PhD DEFENSE BY FRANCOIS VILLETTE

This PhD was co-supervised by Jean-Francis Bloch and Frédéric Dufour (laboratory 3SR).

The defense will take place in the amphitheatre of the Maison Jean Kuntzmann at 10:30 am. On account of the COVID-19 epidemic, a limited number of participant is permitted.

The attendants are asked to register on the following link

Abstract

The understanding, modelling and prediction of failure in heterogeneous materials are important issues for many applications such as the study of the resistance of civil engineering structures or rock detachments for example. Currently, damage models involve an internal length that is not yet explicitly related to the characteristic lengths of the material. The objective of this work is to study the influence of material heterogeneities on cracking processes using paper as a model material.

Indeed, this material has the property to reveal its structure (fibers and fiber aggregates) by optical transmission and thus allows to monitor the evolution of damage during the rupture. In a first step, the local structural and mechanical properties of the fiber aggregates were obtained from images acquired by X-ray tomography and tensile tests. Filmed tensile tests were then used to visualise the development of the fracture process zone and to relate its dimensions to the post-peak behaviour of the tensile curve.

On the basis of this analysis, a new method of calibration of the internal length was proposed on a non-local continuous damage model. The role of the different characteristic lengths of the material was highlighted by these results which were complemented by the study of the crack propagation statistics in an heterogeneous material using a Fiber Bundle Model that we have extended to spatially correlated random fields of rupture.