GLARE®
Glare has been chosen for the upper fuselage shell of the A380. The use of Glare results in a weight saving of around 800 kg. In addition to that Airbus is enthusiastic about the proven superior fatigue and damage resistance. The fact that GLARE can be repaired in the same way as standard aluminium is very helpful for the application.
Fibre metal laminates
Fibre-reinforced metal laminates (FML) are hybrid composites consisting of alternating layers of aluminium-alloy sheets and fibre-reinforced epoxy prepreg. The laminates are built up from 0.2 to 0.5 mm thin aluminium alloy sheets bonded into one laminate by intermediate 0.1 to 0.2 mm thin fiber/epoxy layers. The laminates are developed at Delft University of Technology primarily for aircraft structures. The variant with aramid fibers is called ARALL (Aramid Reinforced ALuminium Laminates), while GLARE® (GLAss REinforced) incorporates S2-glass fibers. FML have a high fatigue resistance, achieved by the intact bridging fibres in the wake of the crack, which restrain crack opening.
Controlled delamination in the material enables some crack opening without fibre failure. The laminates can be formed and machined like aluminium alloys and have the high specific strength of composite materials: they combine the best of two worlds. The FML can be stretched after curing in order to reverse the internal stress system in the material. Due to the difference in the thermal expansion coefficients, the as-cured laminate has tensile stresses in the aluminium layers and compressive stresses in the fibre layers. During the stretching operation the aluminium layers deform plastically, while the fibre/epoxy layers remain elastic. Therefore residual stresses are present in the laminate after unloading. After the poststretching operation the laminates have a favourable compressive (crack closing) stress in the aluminium sheets and a tensile stress in the fibres. Several types and lay-ups are commercially available
Fatigue of Fibre metal laminates
Fatigue strength is what fibre metal laminates where designed for, and the do excel in it.
Fire resistance
Due to the layered build up of GLARE® and ARALL® remarkable burn-trough properties
Due to the high melting temperature of the glass fibre (1500 °C) the fibres remained intact, whereas the epoxy burned and formed a carbon layer around the fibres. Delamination of the laminate took place, which caused a very effective insulation as can be seen in the picture.
No flame penetration was observed for Glare after 10 minutes, whereas the 2024-T3 samples showed burn-through within 100 sec at approximately 1150 °C.
Different types of Fibre Metal Laminates
|
grade |
Al alloy |
pre-preg |
orientation |
thickness (mm) |
post stretch |
|
ARALL-1 |
7475-T6 |
aramid-epoxy |
unidirectional |
0.2 - 0.4 |
0.4% |
|
ARALL-2 |
2024-T3 |
aramid-epoxy |
unidirectional |
0.3 - 0.4 |
no |
|
ARALL-3 |
7475-T76 |
aramid-epoxy |
unidirectional |
0.3 - 0.4 |
0.4% |
|
GLARE®-1 |
7475-T76 |
glass-epoxy |
unidirectional |
0.3 - 0.4 |
yes |
|
GLARE®-2 |
2024-T3 |
glass-epoxy |
unidirectional |
0.2 - 0.4 |
no |
|
GLARE®-3 |
2024-T3 |
glass-epoxy |
0o/90o cross-ply |
0.2 - 0.4 |
no |
|
GLARE®-4 |
2024-T3 |
glass-epoxy |
0o/90o/0o cross-ply |
0.2 - 0.5 |
no |
|
GLARE®-5 |
2024-T3 |
glass-epoxy |
0o/90o/90o/0o cross-ply |
0.2 - 0.5 |
no |
The laminates can be applied in various thicknesses, e.g. a 3/2 lay-up means a laminate with three aluminum layers and two intermediate fibre/epoxy layers: [Al/pre-preg/Al/pre-preg/Al]. The fibre/epoxy layers of a 3/2 lay-up can be multiple cross-plied 0/90 layers or can be unidirectional, e.g.: [Al/0°/90°/Al/0°/90°/Al] is a cross-plied lay-up.