J. C. Ehrstrom, T. Crawford, C. Hénon, Alcan, Voreppe, France; D. Hofmann, Alcan NTC, Neuhausen, Switzerland; K. P. Smith, Alcan Rolled Products, Ravenswood, WV
Carbon Fiber Reinforced Plastics (CFRP) were selected for the outer structure of aircraft wing and fuselage of Boeing 787 and Airbus 350. However, CFRP’s perform less well than metals in out of plane directions, so the internal components are often metallic. Aluminum represents a light weight low cost solution, but its electrochemical potential difference with carbon, its higher thermal expansion coefficient and lower Young’s modulus are issues when it is joined to CFRP. A straightforward solution is to use Titanium, which has more compatible properties but associated cost and manufacturing difficulties.
The present paper shows the result of fatigue and corrosion tests that were done on hybrid joints involving an intermediate component bolted onto an Aluminum plate on one side and a CFRP plate on the other side. The intermediate components are Al-Li plate, Titanium plate, Al-Li plate covered with a Kevlar protective layer, Fiber Metal Laminates (FML) and spliced FML/CFRP. Aluminum plates were subjected to a typical surface treatment plus primer coating.
The results of fatigue endurance tests show that bulk metal offer a good performance versus layered materials that crack earlier and are subjected to inter-ply delamination during the compressive part of the fatigue cycle.
Corrosion tests in salt fog show that Titanium/Aluminum joints perform better than direct CFRP/Aluminum joints, despite a relatively similar potential drop. This phenomenon can be linked to the shape of polarization curves implies that the current density is reduced by a factor 10 or more by replacing CFRP with Titanium. The laminates are subjected to strong corrosion when edges are not protected. Bolted joints behave well due to marginal electrolyte ingress. More tests combining load and aggressive environment are needed.
These preliminary tests help to orientate towards reduced cost hybrid solutions that involve largely Aluminum for the internal structures of aircraft.
Summary:
Carbon Fiber Reinforced Plastics (CFRP) were selected for the outer structure of aircraft wing and fuselage of Boeing 787 and Airbus 350. However, CFRP’s perform less well than metals in out of plane directions, so the internal components are often metallic. Aluminum represents a light weight low cost solution, but its electrochemical potential difference with carbon, its higher thermal expansion coefficient and lower Young’s modulus are issues when it is joined to CFRP. A straightforward solution is to use Titanium, which has more compatible properties but associated cost and manufacturing difficulties.
The present paper shows the result of fatigue and corrosion tests that were done on hybrid joints involving an intermediate component bolted onto an Aluminum plate on one side and a CFRP plate on the other side. The intermediate components are Al-Li plate, Titanium plate, Al-Li plate covered with a Kevlar protective layer, Fiber Metal Laminates (FML) and spliced FML/CFRP. Aluminum plates were subjected to a typical surface treatment plus primer coating.
