber-reinforced composite laminates?
2. What resin would you select for an application with a use temperature of 600º F for moderate duration exposure. What is MDA and describe the safety concern? Where are safety concerns explicitly stated in Boeing and Industry documentation.
3. What is "imide corrosion" and how can it be mitigated?
4. Which resin system provides good dimensional stability for space structures and what is the chemical structure that makes this possible?
5. What is gellation, what is the gel point and what test is used to determine the gel point of a resin?
1. How do typical oven cure laminate void contents compare to autoclave cure void contents. What effect does void content have on mechanical properties?
2. How does hydrostatic resin pressure effect final part quality?
3. What effect does moisture have on the cure quality of a composite laminate? How about moisture in honeycomb core prior to cure? How about in parts that are going to be hot bonded using only vacuum pressure.
4. What causes residual cure stresses in composites? What is the stress free temperature?
5. How would you mitigate an exotherm condition during cure?