3 PhD positions funded through the Horizon Europe Marie Skłodowska-Curie Actions (MSCA) Doctoral Networks as part of the “Bridging Models at Different Scales To Design New Generation Fuel Cells for Electrified Mobility (BLESSED)” project.

1. Evaluating the Properties of PEMFC Membrane Materials via Molecular Dynamics Simulations | EURAXESS (europa.eu)
2. Transport and Carbon Corrosion in Proton Exchange Membrane Fuel Cells | EURAXESS (europa.eu)

3. Portail Emploi CNRS - Job offer - Physics-based modelling of the PEMFC electrode fabrication process (BLESSED-DC10) M/W

Dear friends, I want to share our recent work on the shape characteristics of 2D crystal blisters. Micro- and nano-sized blisters can form spontaneously when two-dimensional (2D) crystals are transferred onto substrates because liquid molecules that are initially adsorbed on 2D material and substrate surfaces can be squeezed and trapped by interfacial forces. On the one hand, blisters are undesirable in 2D material devices as they impede charge/photon/phonon transport across the interface, so various means were developed to eliminate interfacial blisters. On the other hand, mechanics analysis has elucidated that the blister morphology is a good indicator of the interfacial properties of 2D crystals, such as adhesion. Furthermore, the inhomogeneous strain distributions and the rich surface topographies of 2D crystal blisters can be leveraged for optimizing luminescence and exciton transport in 2D crystals, as well as designing mechanical sensors, microlenses, and more. In this work, we use a combination of experiments, continuum theories, and coarse-grained molecular dynamics (CGMD) simulations to investigate the shape characteristics of spontaneously formed blisters under 2D crystals with heights ranging from a few ångströms to tens of nanometers. We show three distinct regimes in which the height-to-radius ratios (i.e., aspect ratios) of 2D crystal blisters are size-independent, rough linearly proportional, and inversely proportional to the blister radius. We reveal that the blister shape characteristics are governed by three factors: the 2D crystal elasticity, the interfacial interactions, and the phases of confined substances. The characteristic length scales (to which comparing the blister height or radius can define the boundary between these different regimes) are also discussed. We also provide the criteria of the plate-to-membrane theory transition, the Griffith-to-vdW interface transition, and the liquid-to-monolayer-lattice transition regarding the phase of interface substances as practical guidelines for choosing the correct models for 2D crystal blisters.

The publisher link is here; A copy of the manuscript is also available from ResearchGate.

Thanks for your attention.

Sincerely,

Yifan

Two fully-funded postdoctoral positions in computational mechanics of materials and structures are available in the groups of Milan Jirásek (https://mech.fsv.cvut.cz/~milan) and Jan Zeman (https://openmechanics.fsv.cvut.cz/people/jan-zeman). Full description of the openings is available at https://euraxess.ec.europa.eu/jobs/573988, the call closes on 5 December 2020.

Wrinkles are commonly observed in uniaxially stretched rectangular sheets with clamped-clamped boundaries, and can disappear upon excess stretching. Here we explore this wrinkling and restabilization behavior both analytically and numerically. We find that Poisson’s ratio plays a crucial role in the wrinkling and restabilization behavior. Smaller Poisson’s ratio makes later onset of wrinkling, lower amplitude and earlier disappearance of wrinkles. In particular, when Poisson’s ratio is below a threshold, no wrinkles occur, which can be explained by the decreasing transverse compressive stresses with respect to the reducing Poisson’s ratio. Furthermore, based on the Koiter stability theory, we have semi-analytically predicted isola-center bifurcation points, through looking into the sign change of the quadratic terms of potential energy. Both theoretical buckling and restabilization points are in agreement with finite element results. Lastly, a 3D phase diagram on stability boundaries is provided and we find that when the aspect ratio is beyond a threshold, wrinkles may not occur in the center but are split into two packets near the stretching ends.

T. Wang, C. Fu, F. Xu, Y. Huo, M. Potier-Ferry

Int. J. Eng. Sci., https://doi.org/10.1016/j.ijengsci.2018.12.002

Wrinkles commonly occur in uniaxially stretched rectangular hyperelastic membranes with clamped-clamped boundaries, and can vanish upon excess stretching. Here we develop a modeling and resolution framework to solve this complex instability problem with highly geometric and material nonlinearities. We extend the nonlinear Foppl-von Karman thin plate model to finite membrane strain regime for various compressible and incompressible hyperelastic materials. Under plane stress condition, 2D hyperelastic constitutive models can be systematically deduced based on general 3D strain energy potentials, e.g., Saint-Venant Kirchhoff, neo-Hookean, Mooney-Rivlin, Gent model and Gent-Gent model. Moreover, we establish a novel and efficient numerical resolution framework combining a path-following continuation technique by Asymptotic Numerical Method (ANM) and a discretization by a spectral method. The main advantages of this framework include the generality for both compressible and incompressible materials, ease of programming, high precision and efficient continuation predictor. Based on the proposed approach, effect of different incompressible constitutive models on the post-buckling response is investigated, which shows that restabilization points and wrinkling amplitudes are quantitatively influenced. However, for compressible materials, Poisson's ratio plays a critical role in the wrinkling and restabilization behavior. We find that smaller Poisson's ratio makes later onset of wrinkling, lower amplitude and earlier disappearance of wrinkles. Besides, severe strain-stiffening phenomena are explored by accounting for phenomenological models such as Gent model and Gent-Gent model. Efficiency and accuracy of the proposed modelling and resolution framework were examined by comparing with some benchmarks.

C. Fu, T. Wang, F. Xu, Y. Huo, M. Potier-Ferry

J. Mech. Phys. Solids, https://doi.org/10.1016/j.jmps.2018.11.005

https://doi.org/10.1039/C8CP01191E We investigate the effect of varying carbon nanotube (CNT) size on the desalination performance through slit confinements formed by horizontally aligned CNTs stacked on top of one another. By increasing the CNT size, the results obtained from this study indicate a corresponding increase in the water flow rate, accompanied by a slight reduction in salt rejection performance. However, due to the increase in the membrane area with CNT size, the permeability performance is observed to reduce as the CNT size increases. Nevertheless, a comparison with nanoporous 2D membranes shows that the permeability of an outer-wall CNT slit membrane remains significantly higher for all CNT sizes considered. This indicates that precise dimensions of the CNTs are not highly crucial for achieving ultra-high permeability performance in such membranes, as long as the critical slit size is maintained. In-depth analytical studies were further conducted to correlate the influence of curvature effects due to increasing CNT size on the flow characteristcis of the outer-wall CNT membrane. These include the analysis of the measured velocity profiles, oxygen density mapping, potential of mean force profile and friction profile. The present numerical results demonstrate the superb desalination performance of the outer-wall CNT slit membrane, regardless of the size of CNTs used. In addition, an extensive analysis conducted provides detailed characterization of how the curvature affects flow across outer-wall CNTs, and can be used to guide future design and fabrication for experimental testing.

(in Journal of Elasticity)

A continuum mechanical framework is developed for determining a) the class of stress-free deformed shapes and corresponding director distributions on the undeformed configuration of a nematic glass membrane that has a prescribed spontaneous stretch field and b) the class of undeformed configurations and corresponding director distributions on it resulting in a stress-free given deformed shape of a nematic glass sheet with a prescribed spontaneous stretch field. The proposed solution rests on an understanding of how the Lagrangian dyad of a deformation of a membrane maps into the Euleriandyad in three dimensional ambient space. Interesting connections between these practical questions of design and the mathematical theory of isometric embeddings of manifolds, deformations between two prescribed Riemannian manifolds, and the slip-line theory of plasticity are pointed out.

http://rainbow.ku.dk/projects/

3 projects available at University of Luxembourg in collaboration with companies in the health sector

Breast cancer treatment simulator: http://rainbow.ku.dk/projects/esr6/

Biological Membrane Cutting: http://rainbow.ku.dk/projects/esr8/

3D Cutting simulation in soft tissue: http://rainbow.ku.dk/projects/esr12/

please contact stephane dot bordas @ gmail dot com for details and copy marie @ marois @ uni Dot lu

including your CV, list of references and a cover letter stating your interest and indicating the number of the PhD studentship you are interested in.

Regards,

Stéphane

http://orbilu.uni.lu/handle/10993/16438 http://orbilu.uni.lu/bitstream/10993/16438/1/2014_NURBSbasedExplicit_Mem...

NURBS-based isogeometric analysis was first extended to thin shell/membrane structures which allows for
finite membrane stretching as well as large deflection and bending strain. The assumed non-linear
kinematics employs the Kirchhoff-Love shell theory to describe the mechanical behaviour of thin to ultrathin
structures. The displacement fields are interpolated from the displacements of control points only, and
no rotational degrees of freedom are used at control points. Due to the high order Ck (k ≥ 1) continuity of
NURBS shape functions the Kirchhoff-Love theory can be seamlessly implemented. An explicit time
integration scheme is used to compute the transient response of membrane structures to time-domain
excitations, and a dynamic relaxation method is employed to obtain steady-state solutions. The versatility
and good performance of the present formulation is demonstrated with the aid of a number of test cases,
including a square membrane strip under static pressure, the inflation of a spherical shell under internal
pressure, the inflation of a square airbag and the inflation of a rubber balloon. The mechanical contribution
of the bending stiffness is also evaluated.