Material model parameters identification based on full-field measurements
Framework: State-of-the-art models provide a better description of physical processes by introducing multiple scales in space and/or in time which require intensive computer simulations. No matter how refined a model is, however, its academic or industrial usefulness depends on the availability of an efficient procedure for the identification of its parameters. For a long time, whenever multiple parameters of a material model had to be identified, the only option was to carry out a set of basic ``uniform" experiments, each designed to identify a single parameter. A radically different approach consists in accepting the fact that experiments with uniform fields indeed constitute an exception. Real-life and industrial experiments are nonuniform: complex fields of strains, stresses and internal variables can develop. For example, the design and qualification of aeronautical structures rely on basic experiments which, for the most part, consist of tensile tests on perforated plates or low-energy impact tests, which intrinsically induce nonuniform damage states as well as nonuniform elastic and inelastic fields. Although such nonuniform experiments theoretically provide very rich information, there have been only few attempts to tap the potential of these experiments and observations. The main reason for not using rich data (e.g. displacement fields, thermal fields, etc.) is that in the case of nonuniform fields with highly nonlinear models it would be too complex to develop the post-processing procedure manually. A first breakthrough happened in the specific post-processing of observed displacement fields. The use of modern devices such as CCD cameras along with image correlation techniques provided full-field measurements of the displacements which, then, thanks to direct or inverse techniques, were used to identify simple material properties. Since then, these techniques have developed very rapidly. We will here focus on the development of a family of inverse methods, for both 2D and 3D inverse identification. The candidate will have the opportunity to develop his skills, both from the experimental and theoritical point of view. He will be involved in both international conferences and publication in peer-reviewed journals. You are more than welcome to contact us for any detail!
		Displacement field induced by a transverse crack within a laminated composite - 2D measurement

Virtual testing and coupled aging simulations for damage in composites
Framework: An outstanding revolution is the rapid development of simulation both in material and structural design. Unfortunately, we can say that robust models are today limited to static and/or pure mechanical loading. Meeting the modern composites needs requires addressing challenges associated with the use of these materials when subjected to very aggressive (chemical/physical/mechanical) loadings. When exposed to some of these conditions, materials can exhibit fast degradations, which can largely endanger the structural or the functional integrity. A better understanding of the combined loads on the composite structure will contribute to optimize their design. Reliable prediction of physical, chemical and mechanical aging is thus a hot issue, which drives the word-class top research programs. The main reason is that the targeted duration cannot be reached experimentally. Thus, synthesis of experiment and computational simulation is no more an option. However, one should mention that the target of this ``virtual testing" is rarely the direct design of the structure. ``Virtual testing" rather aims to define the experimental set up and the interpretations of accelerated experiments. Increasing the stresses, the temperature or modifying the chemical environment to speed up the degradation can strongly modify the underlying damage mechanisms and the overall phenomenology. Here, simulation is thus a way to ensure that these experiments are still representative of the targeted application. Meeting this challenge requires improvement on two points: numerical multi scale strategies, and modeling: • Multi scale strategies and high performance computing: As far as pure mechanical simulations are concerned, state-or-the-art multi scale strategies are well developed and provide satisfactory results, both for scalability and robustness. Now, a challenging numerical issue in the case of multi physics aging, is that multiple and very heterogeneous time/space scales are involved: mechanical time scale, fatigue time scale, reactive time and so on. Thus, a real breakthrough has to be achieved for solving long-range multi physics problems. • Modeling strategies and physics based models: One of the main challenges is the understanding on the underlying physics and chemistry. Indeed, even if complete coupled mechanical / diffusion / reaction computations can be achieved, we need to be able to formalize the impact of chemical modification on the material properties, or any kind of coupled effect (chemical - material content - mechanical engineering properties - electrical properties). That will only be possible by very-low scale simulations based on molecular models, that require strong collaborations between chemical engineering researchers and mechanical engineers. You are more than welcome to contact us for any details!
		Damage field induced by a tensile test on an industrial laminated composite with hole