Plenary lecturers

Henryk Petryk

Institute of Fundamental Technological Research,
Polish Academy of Sciences, Warsaw, Poland

Thermodynamic approach to macroscopic modelling of inelastic solids with microstructural instabilities

Henryk Petryk is Professor at the Institute of Fundamental Technological Research (IPPT), Polish Academy of Sciences, Warsaw, Poland. He received the title of Professor in 1995, became the head of the Department of Mechanics of Materials at IPPT in 2007, in 2012-2018 he was the chairman of the Scientific Council of IPPT. Member of the Polish Academy of Sciences, visiting Professor in Germany, France, Japan, Italy, China. His research interests focus on the mechanics of solids, mainly on theory of plasticity, bifurcation and instability, variational methods, micromechanics of materials, evolution of microstructures in metal crystals and shape memory alloys, internal length scales and size effects. He published over a hundred papers, most of which focused on fundamental problems in solid mechanics, 40 as the sole author. He has been the Editor-in-Chief of Archives of Mechanics since 1999. He served as Associate Editor of European Journal of Mechanics A/Solids, 1995-2004, and Comptes Rendus Mecanique (Paris), 2001-2009. From 2016 to 2022 the Secretary-General of IUTAM (International Union of Theoretical and Applied Mechanics).

Microscale instabilities cause a number of paradoxes when applying classical thermodynamics of irreversible processes to macroscopic models of inelastic phenomena. Fast microstructural rearrangements related to plasticity, damage growth, mechanical twinning, diffusionless phase transformations, etc. can be considered as a physical source of rate-independent dissipation on a slow time scale of external loading. The classical Gibbs condition for thermodynamic stability of equilibrium has been modified accordingly. Its key consequence is the general first-order variational principle for inelastic evolution with rate-independent dissipation. This is discussed for dissipative solids with internal variables of the local, gradient or interfacial type, including a phase-field approach that combines viscous and rate-independent dissipation. Straightforward extension of the first-order principle to second-order or finite increments corresponds to the incremental energy minimization approach, but its application is limited to potential problems. A more refined extension, suitable for non-potential problems of rate-independent evolution, is derived from thermodynamic considerations in the form of the quasi-extremal energy principle, in which the minimized function depends on an unknown solution as a parameter. This works in the general case where the usual variational or extremal principles fail. The theory is illustrated by a number of applications in conventional and gradient plasticity of metal single crystals and polycrystals, as well as in multiscale analysis of martensitic phase transformation and twinning in shape memory alloys.

Javier Segurado

Universidad Politécnica de Madrid
& IMDEA Materials Institute, Spain

Stochastic approaches coupled with FFT solvers for simulating defect interaction and evolution in metals.

Professor Javier Segurado graduated in Materials Engineering at the Technical University of Madrid (UPM) in 1999 and got his Ph.D. in the same university in the year 2004. He holds a Full Professor position in Solid Mechanics at the UPM, and since 2008 has a double appointment as researcher at IMDEA Materials Institute. Prof. Segurado is a Fulbright scholar and has held visiting positions at UCLA, Los Alamos National Laboratoy (USA), TU-Wien (Austria) and Mc Master University (Canada). His research activity is focused on the prediction of the effect of the microstructure on the behavior of heterogeneous materials using continuum micromechanics and other simulation techniques at lower length scales including Molecular Dynamics, Discrete Dislocation Dynamics, Crystal Plasticity and multiscale modeling approaches. He has also experience in the development of tools based on the Fast Fourier Transform for solving different problems at the microscale. He has published more than 100 papers in the most important journals in computational solid mechanics or computational materials science and has more than 500 citations and h-index of 42 (scopes). He has participated in more than 40 research projects with international, European and national funding, including FET-open and Clean-sky European calls, leading many of them. He is included in the list of the top 2% scientists in the ranking developed by University of Stanford.

Object Kinetic Monte Carlo (OkMC) approach allows to simulate the time evolution of microscopic systems controlled by stochastic processes without the computational cost of atomistic approaches. The elastic fields distribution within the microstructure plays a fundamental role in the activation energy of the processes considered, and FFT solvers arise as a general and very efficient tool to complement OkMC models with elasticity. Two different case studies are presented. The first one consists in a framework to include the elastic interaction energy effect in the migration of nano-scale radiation induced defects. As examples, the migration of prismatic loops and self-interstitials in iron are studied, accounting for their mutual interaction and with other immobile dislocations. The second case is a model to study the plastic deformation of a metal in submicron regions, sizes at which the averaging nature of crystal plasticity is not fulfilled but which are too large to be described by discrete dislocations. In this case the representative examples are submicron-pillars and nano-porous metals in which discrete plastic events with stochastic nature are considered. 

Paul Steinmann

Erlangen-Nürnberg, Germany

In the treadmill: the weirdness of flow-immersed soft particles

Following his doctorate in engineering in 1992, Paul Steimann received Venia Legendi for Mechanics in 1996, and became full professor at University Kaiserslautern in 1997. In 2007, he became full professor at FAU Erlangen-Nürnberg, where he is active since. He declined offers for a full professorship at RWTH Aachen and the prestigious Regius Chair at University of Glasgow, UK, in 2012 and 2017, respectively. Since 2017 he is Co-Director of the Glasgow Computational Engineering Centre (GCEC) at the University of Glasgow, UK.

His research interests are in the fields of material modelling, multi-scale methods, multi-physics problems, non-standard continua, configurational-failure-fracture mechanics, biomechanics, optimisation as well as general developments in finite element and discretisation methods.

Co-authors: Jana Wedel, Matjaz Hribersek, Jure Ravnik

Flows of particles suspended in fluids remain a challenge in various branches of science and engineering. This is especially true for particles in the micron-size range, since there the complexity and cost of experimental techniques and corresponding computational models of particle-fluid interactions is highly demanding.

In this presentation, we will focus on novel computational models for tracking the motion and deformation of large numbers of micron-sized soft, i.e. highly deformable, non-spherical particles in fluid flows. We will discuss particles with a variety of rheological properties allowing a prominent change in the particle’s geometry. Thereby, we will dedicate special attention to the pertinent force and torque models for particle-fluid translational and angular momentum exchange. As a result, we will especially focus on the tank-treading phenomenon displayed by flow-immersed soft particles.

Christophe Martin

Grenoble-INP, France

Discrete Element Simulation for particulate materials: from compaction, to sintering and fracture

Christophe Martin is a CNRS research professor in the SIMaP laboratory at the Université Grenoble Alpes (UGA) in France. His research focuses on particulate media, with a particular interest for powders with engineering applications. He is the principal investigator in the development of a discrete element code, dp3D. Applications mainly concerns materials for energy applications. He has recently been appointed dean of the I-MEP2 engineering doctoral school at UGA.

This talk reviews recent advances in simulations based on the Discrete Element Method (DEM) applied to particulate materials. Typically, starting from a ceramic powder, the material is pressed and then sintered. During compaction, defects may arise due to density heterogeneities, spring-back effects upon unloading or ejection. Similarly, sintering may also lead to defects such as cracks when constraints arise. Once the part has been sintered, its mechanical behavior, and in particular its fracture behavior is obviously of interest. DEM is naturally well suited to modeling compaction and sintering, as particles are explicitly modeled. DEM is also a powerful method to simulate the fracture behavior of dense or porous ceramics, as it naturally allows us to track the topological modifications (branching, bifurcation) that accompany fracture.

The Discrete Element Method is first presented to give a general overview. We illustrate DEM’s capabilities on ceramics with several examples using our in-house code dp3D, which is dedicated to materials science. These examples are meant to give a general idea of DEM applications. For example, we show how such simulations can be effectively coupled to X-ray tomography images that can be used as input data for realistic initial microstructures. Crushing of porous ceramics that include notches, the fracture of partially sintered ceramics and of nacre-like alumina offer examples of application of dp3D. High temperature sintering also provides a good example of the potential of a discontinuous approach to tackle grain growth. Finally, the possibilities of deviating from spherical particles offered by the Level Set method are illustrated for both compaction and sintering.

Zhuo Zhuang

Tsinghua University, Bejing, China

Theoretical and computational model of shell fracture and engineering application

Zhuo ZHUANG, Professor, School of Aerospace Engineering, Tsinghua University. Vice President of International Association for Computational Mechanics (IACM). Ph.D., University College Dublin, Ireland, 1995. Honorary Doctor Degree (EngD), Swansea University, UK, 2017. Chief scientist of national fundamental research projects of China. Published 360 journal papers and 2 books in English by Elsevier and 10 books in Chinese with 14,000 citations.

A novel unified theory of continuum-based shell fracture mechanics is proposed, which integrates computational model of thin and medium-thick shells. Through orthogonal decomposition of stress and displacement fields, the criterion of crack propagation and arrest based on the maximum energy release rate is formed. The calculation method of natural selection propagating path of shell cracks under large deformation frame is established, and the interaction of multiple cracks under dynamic and static loads is revealed. This work results in designing new light weight structures, for example, the core cabin of Chinese Space Station “Tianhe”. By reducing stress concentration and optimizing reinforcement layout, the weight reduction is nearly 10%. It is proved that ground tests simulating temperature variation is ±100 degrees for the cabin facing and facing away from the sun, in-orbit fatigue life is larger than 22.5 years.

Danny Van Hemelrijck

Vrije Universiteit Brussel, Belgium

Additive manufacturing, an emerging technology with a bright future?

Danny Van Hemelrijck (ORCID 0000-0002-5228-9307) is Full Professor at the Department of Mechanics of Materials and Constructions (MeMC) of the ‘Vrije Universiteit Brussel’ since October 1996. He received his PhD degree from the same department and university in 1992. His research has a clear focus on the development, the mechanical characterization and on the design and analysis of innovative lightweight material systems and constructions. The mechanical performance of these material systems and constructions are studied under complex loading conditions by means of (combined) experimental testing and advanced numerical modelling.

Co-authors: Kalliopi-Artemi Kalteremidou, Yifan Zhu , Amalia Katalagarianakis, Ahmad Shawki Charkieh, Lincy Pyl

Unlike traditional manufacturing processes, which involve the subtraction of material by milling, drilling, grinding, etc., additive manufacturing (AM), or 3D-printing, is based on the addition of material to create an object. Starting from a CAD-file a 3D-object is created by successively adding material layer by layer until the entire part is complete. AM having the ability for reducing costs and waste, increasing quality, and shortening production times, is driving a change in many industries such as aerospace, healthcare, automotive and consumer goods, among others and not only for ‘rapid prototyping’. Indeed, at present there is a real interest from different industries to introduce AM-produced parts into final designs. However, there are several remaining challenges before this technology will become the main way to manufacture functional objects as for instance, the limited availability of materials, the influence of residual stresses, the anisotropic behaviour or how local heterogeneities affect the global mechanical properties. Therefore, the majority of recent AM research focuses on the improvement of the mechanical properties and object quality using various experimental techniques and concepts. It will be illustrated that the use of different experimental methods is of major importance for AM to keep up its promise that it will revolutionise the way products will be designed, manufactured, and supplied. This exercise will be executed both for AM of metals as well as for continuous reinforce polymer matrix composites.