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Place Room 1Z56 at ENS Paris-Saclay
Non-local approach to fretting-fatigue problems, modelling contact behaviour under complex conditions.
Fretting phenomenon occurs when two contacting solids are subjected to vibratoryloads, resulting in micro-slip at the contact interface. This phenomenon can lead to microcracks initiation and wear debris formation within the contact region. Under the combined action of a fatigue force, micro-cracks initiated by fretting can propagate into contacting parts, leading to an early failure of the structure.
Fretting-fatigue phenomenon is encountered in many industrial applications and is a major concern. In aeronautical industry, fretting-fatigue occurs at blade/disk root attachment zones in aircraft engines and can lead to the failure of a blade or a disk on which cracking is not allowed. This thesis focused on the development and implementation of a calculation chain that can be used in an industrial context to predict fretting-fatigue crack initiation risk through a non-local modeling of the contact zone. This non-local modelling relies on an analogy between contact mechanics and linear elastic fracture mechanics, and enables to take into account efficiently the gradient effect in fretting-fatigue by using non-local variables. First, a new formalism to extend the non-local modelling to the case of elastically dissimilar contacting solids is proposed in this work. In fact, in industrial applications, the bodies in contact are generally made of different materials. Secondly, to compare the predictions of the non-local model with experiment, Safran Aircraft Engines has acquired an experimental setup to carry out fretting-fatigue tests under complex loading conditions. These tests are representative of the fretting-fatigue problems encountered in industrial applications, and provided a basis for the validation of the non-local model. Thus, numerical tools and methods have been develo,ped for the use of the non-local model, firstly on 3D finite element simulations performed by applying the same loading conditions as those imposed during fretting-fatigue experiments. These tools and methods were then applied directly to the fretting-fatigue tests. For this puurpose, the digital image correlation technique is used to extract mechanical fields during the experiments.Finally, analyses revealed that the flexibility of the fretting-fatigue experimental setup allowed for unexpected rotational movements and needed to be taken into account to properly define the boundary conditions in the simulations. To account for this compliance in a numerical model, a digital twin of the experimental setup has been developed to faithfully reproduce numerically the fretting-fatigue tests. A complete implementation of the calculation chain is also carried out on the finite element simulations performed with the digital twin model.
The jury is composed of the following members :
• M. Daniel NELIAS, Professor, INSA de Lyon - Reviewer
• M. Reza TALEMI, Professor, KU Leuven (Belgium) - Reviewer
• Mme Marie-Christine BAIETTO, Research Director at CNRS, INSA de Lyon - Examiner
• M. David NOWELL, Professor, Imperial College of London (UK) - Examiner
• M. David NERON, Professor, ENS Paris-Saclay - Examiner