Organisation/Company: CNRS
Department: Laboratoire de Mécanique et Génie Civil
Research Field: Engineering » Materials engineering, Physics » Acoustics
Researcher Profile: First Stage Researcher (R1)
Country: France
Application Deadline: 27 Nov 2024 - 23:59 (UTC)
Type of Contract: Temporary
Job Status: Full-time
Hours Per Week: 35
Offer Starting Date: 1 Dec 2024
Is the job funded through the EU Research Framework Programme? Not funded by a EU programme
Is the Job related to staff position within a Research Infrastructure? No
Offer Description This thesis, funded through an ANR grant, will be conducted in collaboration between the research teams PMMD (Physics and Mechanics of Discrete Media) at LMGC (Laboratoire de Mécanique et Génie Civil) and PhyProDiv at the IATE (Ingénierie des Agropolymères et Technologies Emergentes) laboratory of INRAE in Montpellier, France. Collaboration with the 3SR (Sols, Solides, Structures, Risques) laboratory in Grenoble will also provide both numerical and experimental support for this work. Candidates should possess a strong background in physics or mechanics, with experience and interest in numerical modeling and simulation highly desirable.
Plants serve as a renewable resource used across various sectors such as food, pharmaceuticals, chemistry, construction, and biorefinery. However, the residues left behind from these processes, while abundant in carbonaceous matter, are often relegated to low-value applications. To design innovative products, a thorough understanding of the grinding and separation processes of plant residues is imperative, spanning from the process scale down to the cellular level. Predicting size distributions and energy consumption during comminution operations poses a significant scientific challenge, intricately linked to the compositions and histological structures of plant tissues, as well as the complex physics of grinding, including the flow behavior of breakable particles.
The objective of this PhD project is to develop a multiscale approach encompassing at least three levels: 1) plant cell and tissue, 2) residue particle, and 3) plant residue powder (process scale). Classical fracture mechanics, while effective for homogeneous materials, does not adequately address the complexities of heterogeneous media like plant tissues. The statistical distribution and gradients of mechanical properties play a critical role, with micro-cracks forming in weaker phases (voids, cell walls, interfaces) and coalescing into macro-cracks. At the tissue level, parameters such as cell shapes and adhesion between cell walls control crack propagation within and/or across cells, influencing the fracture energy and toughness of residue particles. These particles undergo progressive fragmentation due to mechanical stresses exerted by neighboring particles during milling, resulting in a highly disordered granular microstructure.
The project will start with mechanical and physicochemical interactions at the constituent level for a selection of three different plant types, modeling intercellular dissociation to develop single-particle fracture laws. These laws will be experimentally validated and incorporated into dynamic simulations of a large number of particles at the process scale. The histology of selected plant residues will be analyzed using various imaging systems adapted for plant samples, and nano-indentation experiments will provide sub-micron mechanical properties of tissue components. Simple traction tests on plant tissue samples will be conducted to analyze crack propagation and deformations, informing parametrization of Peridynamics simulations. A bond-based Peridynamics code will be used to simulate plant tissues, integrating experimental data on cellular structures and mechanical properties.
For validation, traction simulations of notched and un-notched samples will be compared with experimental crack propagation data. A particle fragmentation model, accounting for cellular structure and mechanical properties, will be developed for comminution simulations using the Discrete Element Method (DEM). This model will feature particles with an internal texture generated through a constrained tessellation method, with mechanical properties carried by inter-element and intra-element bonds. Calibration of the structure and bond properties will involve single-particle crush simulations and comparisons with experimental data.
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