Publications

2017

• An augmented iterative method for identifying a stress-free reference configuration in image-based biomechanical modeling
  
  • Rausch Manuel K.
  • Genet Martin
  • Humphrey Jay D.
  Journal of Biomechanics, Elsevier, 2017, 58, pp.227 - 231. Continuing advances in computational power and methods have enabled image-based biomechanical modeling to become a crucial tool in basic science, diagnostic and therapeutic medicine, and medical device design. One of the many challenges of this approach, however, is the identification of a stress-free reference configuration based on in vivo images of loaded and often prestressed or residually stressed soft tissues and organs. Fortunately, iterative methods have been proposed to solve this inverse problem, among them Sellier’s method. This method is particularly appealing for it is easy to implement, convergences reasonably fast, and can be coupled to nearly any finite element package. However, by means of several practical examples, we demonstrate that in its original formulation Sellier’s method is not optimally fast and may not converge for problems with large deformations. Fortunately, we can also show that a simple, inexpensive augmentation of Sellier’s method based on Aitken’s delta-squared process can not only ensure convergence but also significantly accelerate the method. (10.1016/j.jbiomech.2017.04.021)
  DOI : 10.1016/j.jbiomech.2017.04.021
• Coupling damage and plasticity for a phase-field regularisation of brittle, cohesive and ductile fracture: one-dimensional examples
  
  • Alessi Roberto
  • Marigo Jean-Jacques
  • Maurini Corrado
  • Vidoli Stefano
  International Journal of Mechanical Sciences, Elsevier, 2017. Plasticity and damage are two fundamental phenomena in nonlinear solid mechanics associated to the development of inelastic deformations and the reduction of the material stiffness. Alessi et al. [4] have recently shown, through a variational framework, that coupling a gradient-damage model with plasticity can lead to macroscopic behaviours assimilable to ductile and cohesive fracture. Here, we further expand this approach considering specific constitutive functions frequently used in phase-field models of brittle fracture. A numerical solution technique of the coupled elasto-damage-plasticity problem, based on an alternate minimisation algorithm, is proposed and tested against semi-analytical results. Considering a one-dimensional traction test, we illustrate the properties of four different regimes obtained by a suitable tuning of few key constitutive parameters. Namely, depending on the relative yield stresses and softening behaviours of the plasticity and the damage criteria, we obtain macroscopic responses assimilable to (i) brittle fracturèfracturè a la Griffith, (ii) cohesive fractures of the Barenblatt or Dugdale type, and (iii) a sort of cohesive fracture including a depinning energy contribution. The comparisons between numerical and analytical results prove the accuracy of the proposed numerical approaches in the considered quasi-static time-discrete setting, but they also emphasise some subtle issues occurring during time-discontinuous evolutions. (10.1016/j.ijmecsci.2017.05.047)
  DOI : 10.1016/j.ijmecsci.2017.05.047
• Coupling schemes for the FSI forward prediction challenge: comparative study and validation
  
  • Landajuela Mikel
  • Vidrascu Marina
  • Chapelle Dominique
  • Fernández Miguel Angel
  International Journal for Numerical Methods in Biomedical Engineering, John Wiley and Sons, 2017, 33 (4), pp.e02813. This paper presents a numerical study in which several partitioned solution procedures for incompressible fluid-structure interaction are compared and validated against the results of an experimental FSI benchmark. The numerical methods discussed cover the three main families of coupling schemes: strongly coupled, semi-implicit and loosely coupled. Very good agreement is observed between the numerical and experimental results. The comparisons confirm that strong coupling can be efficiently avoided, via semi-implicit and loosely coupled schemes, without compromising stability and accuracy. (10.1002/cnm.2813)
  DOI : 10.1002/cnm.2813
• Numerical modeling of the acoustic wave propagation across an homogenized rigid microstructure in the time domain
  
  • Lombard Bruno
  • Maurel Agnes
  • Marigo Jean-Jacques
  Journal of Computational Physics, Elsevier, 2017, 335, pp.558-577. Homogenization of a thin micro-structure yields effective jump conditions that incorporate the geometrical features of the scatterers. These jump conditions apply across a thin but nonzero thickness interface whose interior is disregarded. This paper aims (i) to propose a numerical method able to handle the jump conditions in order to simulate the homogenized problem in the time domain, (ii) to inspect the validity of the homogenized problem when compared to the real one. For this purpose, we adapt the Explicit Simplified Interface Method originally developed for standard jump conditions across a zero-thickness interface. Doing so allows us to handle arbitrary-shaped interfaces on a Cartesian grid with the same efficiency and accuracy of the numerical scheme than those obtained in an homogeneous medium. Numerical experiments are performed to test the properties of the numerical method and to inspect the validity of the homogenization problem. (10.1016/j.jcp.2017.01.036)
  DOI : 10.1016/j.jcp.2017.01.036
• Analyse thermomécanique des problèmes de fissure fixe sous chargement dynamique
  
  • Soumahoro Zoumana
  • Maigre Hubert
  Comptes Rendus. Mécanique, Académie des sciences (Paris), 2017, 345, pp.221 - 238. L’objectif de ce travail est d’étudier le couplage thermomécanique dans les mécanismes de rupture dynamique pour une fissure fixe sous chargement dynamique. (10.1016/j.crme.2017.01.002)
  DOI : 10.1016/j.crme.2017.01.002
• Caractérisation et modélisation de l'alliage Ti-6Al-4V sous chargement dynamique complexe
  
  • Sotto M. Ruiz De
  • Longère Patrice
  • Doquet V.
  • Papasidero J.
  , 2017.
• Boundary integral equation methods for elastic and plastic problems
  
  • Bonnet Marc
  , 2017, pp.719-749. This chapter deals with formulations based on boundary integral equations (BIEs) for elastic and plastic problems. After a brief review of the basic integral identities of solid mechanics and issues associated with the singular character of the fundamental solutions, the collocation and symmetric Galerkin BIE formulations and the associated boundary element methods (BEMs) are presented in their conventional form where the complete matrix equation is set up using numerical integration and stored. This approach being inadequate for large problem sizes, fast solution techniques are then reviewed, with emphasis on the fast multipole method. Next, BEMs in both collocation and symmetric Galerkin form are described for fracture mechanics and small-strain elastoplasticity. The treatment of the hypersingular integrals arising in the integral representation of tractions on the crack surface or of strains at potentially plastic interior points is discussed, along with other issues. Shape sensitivity analysis techniques are also presented, based on either the direct differentiation of the primary elastic BIE or an adjoint solution. Finally, the symmetric Galerkin BIE is used to define a symmetric formulation for BEM–FEM coupling. (10.1002/9781119176817.ecm2047)
  DOI : 10.1002/9781119176817.ecm2047
• Patient-specific modeling for left ventricular mechanics using data-driven boundary energies
  
  • Asner Liya
  • Hadjicharalambous Myrianthi
  • Chabiniok Radomir
  • Peressutti Devis
  • Sammut Eva
  • Wong James
  • Carr-White Gerald
  • Razavi Reza
  • King Andrew D.
  • Smith Nicolas P.
  • Lee Jack
  • Nordsletten D
  Computer Methods in Applied Mechanics and Engineering, Elsevier, 2017, 314, pp.269-295. Supported by the wide range of available medical data available, cardiac biomechanical modeling has exhibited significant potential to improve our understanding of heart function and to assisting in patient diagnosis and treatment. A critical step towards the development of accurate patient-specific models is the deployment of boundary conditions capable of integrating data into the model to enhance model fidelity. This step is often hindered by sparse or noisy data that, if applied directly, can introduce non-physiological forces and artifacts into the model. To address these issues, in this paper we propose novel boundary conditions which aim to balance the accurate use of data with physiological boundary forces and model outcomes through the use of data-derived boundary energies. The introduced techniques employ Lagrange multipliers, penalty methods and moment-based constraints to achieve robustness to data of varying quality and quantity. The proposed methods are compared with commonly used boundary conditions over an idealized left ventricle as well as over in vivo models, exhibiting significant improvement in model accuracy. The boundary conditions are also employed in in vivo full-cycle models of healthy and diseased hearts, demonstrating the ability of the proposed approaches to reproduce data-derived deformation and physiological boundary forces over a varied range of cardiac function. (10.1016/j.cma.2016.08.002)
  DOI : 10.1016/j.cma.2016.08.002
• Imposed curvature of an elastic-plastic strip: application to simulation of coils
  
  • Weisz-Patrault Daniel
  • Ehrlacher Alain
  Mechanics & Industry, EDP Sciences, 2017, 18 (2). – This work is part of the framework of a fast modeling of winding aiming at improving knowledge of residual stress evolution in steel strips and therefore their flatness during the coiling process. An exact analytical solution of an elastic-plastic strip with isotropic hardening at finite strains under an imposed transformation of curvature is developed. Issues related to flow rules for non-differentiable yield functions (Tresca) have been broached and a unique solution is obtained. The equivalence for this transformation, between von Mises and Tresca yield functions is demonstrated. This solution contributes to an efficient model by terms of computation times that aims at simulating coiling by taking into account inelastic deformations and enabling parametric studies in order to improve the process. (10.1051/meca/2016038)
  DOI : 10.1051/meca/2016038