From cracking prediction in structures to applied mathematics lab

Breno RIBEIRO NOGUEIRA

LinkedIn, ThesesFr, Research Gate

Merci pour le témoignage.

Could you please describe your journey towards a PhD?

I enjoyed thinking about and discussing every subject in general, but since I was passionated by maths and physics since I was a kid. Before joining my university in Brazil, I wanted to do philosophy. Then, I changed my mind to do physics, and after all, I finished by getting a good grade in the “Concours” to enter the civil engineering program at my hometown university. Inspired by my father’s career as a civil engineer, professor, and researcher, I was always interested in more theoretical subjects and soon became involved in some “initiation to research” projects. Fortunately, I met people who guided me toward interesting subjects related to applied mathematics in mechanics and numerical analysis. During my last year at the university (2016-2017), I had the opportunity to do a one-year exchange at ESTP Paris and work as a structural engineer intern at Vinci Construction Maritime et Fluvial, starting my journey in France.

In Brazil in 2018, I graduated and started working as a structural design engineer. At the moment, I did not feel delighted and thought that I could spend my time exploring the research world, so I decided to apply for Master’s opportunities in France. In 2019, I returned to France for an M1 and an M2R at ENS Paris-Saclay. Back there, I understood that I loved research and that it was what I wanted to do for a living. I had the opportunity to do two different internships as a collaboration between the old LMT (Laboratoire de Mécanique et Technologie, Cachan) and CEA (Commissariat à l'Énergie Atomique et aux Énergies Alternatives) in subjects related to damage and fracture mechanics. At the end of my M2R, I started to look for PhD opportunities. Fortunately, we could make up a project in collaboration with the new LMPS (Laboratoire de Mécanique Paris-Saclay, ENS), Università degli Studi del Molise, and CEA Saclay.

Please briefly describe your PhD thesis work.

My thesis concentrated on studying cracking nucleation and propagation, which are essential to assess realistic structural performances. For instance, this is the case for analyzing sensible structures, with little room for errors. The crack opening is an essential input data for estimating leakage rate through containment walls of nuclear power plants. In this context, predictions must be more accurate and provide helpful information about remaining service life. Studying material degradation plays a significant role in these estimations.

Therefore, my thesis's main aim was to provide theoretical and numerical developments concerning modeling degradation mechanisms in quasi-brittle media (e.g., concrete). The objective was to provide, in fine, a reliable and robust numerical framework for predicting cracking in structural simulations through the framework of non-local continuum damage mechanics. The project involved several mathematical aspects and numerical tools for developing models, but no experimental tasks were carried out. The obtained results could be compared to the existing experimental data from the literature.

In your opinion, what are the most important things that you could learn from the experience of doing a thesis?

There are plenty. From the work side, these were the most intense three years of my life. I learned a lot through it:  how I can manage my work, develop my independent researcher spirit, deal with different kinds of people, work on presentations and public talks, and exponentially grow my scientific knowledge, among other things.

From the personal side, I could improve my self-confidence a lot, but the reader may have in mind that it could be expected to question yourself a lot of times during the three years. In the end, which is the most important thing for me, we see that life goes on, and we should see the thesis as another everyday standard job.

What are your plans, and which subject are you working on?

Right after my thesis, I got a Post-doc position at the Centre de Mathématiques Appliquées, à l’École Polytechnique. Nowadays, I work on a completely different subject. Still, it could relate entirely to all I learned during my master’s and thesis regarding mathematical and physical tools. The postdoc work concentrates on topology optimization of hyperelastic lattice structures through asymptotic homogenization theory. One of the project's main ideas is to extend existing works to the case of nonlinear material behavior and accelerate computations through the use of neural networks.

In the future, I plan to work in the research field, either in academia or in more applied subjects. Teaching is also another passion that I will not forget…

Which message would you like to give to students who plan to do a PhD?

It will be a very intense period of your life, both at work and personally. It may be hard sometimes, but at the same time, a prosperous time for discovering and learning a lot. If you love research, go ahead and enjoy it.