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M/F Multiscale modeling of the thermomechanical behavior of a 3D carbon/carbon composite

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General information

Reference : UMR5801-GERVIG2-014
Workplace : PESSAC
Date of publication : Tuesday, May 19, 2020
Scientific Responsible name : Dr. Guillaume GOUEGNAT ; PR Eric MARTIN
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Carbon/carbon composites (C/C) belong to the family of carbon-reinforced thermo-structural composites. Thanks to their excellent thermomechanical properties, even at high temperatures, and their low density, they are widely used in the aeronautic and aerospace fields. 3D C/C composites are made of a tri-orthogonal assembly of carbon rods reinforced by an ex-pitch matrix. This architecture gives the 3D C/C material a peculiar thermomechanical behavior, i.e. linear elastic in the reinforcement axes, and strongly non-linear in off-axis directions. They also exhibit significant variations in their mechanical properties with temperature depending on the loading direction. Previous work has shown that interfaces between rods, and between rod and matrix, play a major role in the non-linear behavior of 3D C/C. A 3D multi-scale modeling approach, including ad hoc interface elements calibrated from indentation tests, has allowed to reproduce the main characteristics of the off-axis behavior of 3D C/C, as well as the qualitative evolution of its properties in temperature. More recently, additional tests carried out on a variant of a 3D C/C material have shown a different interface behavior that eventually leads to an alteration of the macroscopic response of this material.

The objective of this work is to pursue the work already initiated by (i) providing a better understanding of the physical mechanisms governing the specific behavior of the interfaces, (ii) proposing an interface model to better consider damage/friction couplings, and (iii) integrating these interface models, as well as the intrinsic damage of the rods and matrix in finite element simulations. The final goal of this work would be to produce a 3D multi-scale model of the 3D C/C composite allowing to predict its thermomechanical behavior over a wide temperature range and for complex loadings.

The anticipated approach will combine both experimental and numerical aspects with i) morphological and micro-mechanical characterizations of the material and its interfaces –possibly coupled with in situ observations (optical or electronic microscopy, X-ray micro-tomography), ii) the development of interfacial and damage behavior laws, and iii) the realization of numerical simulations to be compared with experimental data.

Work Context

PhD funding by CEA.

LCTS, located on the Bordeaux Campus, is ajoint unit of 4 partners : CNRS, Bordeaux UNiversity , CEA and the Safran group. It has 30+ years of experience in basic research on refractory composites, high-performance materials used in aviation, space and energy applications. LCTS is a single team working in "project" mode in strong relationship with its non-academic stakeholders. It currently contains 33 permanent staff members, some 20 phD candidate and ~4 post-doc researchers.

Constraints and risks

Work in restricted access area, subject to previous authorization by security and defence officer.
Some short visits to CEA center in Le Ripault (38) are to be scheduled.

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