Keynote Lectures

Javier Dominguez

National Center for Nuclear Research
Otwock-Świerk, Poland

Session TS1

Advanced continuum theories

Unveiling Plastic Deformation Mechanisms of BCC W- based and FCC Ni-based Solid Solution Alloys through Machine-Learned Atomistic Simulations

Dr. hab. F. Javier Dominguez achieved his PhD in Computational and Applied Physics with Summa Cum Laude honors at the National University of Mexico (UNAM). During his doctoral and postdoctoral studies, he joined The Institute for Advanced Computational Science at Stony Brook University, where he focused on modeling plasma-material interactions in tokamak plasmas, collaborating with the Princeton Plasma Physics Laboratory in the USA. Before joining the National Centre for Nuclear Research (NCBJ) in Poland, he was the recipient of the A. von Humboldt Research Fellowship and a Siemens Foundation scholarship at the Max Planck Institute for Plasma Physics in Germany. During this period, he created the innovative FAVAD software workflow using machine learning methods to characterize and visualize defects in damaged materials. Notably, FAVAD won the IAEA challenge, showcasing its excellence. In 2023, he attained the title of doctor habilitus (D.Sc.) in physics and an associate professor position at NCBJ. He's been invited to speak at institutions like Aalto University, Karlsruhe Institute of Technology, University of Helsinki, VTT, IPPT, and AGH University. Within NCBJ, his primary research focus on developing multi-scale numerical models seeking to understand how single crystal materials and high-entropy metal alloys respond under extreme conditions, such as high temperatures and irradiation doses. The overarching goal is to engineer and design materials suitable for applications in fusion, fission, and various industrial sectors. Dr. Dominguez actively participates in platforms like the EERA JPNM, EuroFusion, INNUMAT project, Humboldt Foundation, and EuMINe COST ACTIONS.

Deciphering the plasticity mechanisms in novel alloys is crucial for optimizing their mechanical properties. This study employs a comprehensive series of machine-learned molecular dynamics (ML-MD) simulations to investigate the nanomechanical response of single crystals in BCC W-based and FCC Ni- based solid solution alloys by nanoindentation test. We analyze dynamic deformation processes, defect nucleation, and evolution, alongside concurrent stress–strain responses. Additionally, atomic shear strain mapping provides insights into surface morphology and plastic deformation. In BCC metals, the introduction of Mo, Ta, and V atoms into the W matrices induces lattice strain and distortion, enhancing material resistance to deformation. This impedes dislocation mobility, especially for dislocation loops with a Burgers vector of 1/2⟨111⟩. Furthermore, we explore the influence of Ta, V, and Mo concentrations in W alloys, focusing on twinning and anti-twinning mechanisms during nanoindentation, contributing to material hardening.

For FCC Ni-based alloys, we observe significant hardening effects due to the presence of Fe, Cr, and Co in the samples. For this case, experimental load–displacement data show qualitative agreement with MD simulation results, providing strong evidence that the main strengthening factors are associated with sluggish dislocation diffusion, reduced defect sizes, and the nucleation of tetrahedral stacking faults. In this context, interstitial-type prismatic dislocation loops, mainly formed by Shockley dislocations, are nucleated during the loading process. Their interaction leads to the formation of diamond-shaped stacking faults, primarily created by ⅓⟨100⟩ Hirth dislocation lines. The observation of both types of defects coexisting in the same plastic deformation zone is consistent with both approaches. Reported mechanical data, measured experimentally and interpreted numerically, also align with microstructural SEM and TEM investigations. Throughout this discussion, the highlights of the advantages and limitations of both conventional interatomic potentials and machine-learned models when simulating nanoindentation tests will be presented and discussed.

Marte Gutierrez

Colorado School of Mines
Golden, Colorado

Session TS8

Geomechanics and granular materials

Viscoelastic Damage Model for the Rate-Dependent, Strain-Softening, and Anisotropic Behavior of Shale

Dr. Marte Gutierrez is the James R. Paden Distinguished Professor at the Department of Civil and Environmental Engineering at Colorado School of Mines (CSM). He has published over 370 papers in book chapters, journals, and conference proceedings, given keynote and invited lectures at several conferences, and has been responsible for more than US$ 25 million in research funding. Dr. Gutierrez is an Associate Editor of three international journals and a member of the Editorial Board of four other international journals. He is the recipient of a Fulbright Scholarship, the 2011 Geotechnical Research Medal from the UK’s Institute of Civil Engineers, the 2017 Applied Rock Mechanics Research Award and the 2020 Rock Mechanics Research Award both from the American Rock Mechanics Association, the 2016 Peter A. Cundall Honorable Mention Award, the Kwanghua Visiting Professorship from Tongji University, and four Best Paper Awards. Dr. Gutierrez’s main research interests are in Geomechanics for Energy, Environmental, and Transportation Sustainability.

A simple constitutive model for loading-rate-dependent shale undrained shear behavior is proposed. The model is based on an extensive characterization of the undrained triaxial compression behavior of shale loaded at different axial strain rates up to the strain softening regime. The model is based on a combination of viscoelasticity and damage mechanics and is formulated to predict the brittle behavior of shales from the pre-peak elastic stage to failure and the post-peak strain softening regimes. Nonlinear stress-strain behavior, shear failure, and strain softening are attributed to damage due to the growth of fractures in the shale. Damage is described by a scalar variable damage D and is assumed to commence when the stress-strain behavior deviates from linear elasticity. Given the randomness in the sample heterogeneities that lead to fracture formation and propagation, the damage is modeled statistically using Weibull’s probability distribution as a function of the strain level. An elastic modulus from a superposition of static rate-independent Young’s superposition and a rate-dependent viscous Young’s modulus completes the viscoelastic damage model. The undrained viscoelastic damage model is extended to full triaxial compression loading condition by adding equations for volume change from compression and dilatancy. The model is further extended to account for anisotropic shear response by using a tensorial instead of a scalar damage parameter. The tensorial damage parameter, applied in the deviatoric stress space, preserved the simplicity of the model. The model adequately represents the complete stress-strain response of shale, including strain softening at different axial strain rates, and accurately predicts the strain rate- and confining-pressure-dependent and anisotropic shear strength of shale. Finally, the model is shown to be thermodynamically consistent in terms of the use of the strain equivalence principle and in terms of energy dissipation following the Clausius-Duhem inequality.

Nicolas Jacques

ENSTA Bretagne
Brest, France

Session TS10

Micromechanics of heterogenous and multi-component materials

On the influence of microscale inertia on the dynamic response of nonlinear porous and cellular solids

Nicolas Jacques is associate professor at ENSTA Bretagne (Brest, France) and member of the Dupuy de Lôme Research Institute (IRDL). His research topics are related to the modelling of high strain-rate phenomena, including damage and fracture, plastic flow instabilities and shock wave propagation, and of fluid structure interactions.

The understanding and modelling of the behaviour of heterogeneous materials, such as porous and cellular solids, under dynamic loading conditions is an important issue for several applications, like the safety of pressurized structures, and the resistance of protective structures to ballistic impacts and explosions. Under dynamic loadings, the materials may experience very high strain rate. This may lead to very large accelerations at the scale of the microstructure and small-scale inertia effect. The aim is the presentation is to analyse and illustrate the influence of microscale inertia on the dynamic response of voided solids. Two problems will be considered. In both cases, dynamic homogenisation techniques have been employed to link the macroscopic response of the materials to their microstructural features.

The first problem is the failure of ductile materials by micro-voiding. A micromechanical ductile damage model has been developed. This model can be seen as an extension of Gurson-type approaches to dynamic loading conditions. The obtained results show that microinertia influences the development of damage. Moreover, microinertia leads to a regularizing effect that limits the mesh sensitivity of the simulations.

The second problem is the response of foams (highly porous solids) under shock compression. An important role of microinertia was also found. In particular, Microinertia affects the shock response of the material (Hugoniot relation) and the structure of shock waves.

Mahmood Jabareen

Technion - Israel Institute of Technology,
Haifa, Israel

Session TS11

Multiphysics and coupled problems

Modeling of electroactive polymers: A multiphysics and multiscale approach

Technion – Israel of Technology, Israel

Electroactive polymers (EAPs) are referred as ”Smart materials”, which are able to convert electrical energy to mechanical work. EAPs are applicable in number of fields, such as robotics, optics, acoustics and biomimetics. The mode of action in EAPs actuators is principally based on Coulomb forces generated by an electric field, which causes the polymer membrane to contract in the thickness direction and consequently lead to lateral expansion. However, a high driving electric field is required for actuating the isotropic electric EAPs that may cause electro-mechanical instability and/or electric breakdown. Promising experimental works suggest that this limitation may be overcome by making electroactive polymer composites (EAPCs), which are flexible and have a high dielectric modulus.

With regards to the computational modeling of EAPs, a numerical scheme has been developed using a reduced mixed finite-element formulation for simulating the nonlinear response of isotropic EAPs. On the other hand, computational homogenization is needed for the simulation of EAPCs. The aim of the present work is to provide an understanding of the mechanisms governing the electromechanical response of EAP and EAPCs undergoing large deformations. To this end, a multiphysics computational framework including the electro-mechanical coupling and the viscoelastic properties of the constituents will be presented. In the context of computational homogenization, the reduced mixed finite element formulation, which eliminates the volumetric locking pathology and circumvents the static condensation as it relies solely on the modified deformation gradient, is adopted to both he macro-scale and microscale. This formulation is denoted by MFE.

Matteo Bruggi

Politecnico di Milano,

Session TS15

Structural optimization and optimum material design

On structural optimization for metal 3d printing

Politecnico di Milano, Italy

Wire-and-Arc Additive Manufacturing (WAAM) is a metal 3D printing technique that allows fabricating elements ranging from simple to extremely complex shapes. Among the others, layer-by-layer manufacturing can be used to produce plates of printed material which are found to exhibit significant elastic anisotropy, whereas dot-by-dot printing is employed to build lattices made of bars whose mechanical properties are affected by the fabrication direction.

Within this context, the design of WAAM components is addressed by formulating problems of structural optimizations that take into account peculiar features of the printing process. Topology optimization by distribution of anisotropic material is exploited to perform the simultaneous design of the shape and the printing orientation of stiff beams and I-beams conceived for production by layer-by-layer manufacturing. Shape optimization based on the force density method is implemented to design funicular geometries for fabrication of reticulated shells via dot-by-dot printing, accounting for manufacturing and failure constraints.

In both cases, the arising multi-constrained formulation of optimal design may be efficiently tackled through methods of mathematical programming. Applications are shown, pointing out the peculiar features of the achieved optimal layouts and of the proposed numerical methods.