ADVENTURE

The aim of ADVENTURE is to study the influence of overloads in order to build predictive models to handle even short 3D fatigue cracks with a complexity and history effect similar to those encountered in real structures. Reliable models are essential in any industry where cracking is a safety issue. The relationship between crack growth rate before overload and Stress Intensity Factor (SIF) fails. Even if the phenomenon is known, the mechanisms remain controversial and, often, studied on the surface. An understanding of the 3D effects resulting from the variation in size of the plastic zone along the crack front requires further experimental techniques. Coupling fatigue tests under synchrotron tomography with digital volume correlation (DVC) will make it possible to measure the deformations and their evolution after overload. To obtain a high resolution of the DVC, a fine-grained Al-Si alloy with a natural speckle will be fabricated. 2D tests will allow to enlarge the experimental database. The 2D and 3D data (displacement fields, cracks), which are unique at this scale, will feed a new Generalized Incremental (as well as plasticity) crack propagation Model (GIM) that breaks away from the Paris law. The crack propagation rate being linked to the plasticity at the crack tip, the latter will be measured by a Data-Driven approach and characterized by topological descriptors of the plastic zone forming a Plastic Flow Indicator (PFI). The crack will also be described by an extended SIF (SIF++) that includes T- and B- stresses related to structure/constraint effects. The GIM model consists in searching the experimental database to obtain, during an elastic numerical simulation, the crack growth rate estimate from the evaluation of the SIF++ along the crack front and the evolution of the PFI. The proposed methodology can be summarized as follows: (1) A structural material: a fine-grained Al-Si casting alloy with silicon particles; (2) Overload fatigue tests performed under synchrotron tomography to distinguish the fine Si particles and follow the 3D crack growth. Complementary 2D tests allowing to vary the effects of structure/constraint; (3) 2D/3D field measurements allowing to understand the mechanisms acting during an overload by monitoring the crack and the propagation velocities but also the extraction of SIF++; (4) The data will feed the database of the GIM model with the SIF++ and the PFI deduced from the displacement fields by a Data-Driven approach; (5) The validation will consist in reproducing, by a 3D X-FEM numerical simulation using the GIM, the experimental observations. To achieve these goals, the 4 partners will share their expertise in aluminum alloy metallurgy (CTIF), in fatigue tests coupled with field measurements (LaMcube) and performed in situ under X-ray tomography (MATEIS) and in Data-Driven identification techniques (GeM). This collaborative project meets the objectives of the "Metallic and Inorganic Materials and Associated processes" axis. It will enable an understanding of 3D cracking mechanisms by coupling in situ tests with measurements of an unseen resolution in 3D. The richness of the experimental data will allow to propose and validate a new 3D propagation prediction model that can be implemented in any software. More predictive tools will give more reliable structures, for example in transport and energy.