The Belgian National Committee for Theoretical and Applied Mechanics (NCTAM) is pleased to announce that the 2018 edition of the Award distinguished a young scientist from iMMC (UCL) who has recently completed a PhD thesis in the field of Mechanics.
Jérémy Chevalier received the NCTAM award with his PhD thesis entitled "Micromechanics of an epoxy matrix for fiber reinforced composites : experiments and physics-based modelling" (prom. : Pardoen, Thomas ; Lani, Frédéric, 19/11/2018).
The doctoral thesis of Jérémy Chevalier, supervised by Prof. Thomas Pardoen and Dr. Frédéric Lani at the Mechanics, Materials and Civil Engineering Institute (iMMC) at UCLouvain, aimed at understanding, characterizing and modeling the mechanical behavior of an epoxy resin used as a matrix in high performance composite materials reinforced with fibers. These materials have become first-class solutions for reducing the weight of structures, such as aeronautics, for example. However, the complexity of the mechanics of composite materials is still a hindrance to the accuracy of numerical predictions, motivating a bottom-up approach based on a good understanding and modeling of mechanisms at the level of their components.
Summary of the thesis
Given the multi-scale nature of the damage and deformation mechanisms in fiber reinforced composites, bottom-up approaches are believed to be the more efficient strategy to develop generic models for the predictions of the mechanical behaviour of large structures. These analyses start at the microscopic scale, where reliable models for the constituents are essential input ingredients. This thesis is dedicated to the characterization, understanding and modelling of the fracture and deformation mechanisms of the RTM6 epoxy resin.
A first part of the thesis aimed at unravelling the origin of crack initiation in epoxy resins. It provided a physical explanation of the pressure dependence of the fracture stress and strain in highly cross-linked epoxy resins, unifying the occurrence of fracture under a wide range of stress triaxialities based on a single mechanism.
A second part of the thesis was devoted to the microscale characterization of RTM6 in a unidirectional composite, based on in situ experimental tests providing quantitative pictures of the strain field at the microscale. The comparison between experimental results and finite element analyses both at the macro- and microscale enabled a critical assessment of the validity of macroscopic properties at the microscopic scale.
Finally, a novel modelling approach based on the shear transformation zones framework was developed for epoxy resins. The proposed approach offers an alternative to complex phenomenological constitutive models, reducing the number of parameters from more than twenty to seven, while bridging the gap between atomistic and continuum mechanics approaches by providing the missing ingredients for seamless scale transition.