EXPERIMENTAL METHODS AND MEANS
1. Combined loading
The institute has a modular multiaxial beam frame supporting Multi-Instrumented Technology Evaluators. This is a quadripod used to apply loading (6 components) to a specimen having dimensions that are typically of the order of 600 mm by 450 mm for a thickness that can reach 15 mm. This tool is used, for example, for the experimental evaluation of the complex static stress behaviour of a 16-step elliptical step-lap repair. An ASTRID ANR project entitled BLAST is underway to extend the concept of technology evaluator to situations of vulnerability to blast of composite fuselages and to analyse the over-protective behaviour of light armoured floors, considering the manufacturing conditions.
In the framework of the VERTEX collaborative project funded by ANR in which the ICA was the leader, a test bench reproducing the stresses (traction, compression, shear and internal pressure) and the boundary conditions of aeronautical composite structures has been developed. The stresses can reach several thousands of N / mm for a pressure of 1.6 bar with a 400×400 mm² zone of interest. A specific measurement methodology was developed in collaboration with the ICA MICS group. A cluster of 6 cameras allowing for near-field and far-field measurements is used, coupled with a so-called FE-DIC method. The regularization of the finite element optical measurement field allows an improved test / calculation dialogue by the direct export of nodal displacements (translations and / or rotations) to the finite element models.
2. Bonding and Interfaces
Many tests have been developed during recent research works, including an experimental delamination propagation method in mode I and II under gigacyclic fatigue. It is based on the structural resonance of the specimen and allows frequencies up to 400 Hz to be used. An original method of measurement in mode III (Edge Ring Crack Torsion Test (ERCT)) has been proposed and has been extended to the study of mixed modes I + II + III.
3. Measurement Methods and Specific Tests
Other work focuses on continuous monitoring of composite structures at different scales throughout their life cycles. The instrumentation of the structures and, when possible, of their tools and means of production is carried out to find the influence of the various process parameters and materials and the associated variabilities. Bragg optical fibre has allowed residual curing stresses to be studied in the current or singular zone of composite parts and tool-part interactions to be investigated through work for several PhD theses considering different manufacturing processes (autoclaving, filament winding, etc.) and machining (drilling).
A method of analysis by infrared thermography has also been developed to measure energy restitution rates during compression of the carbon plies, among other things. This method has been patented and is the subject of a dissemination action via TTT (Toulouse Tech Transfert).
4. Dynamic testing
[C. Bouvet, O. Dorival, JF. Ferrero, F. Lachaud, S. Marguet, P. Navarro, S. Rivallant]
The Clement Ader Institute, in partnership with Airbus and IRT Saint Exupéry, has developed the “STIMPACT” dynamic testing platform on its premises. The platform has 3 gas guns covering a wide range of impacts up to 2 kg and 800 m/s. The institute also possesses several Drop Towers of up to 5000 J and a new machine provided by Airbus Central R&T is currently being installed. It will enable dynamic materials testing and crash tests of up to 35000 J to be carried out on structural parts.