Numerical modeling of wear in smooth conformal contact joints

One of Safran's major challenges is to develop Aircraft engines that comply with the safety recommendations issued by certification authorities. In particular, the sizing of the mechanisms is based on the need to achieve good mechanical strength under normal and extreme loads. To design stators without conservatism, and to predict maintenance levels, more predictive mechanical tools are essential. The purpose of the VSV system is to orientate rectifier blades according to aerodynamic specifications. Although the system's function is relatively simple, the design of these mechanisms is made complex by the number of components to be oriented, by the desire to limit the number of actuators and by the need to find compromises between the mass and stiffness of the parts, between low friction and high resistance of the parts, and so on. To limit friction and avoid direct wear on major parts, guiding elements between the housing and the rectifier blades are commonly used. These guiding elements - bushes or plain bearings - are subject to mechanical stresses during assembly and operation. Bushing wear is a major source of high maintenance costs and multiple technical problems. Excessive bushing wear can lead to contact between rotor and stator (rectifier spillage), over-stressing of rectifiers leading to blade cracking, or pumping phenomena. As the time between shop visits increases, the criticality of bushing wear becomes more important. In a previous thesis carried out at the LMPS in collaboration with Safran Aircraft Engines, an initial numerical model was developed for predicting bushing wear in VSV systems. This model provides an estimate of bushing wear under test-bench operating conditions, with computation times appropriate for pre-sizing research needs. This previous research provides an important theoretical basis for a complete resolution of the wear problem, taking into account various aspects that have so far remained unaddressed. The main objectives of this new thesis are to improve the existing model (by taking into account the deformation of assembled parts, improving contact behavior and taking temperature into account, etc.), and to identify/recalibrate and validate the model using test results from Safran Aircraft Engines' semi-technological test benches. The project also includes the transfer of developments carried out at Safran Aircraft Engines, in particular for the development of simulation and sizing tools. It is also envisaged to implement the wear bushing model as a user element within a finite element calculation code for assembly calculations on global VSV engines.

Doctoral Researcher: Vivien Fouquet

Scientific Advisors: Pierre-Alain Guidault, François Louf, Pierre-Alain Boucard