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Which correctly compares carbon-fiber-reinforced plastic (CFRP) and glass-fiber-reinforced plastic (GFRP)?

  1. AGFRP conducts electricity, so unlike CFRP it readily causes galvanic corrosion when in contact with aluminum alloys
  2. BCFRP is transparent to radio waves and highly insulating, so it is suited to radar covers and electrical insulating parts in place of GFRP
  3. CCFRP excels in specific stiffness but conducts electricity, so it readily causes galvanic corrosion in contact with aluminum alloys
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Answer: C. CFRP excels in specific stiffness but conducts electricity, so it readily causes galvanic corrosion in contact with aluminum alloys

Carbon fiber has a density of about 1.8 g/cm³, lower than glass fiber (about 2.5 g/cm³), and a Young's modulus of about 230 GPa or more, over three times that of glass fiber (about 70 GPa), so CFRP excels in specific stiffness and specific strength and is used in aircraft and sporting goods. However, it is expensive, and because carbon fiber conducts electricity and has a noble electrode potential, contact with aluminum alloys readily causes galvanic corrosion of the aluminum; countermeasures include placing a layer of glass fiber between them. It is CFRP that conducts electricity, not GFRP. Transparency to radio waves and high insulation are characteristics of GFRP, which is used for radomes, electrical insulating parts, and inexpensive boat hulls and bathtubs.

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More Composite materials questions

  1. Which value is closest to the ratio CFRP/steel of the specific modulus (Young's modulus/density) in the fiber direction, for unidirectional CFRP (Young's modulus 140 GPa in the fiber direction, density 1.6 g/cm³) and steel (Young's modulus 210 GPa, density 7.9 g/cm³)?
  2. When a short fiber embedded in a matrix is loaded in tension along its length, which correctly describes the distribution of tensile stress within the fiber? Assume the interface does not slip and transfers load at a constant shear stress.
  3. Which statement about the in-plane stiffness of a laminate in which unidirectional plies are stacked crosswise and symmetrically, as in [0/90]ₛ, is correct?
  4. When glass fibers are used to reinforce a resin, what is the main purpose of treating the fiber surface with a silane coupling agent?
  5. Which correctly describes the properties of a metal matrix composite (MMC) of an aluminum alloy reinforced with SiC particles?