Dac Loi Nguyen

New methodology for identifying local mechanical properties of a heterogeneous material by nanoindentation : application to civil engineering materials

Advisors: Luc Dormieux, Denis Garnier, Camille Chateau

The present work proposes and develops a complete methodology for identifying the local mechanical properties of a heterogeneous material at the scale of the constitutive phases. It is a combination of very diverse skills in theory, in numerical simulation and in experimentation. More precisely, the theoretical part concerns the determination of the nano-micro relations for the indentation module; the numerical part based on the yield design theory is carried out to find the last relations applicable for the hardness; and the last part is performed to obtain homogenized properties by the experimental way using the nano-indentation technique. The experimental study of the thesis is for the purpose of determining indentation properties of different cement paste samples. A complete experimental program, is developed, which allows characterizing the main phases at the micrometric scale of this material, among which we are mainly interested in the C-S-H matrix phases. The modeling of the problem related to the penetration of an indentation point into a material is studied. For this, the first way, based on the kinematic approach of the yield design theory, consists in trying to construct ruin mechanisms analytically, then to make them evolve according to the change of the initial geometry, in order to obtain the corresponding ultimate load. The second way is then to follow the same approach, but by building numerically these ruin mechanisms. The obtained load depends naturally on the retained criteria parameters, which are determined by the combination with the experimental results. The Von-Mises and Tresca strength criteria for purely coherent materials as well as the elliptical one are examined in this work.


Comments are closed