7.1.3 A Few Remarks The construction using only glass fibers is less and less favored in comparison with a combination of Kevlar fibers and carbon fibers for weight saving reasons: If one would like to have maximum strength,use Kevlar. If one would like to have maximum rigidity,use carbon. Kevlar fibers possess excellent vibration damping resistance. Due to bird impacts,freezing rain,impact from other particles (sand,dirt), one usually avoids the use of composites in the leading edges without metallic protection.3 Carbon/epoxy composite is a good electrical conductor and susceptible to lightning,with the following consequences: Damages at the point of impact:delamination,burning of resin Risk of lightning in attachments (bolts) The necessity to conduct to the mass for the electrical circuits situated under the composite element Remedies consist of the following: Glass fabric in conjunction with a very thin sheet of aluminum (20 um) The use of a protective aluminum film (aluminum flam spray) Temperature is an important parameter that limits the usage of epoxy resins. A few experimental components have been made of bismaleimide resins (ther- mosets that soften'at temperatures higher than 350C rather than 210C for epoxies).One other remedy would be to use a thermoplastic resin with high temperature resistance such as poly-ether-ether-ketone "peek"s that softens at 380C.Laminates made of carbon/peek are more expensive than products made of carbon/epoxy.However,they present good performance at higher operating temperatures (continuously at 130C and periodically at 160C)and have the following additional advantages: ■ Superior impact resistance ■ Negligible moisture absorption Very low smoke generation in case of fire 3The impacts can create internal damages that are invisible from the outside.This can also happen on the wing panels (for example,drop of tools on the panels during fabrication or during maintenance work). 4The mechanical properties of the thermoset resins diminish when the temperature reaches the "glass transition temperature." 5 See section 1.6 for the physical properties. 2003 by CRC Press LLC7.1.3 A Few Remarks The construction using only glass fibers is less and less favored in comparison with a combination of Kevlar fibers and carbon fibers for weight saving reasons:
If one would like to have maximum strength, use Kevlar.
If one would like to have maximum rigidity, use carbon.
Kevlar fibers possess excellent vibration damping resistance.
Due to bird impacts, freezing rain, impact from other particles (sand, dirt), one usually avoids the use of composites in the leading edges without metallic protection.3 Carbon/epoxy composite is a good electrical conductor and susceptible to lightning, with the following consequences:
Damages at the point of impact: delamination, burning of resin
Risk of lightning in attachments (bolts)
The necessity to conduct to the mass for the electrical circuits situated under the composite element Remedies consist of the following:
Glass fabric in conjunction with a very thin sheet of aluminum (20 mm)
The use of a protective aluminum film (aluminum flam spray) Temperature is an important parameter that limits the usage of epoxy resins. A few experimental components have been made of bismaleimide resins (ther￾mosets that soften4 at temperatures higher than 350∞C rather than 210∞C for epoxies). One other remedy would be to use a thermoplastic resin with high temperature resistance such as poly-ether-ether-ketone “peek”5 that softens at 380∞C. Laminates made of carbon/peek are more expensive than products made of carbon/epoxy. However, they present good performance at higher operating temperatures (continuously at 130∞C and periodically at 160∞C) and have the following additional advantages:
Superior impact resistance
Negligible moisture absorption
Very low smoke generation in case of fire 3 The impacts can create internal damages that are invisible from the outside. This can also happen on the wing panels (for example, drop of tools on the panels during fabrication or during maintenance work). 4 The mechanical properties of the thermoset resins diminish when the temperature reaches the “glass transition temperature.” 5 See Section 1.6 for the physical properties. TX846_Frame_C07 Page 138 Monday, November 18, 2002 12:17 PM © 2003 by CRC Press LLC