Inge-Innova Aeronautics

1. 2014-09-18
Inge-Innova Aeronautics delivers a fixture for vibration testing of aeronautical components
Inge-Innova Aeronautics develops a turnkey project designing and manufacturing a fixture for vibration testing of aeronautical components
Vibration test fixtures are employed as an ancillary element to facilitate the fixation of the test specimen to the shaker table to properly characterize the specimen, be it a system, subsystem or plainly a unique component of the aircraft.
The design of the fitting is critical in order to avoid errors induced in the prototype dynamic response. The testing machine should transmit the vibration energy regularly and gently through the mass of the auxiliary frame with the slightest energy loss, minimizing the mechanical impedance introduced by an additional element on the system trying to simulate the flight conditions on the specimen. These circumstances are unknown on most of the occasions therefore the design criteria are based on the theory of vibration.
At the design stage the material and dimensions should be chosen taking into account the test restrictions. Parameters such as mass, stiffness, center of gravity and modes and natural frequencies of the fixture will be evaluated and some design guidelines should be followed.
Material selection
These sort of fixtures are made of an aluminum alloy, widely used in aeronautics, that will be selected according to its weldability, more than the mechanical properties because they will deteriorate after welding (HAZ: heat affected zone).
Among other characteristics aluminum alloys are resistant and light at the same time which benefits the equipment performance.
Design
The first consideration is to manufacture a welded fixture, not a bolted one, on account of its rigidity.
Bearing in mind the dimension restrictions, weight limits, dynamic clearance (between specimen and fixture) a coarse model is designed to perform an initial modal analysis

2. and obtain a rough reckoning of the specifications deemed fundamental by the customer.
Once this preliminary prototype is figured out, the design may move on to a second stage in which more details are defined up to the definitive model: specimen-fixture interfaces, tolerances, surface finishing, etc.
Another important part of the design is the connection between the base of the fixture and the shaker table deciding the pattern, dimension and number of fixations so as to allow the energy to be transmitted uniformly without any loss.
So important is also to consider the handling of the fixture just in case lifting lugs were needed or, merely, strapping and securing through the fixture itself could be enough.
Fabrication
An adequate welding method should be chosen and special attention will be paid to the welding sequence so as to prevent distortions that usually occur in every material and, particularly, in aluminum.
A proper welding which involves process and parameters, the welder qualification, welding preparation and tips expressly for aluminum alloys welding will avoid defects leading to an unexpected breaking of the mounting structure.
Should it be necessary, a complete heat treatment would be applied. Distortions may happen after quenching and the part should be straightened before ageing.
Conclusions
Delivering a tailored fixture to the customer according to his specifications, reveals the importance and advantages of the knowledge, not only know but do, combining theory and expertise besides the fact of its applicability in industry. Video