Description of the thesis topic

Brittle creep of heterogeneous materials : Time-dependent deformation, damage and rupture of brittle or quasi-brittle materials (rocks, concrete,..) under constant applied stress, is of tremendous importance in various fields, from civil engineering to geophysics. This creep behavior is characterized by several empirical rheological “laws”, some of them known for more than a century, which however still wait for a sound theoretical interpretation. As an example, the Andrade's law [Andrade, 1910] describes the transient, decelerating stage I of creep characterized by a power law decay of the strain-rate. Another example is the Monkman-Grant empirical relation [Monkman and Grant, 1956] between the failure time and the minimum strain-rate, while there are also several evidences for a specific acceleration of the deformation as approaching the failure time (creep stage III). This phenomenology is shared by most of brittle materials, and even beyond by ductile metals, soft matter, and granular media.
The physical interpretation of these empirical laws, as well as the origin of this “universality”, remain largely misunderstood nowadays. In the meantime, the last few years have seen the emergence of new approaches in the study of these rupture processes, based on statistical physics tools and by studying the interactions between microstructural disorder, damage and microfracturing and, in the case of creep, thermally activated processes.

Work Context

The National Centre for Scientific Research (CNRS) is one of the world's leading research institutions. To meet the major challenges of today and tomorrow, its scientists explore living organisms, matter, the universe and the functioning of human societies. Internationally recognised for the excellence of its scientific work, the CNRS is a benchmark both in the world of research and development and for the general public. The National Centre for Scientific Research (CNRS) is a multidisciplinary public research organisation under the supervision of the Ministry of Higher Education, Research and Innovation. ISTerre is a Joint Research Unit of the University of Grenoble Alpes, CNRS, USMB, IRD and Gustave Eiffel University, located at 1381 rue de la Piscine 38400 Saint-Martin d'Hères and on the Bourget du Lac Science Campus. It is part of the Grenoble Observatory of Universe Sciences (OSUG) and the PAGE Research Cluster of Grenoble Alpes University (UGA). It has a staff of around 300 and an average annual budget of €7 million. It is organised around nine research and service teams, with the scientific objective of studying the physical and chemical properties of planet Earth, focusing in particular on the links between observations of natural objects, experimentation and modelling of the complex processes involved.
ISTerre also carries out solid Earth observation missions, hosts and maintains national parks of geophysical instruments, and operates a data centre. The thesis will be carried out within the Fault Mechanics and Instabilities team, as part of the ANR DISCREEP collaborative project, which aims to revisit this creep problem from different angles (experimental, theoretical, numerical), loading configurations and materials. An experimental part will be carried out as part of the ESRF's CHRONOS programme. In this context, the PhD student will be required to interact with other experimenters and theorists. The thesis work will be supervised by Jérôme WEISS and David AMITRANO. The affiliated doctoral school will be the STEP (Earth, Environment and Planet Sciences) Doctoral School at the University of Grenoble-Alpes.

Constraints and risks

This thesis work does not involve any identified risks.