Strength properties of nanoporous materials: Theoretical analyses and Molecular Dynamics computations
Since the recent arising of advanced nano-technologies, as well as of innovative engineering design approaches, nanoporous materials have been extensively studied in the last two decades, leading to a considerable worldwide research interest in both industrial and academic domains. Generally characterised by high specific surface area, uniform pore size and rich surface chemistry, nanoporous materials have allowed for the development of challenging ultra-high performance devices with tailorable properties, finding widespread application in several technical fields, including civil and environmental engineering, petroleum and chemical industries, aeronautics and biomechanics. In order to fulfil to these promising applications, one of the most fundamental research aspect consists in characterising and predicting the strength properties of these materials, as dependent on the size of voids. Since the current lack of an exhaustive benchmarking evidence, as well as of a comprehensive theoretical modelling, the central purpose of the present thesis consisted in: Investigating strength properties of in-silico nanoporous samples via Molecular Dynamics computations. In detail, a parametric analysis with respect to the void radius and for different porosity levels has been carried out, by considering different loading paths with a wide range of triaxiality scenarios. As a result, the influence of void-size effects on the computed strength properties has been clearly quantified, also highlighting the dependence of the predicted material strength domain on the three stress invariants; Establishing engineering-oriented theoretical models able to predict macroscopic strength properties of nanoporous materials, by properly accounting for void-size effects. To this end, theoretical approaches based on both non-linear homogenization techniques and kinematic limit-analysis strategies have been proposed. As a result, closed-form macroscopic strength criteria have been derived, allowing for a consistent description of void-size effects and taking into account different local plastic behaviours.
Additional InformationRecipient Prix Paul Germain 2017: biennial prize for best PhD in Mechanics in Feance. This thesis has been written during my position as a joint-supervised doctoral candidate at the University Pierre and Marie Curie, and at the University of Rome "Tor Vergata". I would express my deeply-felt gratitude to my PhD advisors, Giuseppe Vairo and Djim´edo Kondo, for their expertise, invaluable advice and continuous support throughout my studies, as well as to made research in mechanics fascinating to me. I sincerely treasure their precious remarks about academic writing, research and future perspectives, and I am honoured to acknowledge their mentoring along the way. They listened to me whenever I was excited about a new idea, sharing their enthusiasm and investing their time in any stage of this three-years-long period of personal growth. I look forward to continue our collaboration in both research and life. My heartfelt appreciation also extends to Prof. Franco Maceri, who expertly guided me through my higher education by encouraging my passion in learning, and whose truly inspiring example turned me towards teaching and academics. I am extremely grateful for his wisdom in pushing me further than I thought I could go. I would like to express my sincere gratitude to the members of the dissertation committee: Profs. F. Auricchio, V. Tvergaard and J. Yvonnet, who have kindly accepted to review the thesis, as well as Profs. R. Brenner, A. Corigliano, F. Maceri and A. Molinari. I am extremely grateful for their willingness to take part in my doctoral examination, as well as for precious comments and insightful questions they provide on the present research work. PhD is not a lonely task. I was given the valuable opportunity to work in two different countries, and I would express my deep appreciation to Italian and French colleagues, for helpful discussions and priceless teaching experience.
Accepted Version - PhD_Thesis_Brach.pdf