What is FML?
It was more than thirty years ago when FML was developed. FML or Fiber Metal Laminates are the recent kind of composite, which Delft University of Technology developed. The new composite is developed with alternating sheets of aluminum and the conventional composite. The original FML was made up of aramid/epoxy combined with aluminum. It was called the Arall. The product seemed so promising. However, the aerospace trade did not adopt the technology well for some reasons.

Since the aerospace industry was slow in adopting the Arall FML, Delft began to develop a new FML in the 1980s. The new FML was called Glare and it was a glass/epoxy combination. Glare is developed for the use on structures of aircrafts. Researches made have proven that the new composite was a better alternative for aluminum and fiberglass. Glare was proven tougher than the preceding composites and handles intense impact and fatigue very well.

The development of Glare took years before the aircraft industry has finally decided to use it. The Airbus used Glare as a material for the structure of their A380 aircraft. Since the beginning, Delft develops Glare for aircraft structure purposes so that means that the FML was certainly an aircraft material. However, the new FML must complete certain certification before the aircraft industry use it.

In some point, developers knew about the required certification. Therefore, developers published a book entitled ‘Fiber Metal Laminates: An Introduction’. The book is a monograph, which was brought out at a Glare conference in September 2001. Delft included technical papers derived from conferences and sections, which are written exclusively for the FML: AI book. The book is written by several authors but appeared as if it was a unified work.

How did the development of Glare start?

Just like the development of other products, it all begins in the analysis. Using the Metal Volume Fraction or MVD method, the analysis of the Glare development begins. MVF is comparable to the traditional composites’ rule of mixtures. Each material is carefully scrutinized for distinct and useful properties. After analyzing and determining the properties of each material, further testing is done.

Materials will undergo further testing such as blunt notch, stress-strain, fatigue behavior and stability tests. Such tests are essential since the product must achieve certain certification. Experimental data are properly recorded to serve as reference and to extend the theoretical coverage. Documentations are indispensable since Glare is intended for aircraft industry use.

To be able to be considered certified for aircraft structures, a material must be proven safe and tough. Using the book FML: AI, Glare has provided enough documentation of its worth. Delft showed how Glare can be utilized for the design of particular aircraft structures. Documentation provided enough details on how Glare can be applied to such complex structures. Delft did not rely on analytical methods, but did intense testing. Moreover, methods of production were also provided by Delft. The developers of Glare provided actual tests in the context of a real aircraft. They did not rely alone on test panels.

The adoption of Glare in the aircraft industry opened up ideas on how the new FML can be utilized in other areas. Engineers, especially those who are into structure designs may find other important use of Glare in the near future.