Techniques d'inspection par ondes guidées ultrasonores d'assemblages brasés dans des réacteurs aéronautiques

Abstract

The aerospace industry has been investigating the generalization of brazed structural assembly, to reduce weight and cost. There is therefore a need to develop a rapid, reliable, and cost-effective inspection technique to ensure the structural quality of these assemblies. The mechanical strength of a brazed assembly is mainly linked to the quantity of brittle phases in its microstructure. Ultrasonic guided waves enable the detection of such defect when a spatiotemporal measurement is used. Besides with that type of waves it is possible to assess complex shape joints. This master thesis focuses on the development of a technique using ultrasonic guided waves to inspect brazed lap joints, which consist of two Inconel 625 plates brazed with BNi-2. Firstly, finite element simulations were performed to simulate the propagation of ultrasonic waves and to optimize the inspection parameters, these simulations have demonstrated the feasibility of this technique to estimate the amount of brittle phases in a brazed assembly. The optimized inspection parameters were the shape of the excitation signal, its center frequency and the direction of excitation. The simulations have shown that ultrasonic wave energy transmitted through the joint, as well as the reflected energy from the joint, were proportional to the amount of brittle phases. Experimental validations were then performed on three distinctive samples with variable amount of brittle phases in the joint. The samples were brazed for different time (1, 60 and 180 minutes). In order to run the experiments with the same method used in the simulations, the measures were implemented on an automated test bench. The experimental parameters were chosen to validate the simulation results. Finally, experimental results were in accordance with simulations and demonstrate the potential of the inspection method.

Date	3 Aug 2016
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Pierre Bélanger (Supervisor) & Philippe Bocher (Co-supervisor)