One of the FML that have been introduced with success is the material Glare.
Glare is a member of a family of materials called Fibre Metal Laminates. Fibre Metal Laminates are materials consisting of thin layers of metal sheet and unidirectional fibre layers embedded in an adhesive system. Glare is an optimised Fibre Metal Laminate for aircraft and it consists of alternating layers of aluminium and glass fibre pregreg layers.
A laminate is produced in an autoclave curing cycle. The different layers of the laminate are stacked before curing by hand lay-up, or by automated machines. Because of the layered structure of the material it is possible to tailor the material for a particular application. Both the number of layers as well as the direction of the fibre layers can be varied depending on the application of the structural part. From the early seventies a lot of work has been performed on the development of Fibre Metal Laminates at Delft University of Technology in order to create a material with improved fatigue properties and high damage tolerance capabilities. This development has amongst others been driven by the accident with a Boeing 737 in which after intensive use many fatigue cracks occurred and a large part of the fuselage separated in flight from the aircraft.
Glare is the successor of the Fibre Metal Laminate type named Arall, which consisted of aluminium sheets and aramid fibre prepreg layers. Glare is improved for aircraft primary and secondary structures.
Up to now seven standard Glare grades have been developed. The number of prepreg layers and their orientation determines the Glare grade. All grades are based on uni-directional glass fibres embedded in Cytec FM 94 structural adhesive. The thickness of the aluminium layers in the Glare laminates ranges from 0.2 to 0.5 mm.
In the table below the six grades are given, including their most important material properties.
|Grade||Sub-grade||Metal sheet thickness [mm] and alloy||Prepreg orientation* in each fibre layer**||Main characteristics|
|Glare 1||0.3 – 0.4 7475-T761||0/0||Fatigue, strength, Yield stress|
|Glare 2||2A||0.2 – 0.5 2024-T3||0/0||Fatigue, strength|
|2B||0.2 – 0.5 2024-T3||90/90||Fatigue, strength|
||3A||0.2 – 0.5 2024-T3||0/90||Fatigue, Impact|
|3B||0.2 – 0.5 2024-T3||90/0|| Fatigue, Impact
|Glare 4||4A||0.2 – 0.5 2024-T3||0/90/0||Fatigue, strength in 0° direction|
|4B||0.2 – 0.5 2024-T3||90/0/90||Fatigue, strength in 90° direction|
||5A||0.2 – 0.5 2024-T3||0/90/90/0|| Impact
|5B||0.2 – 0.5 2024-T3||90/0/0/90|| Impact
|Glare 6||6A||0.2 – 0.5 2024-T3||+45/-45||Shear, off-axis properties|
|6B||0.2 – 0.5 2024-T3||-45/+45||Shear, off-axis properties|
|*||All aluminium rolling directions in standard laminates are in the same orientation; the rolling direction is defined as 0°, the transverse direction is defined as 90°.|
|**||The number of orientations in this column is equal to the number of prepregs (each about 0.125 mm) in each fibre layer.|
A laminate coding system is used to comprehensively define laminates from the table above. An example is: Glare 4B-4/3-0.4
- A Glare laminate with fibre orientation according to the Glare 4B definition in the table above.
- 4 layers of aluminium and 3 fibre layers.
- An aluminium layer thickness of 0.4 mm.