Scalable measurement systems from sensor to software for aircraft fatigue testing
Before the aircraft takes off for the first time, the expected loads of different operating situations are tested in the stand. The aim is to know exactly how the aircraft structure will behave in different situations. Any design flaws must be discovered during these tests to ensure maximum safety in operation.
Aircraft fatigue testing encompasses several specific applications:
Full-scale fatigue tests simulate various operating situations typical for the whole aircraft structure, e.g. landings, take-offs, pressurizing and depressurizing the cabin. For these time-compressed tests, a set of flight types – rough, smooth, emergency landing etc. – is defined and the expected loads are applied. Typically, the tests last a few years to simulate several times the lifetime of the aircraft.
Ultimate load is defined as the limit load of the wing times safety factor: For example 1.5 times the maximum load that the wing is expected to see once during its whole lifetime. During the test, the load is increased in several small steps up to ultimate load. Even at that point, all components of the wing including ailerons and flaps must work correctly. In some cases, load is increased beyond ultimate load until the wing fractures to make sure that it is not too heavily built.
In component tests, the expected loads of multiple times the lifetime of the aircraft are applied to isolated components. This includes doors, wings, empennage etc. Component tests typically replicate the loads of real flights. This ensures that all components by themselves can withstand the expected lifetime loads before they are assembled for the full-scale fatigue test.
Image courtesy of IABG
In aviation, weight is expensive. That is why manufacturers continuously improve the materials used for new aircrafts. The trend goes towards composite materials, additive manufacturing, lighter alloys and ceramics. To test the resilience of these materials, load is applied to single material coupons. The coupons need to withstand cyclic loads, tension, compression, bending and torsion.