Abstracts
Chemo-mechanics and damage coupling by means of a phase field approach
For energy storage, computational approaches are transforming battery storage technologies. For understanding multiphysics processes, highly accurate and coupled solution algorithms are needed. Specifically for batteries, ions are moving due to chemical potential and thus also stress assisted flux needs to be modeled. Ion insertion (lithiation) causes swelling leading to microcracks and loss of capacity. Such a coupling between mechanics and diffusion makes numerical difficulties in solving of the set of nonlinear and coupled field equations. Moreover, different materials are possible and their material properties are difficult to obtain from the literature. The biggest challenge is then a validation since the battery producers measures quantities that needs to be correctly interpreted to the solution of field equations. We discuss these challenges and provide some answers. All computations are done by open-source packages with symbolic derivatives providing high accuracy at the coupling terms and material properties may be obtained from existing databases based on computational and experimental results.
From simple architectures to rich phenomenology: the case of pantographic waveguides
Pantographic waveguides represent a distinctive class of mechanical metamaterials whose response is governed by the interplay of geometric constraints and nonlinearity. Their architecture, an array of hinge-connected slender elements arranged in a diamond-shaped lattice, enables large deformations with minimal energy cost, followed by a rapid transition to a stiffened regime as the cells approach full extension.
In this talk, I will demonstrate that elastic rarefaction solitary waves can propagate in monolayered pantographic waveguides. The analysis will be conducted within a homogenized continuum framework derived from a discrete lattice model endowed with Hookean interaction potentials.
Effective Dynamics of Disclination Pairs
We study the dissipative dynamics of a pair of wedge disclinations with opposite Frank angles confined to a circular domain. Under radial symmetry, we identify two distinct regimes: disclination divergence and dipole annihilation. We characterize the corresponding stationary configurations and their stability, and estimate the characteristic time scales near these states. In the annihilating-dipole regime, we further show that, after a suitable rescaling of time, the dynamics converges to the motion law of an edge dislocation.
Chiara Gavioli
Modeling fluid diffusion in partially saturated porous media
This talk explores fluid diffusion in partially saturated porous media, focusing on how surface tension induces hysteresis in the pressure-saturation relation. We model this via a Preisach operator, leading to a challenging, degenerate $N$-dimensional problem. I will present a convexification argument to prove the existence of solutions, showing how this approach remains valid even when accounting for gravity, viscoelasticity, and saturation-dependent permeability.
Ivan Giorgio
Designing Metamaterials Through Curved Rod Lattice Shells
A nonlinear elastic model for nets composed of two families of curved fibers is proposed. Although the net starts out flat, its equilibrium configuration, found by minimizing total potential energy, can deform into a fully three-dimensional surface. The model captures stretching, bending, and torsion in the fibers, treated as a continuous distribution of Kirchhoff rods.The model predictive power and its limits are illustrated using a cycloidal orthogonal fiber pattern as a case study, validated through a numerical micro-macro identification against a standard continuum model at the fiber scale. Finite element simulations, including static and dynamic (modal) analyses, provide further comparison.
Fatigue-fracture characterisation for soft materials: combining numerical simulations with experimental study
Soft matter such as multi-functional rubber-like materials and active hydrogels gain unprecedented attention in recent years thanks to their wide-spread potential applications in soft robotics to drug delivery in healthcare sectors. While applications of soft matter are increasing exponentially, robust synthesis techniques and appropriate experimental set-ups of these complex materials are paramount. Experimental characterisations of soft matter are multi-facets. On the one hand, soft materials have complex mechanical and physical characteristics such as extreme deformations, strain and time-dependence, stress-softening, degradations, temperature and environment sensitivity. One the other hand, sample preparations from materials, representations and fixations within experimental set-ups; data extraction and monitoring etc face challenges due to their finite deformations and intricate micro-mechanical structures. In this talk, several challenges in the case of experimental characterisations of soft polymers will be presented followed by their potential solutions that have been identified in our lab over the last few years.
The Principle of Virtual Work and the Problem of Synthesis of Metamaterials
An old controversy about the most suitable postulation foundation of mechanics revives in the modern problem of the synthesis of metamaterials.
We claim that a large class of Exotic mechanical material properties can be obtained by suitably designing the novel material’s microstructures.
Even if no general synthesis theorem is yet available we give some preliminary results and we underline that the most effective postulation scheme to be used in mechanics has to found it on the principle of virtual work .
Indeed in this framework: i) homogenisation results are more easily obtained ii) generalised continuum models can be consistently formulated, iii) the same conceptual structure is used at micro and macro level and iv) well-posedness results and numerical predictions are more easily obtained.
Pantographic, generalised Hart’s investors and ZAPAB microstructures are presented as examples of obtained synthesised microstructures with numerical and experimental evidence showing their peculiar behaviour.
Variational formulation of planar linearized elasticity with incompatible kinematics
We address mechanical equilibrium in the planar strain regime for systems with incompatible kinematic from a variational standpoint. We show that, for non-simply connected domains, the equilibrium problem for a non-liftable strain-stress pair can be reformulated as a well-posed minimization problem for the Airy potential. We characterize the additional compatibility conditions on the internal boundaries of the domain as Volterra dislocations or disclination.
Finally, we establish that the minimization problem for the Airy potential can be reduced to a finite-dimensional optimization involving cell formulas.
This is work in collaboration with Pierluigi Cesana (Kyushu University) and Edoardo Fabbrini (INRIA, Grenoble).
A Defect-based Approach to Micropolar Fracture Mechanics
A defect-based framework will be presented for fracture mechanics in polar media. Cracks are represented by continuous distributions of dislocations and disclinations, corresponding to displacement and rotational discontinuities, respectively. The formulation is developed within micropolar, nonlocal micropolar, and gradient micropolar elasticity. The resulting crack fields reveal the influence of generalized continuum effects and intrinsic material length scales: while the classical micropolar formulation retains singular crack-tip fields, nonlocal and gradient micropolar theories lead to singularity-free solutions. The work thus systematically extends dislocation-based fracture mechanics to a dislocation–disclination-based framework for polar media.
The Jeffery equation for Newtonian and micropolar background flow
Jeffery's theory describing the rotation of rigid ellipsoidal particles in a Newtonian Stokes flow has remained a cornerstone of suspension mechanics for more than one century. Despite its fundamental importance, the original presentation is written in an archaic notation that obscures many of the underlying physical and mathematical arguments and complicates extensions to generalized continua. In the present paper, the classical Jeffery theory is first reformulated in a modern tensorial framework, providing a transparent derivation of the governing orientation equations and their analytical solution for the case of spheroids. The properties of the analytical solution will then be extensively discussed. Moreover, building upon this formulation, the theory is generalized to a micropolar background fluid by replacing the classical velocity-gradient kinematics with the corresponding micropolar measures. The resulting Jeffery-type equations reveal how the intrinsic spin of the surrounding fluid modifies the particle rotation while preserving the overall mathematical structure of the original problem. Furthermore, the implications for the particle-induced stress contribution and for the effective viscosity response in dilute suspensions are investigated. Finally, the applicability of the generalized Jeffery dynamics is discussed for approximately linear micropolar Couette flows including the form of an appropriate stresslet and its impact on particle-induced stress contributions. The presented framework establishes a consistent bridge between classical suspension mechanics and micropolar continuum theory and provides a basis for modeling suspensions in fluids possessing intrinsic rotational degrees of freedom.
A two-dimensional variational approach to the modelling of ferronematic thin films
Short abstract:
Colloidal suspensions of magnetic particles in liquid crystals are complex fluids that show a coupling between the magnetic particles and the surrounding liquid crystal, which we assume to be in the nematic phase. The material is then referred to as ferronematics. The coupling results in special effective material properties and potential applications in display technologies or multifluidics devices.
I will present a variational approach that combines the Landau-de Gennes approach for nematic liquid crystals with the theory of micromagnetics for thin films.
This is joint work with Shilpa Dutta, James Dalby and Apala Majumdar. I will show our analytical findings as well as our numerical results obtained as stable ferronematic equilibria by solving the related gradient flow equations. We observe the influence of the stray field on interior nematic defects and magnetic vortices.
Modeling of dynamic issues of high-speed railway subgrade
Short abstract:
The operational safety of high-speed trains (operating at speeds approaching 400 km/h and even higher) is highly sensitive to track irregularities. Such irregularities occur far more frequently on subgrade sections than on bridge and tunnel sections. This presentation introduces subgrade dynamic modeling in three parts:
- First, macroscopic models of the vehicle–track–subgrade coupling system in both the time and frequency domains are presented, along with the dynamic responses induced by stiffness irregularities.
- Second, the mesoscopic mechanical evolution of subgrade soil under high-frequency dynamic loads and its corresponding modeling method are illustrated.
- Third, the predictive modeling of subgrade deformation caused by adjacent construction activities is discussed.
Thermally Induced Shape Transformation in 4D-Printed Liquid Crystal Elastomers
Short abstract:
Thermally induced shape transformations in liquid crystal elastomers (LCEs) result from the interplay between mesogen orientation, material properties, and large deformations. This work presents a continuum modeling approach in which the degree of mesogen alignment is described by a temperature-dependent orientation parameter. The parameter is incorporated into a multiplicative decomposition of the deformation gradient, separating elastic, classical thermal, and transformation contributions. Effective stiffness and thermal expansion properties are obtained using Mori–Tanaka homogenization, while the nonlinear mechanical response is described within a finite element framework. The approach is applied to 4D-printed LCE structures undergoing temperature-induced deformation. The simulations reproduce the characteristic large-scale shape transformation and provides a physically grounded alternative for predicting complex LCE shape changes
Mahmoud Mousavi
