On the behaviour of lung tissue under tension and compression

Lung injuries are common among those who suffer an impact or trauma. The relative severity of injuries up to physical tearing of tissue have been documented in clinical studies. However, the specific details of energy required to cause visible damage to the lung parenchyma are lacking. Furthermore, the limitations of lung tissue under simple mechanical loading are also not well documented. This study aimed to collect mechanical test data from freshly excised lung, obtained from both Sprague-Dawley rats and New Zealand White rabbits. Compression and tension tests were conducted at three different strain rates: 0.25, 2.5 and 25 min−1. This study aimed to characterise the quasi-static behaviour of the bulk tissue prior to extending to higher rates. A nonlinear viscoelastic analytical model was applied to the data to describe their behaviour. Results exhibited asymmetry in terms of differences between tension and compression. The rabbit tissue also appeared to exhibit stronger viscous behaviour than the rat tissue. As a narrow strain rate band is explored here, no conclusions are being drawn currently regarding the rate sensitivity of rat tissue. However, this study does highlight both the clear differences between the two tissue types and the important role that composition and microstructure can play in mechanical response

Homogenization of a nitinol stent-graft to simulate its deployement in an abdominal aortic aneurysm

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Technique d'homogénéisation pour un stent en cas de d'AAA

International audienceThis studie prsent an homogeneization technic usefull for stent prosthesis (use in case of AAA) to reduce calculation time and make possible the numerical simulation in real time by means of per-operatory imagesCette étude présente une méthode d'homogénéisation appliquée à des endopro-thèses (utilisées en cas d'AAA) afin de réduire le temps de calcul de ces structures complexes et rendre la simulation numérique de leur comportement en temps réel possible grâce à des images per-opératoires

Numerical modeling of bra wear during running

International audienceNumerical modelling of bras and their influence on breasts during sport could be a valuable tool for bra designers as it could avoid the development of prototypes and help improving the performances of bras. Such a model requires a model for the breasts and for the bra. Models of breasts are available in the literature but they are based on MRI data that are expensive and heavy to segment and mesh. One of the main issues to develop a breast numerical model is to define a reference state for the breast without gravity, to avoid errors in the evaluation of stresses during sport. Rajagopal et al. used water to cancel the effect of gravity on a part of the breast and define the reference state; this idea is followed in the present work. The present work is focused on modelling female breasts, simulating brawear and investigating the influence of the bra on stresses and strains in the breast. A particular objective of this work is to provide a model that can run fast enough on a regular computer, so that it is convenient to use for industrial and commercial purposes

Une formulation monolithique d'interaction fluide-structure pour la co-simulation appliquée au piston 1D

International audienceCe résumé étendu a pour but de présenter une méthode de couplage pour les problèmes d'in-teraction fluide-structure, dont le but est d'être conservatif et d'utiliser des méthodes de calcul usuelles pour chaque sous-domaine fluide et structure. Ainsi le couplage est basé sur une formulation monoli-thique de la conservation de l'énergie et est résolu par un algorithme de co-simulation. Le but final est de coupler deux codes commerciaux existants. La méthode proposée est validée sur le cas test du piston 1D, en mono et multi-échelle en temps

A monolithic formulation of fluid-structure interaction for the co-simulation: Application to the piston problem

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Une formulation monolithique d'interaction fluide-structure pour la co-simulation appliquée au piston 1D

International audienceCe résumé étendu a pour but de présenter une méthode de couplage pour les problèmes d'in-teraction fluide-structure, dont le but est d'être conservatif et d'utiliser des méthodes de calcul usuelles pour chaque sous-domaine fluide et structure. Ainsi le couplage est basé sur une formulation monoli-thique de la conservation de l'énergie et est résolu par un algorithme de co-simulation. Le but final est de coupler deux codes commerciaux existants. La méthode proposée est validée sur le cas test du piston 1D, en mono et multi-échelle en temps

Numerical identification method for the non-linear viscoelastic compressible behavior of soft tissue using uniaxial tensile tests and image registration – Application to rat lung parenchyma

International audienceThis paper presents an improved identification method of the constitutive properties of lung parenchyma. We aim to determine the non-linear viscoelastic behavior of lung parenchyma with a particular focus on the compressible properties - i.e. the ability to change volume. Uniaxial tensile tests are performed on living precision-cut rat lung slices. Image registration is used to compute the displacement field at the surface of the sample. The constitutive model consists of a hyperelastic potential split into volumetric and isochoric contributions and a viscous contribution. This allows for the description of the experimentally observed hysteresis loop. The identification is performed numerically: each test is simulated using the realistic geometry of the sample; the difference between the measured and computed displacements is minimized with an optimization algorithm. We compare several hyperelastic potentials and we can determine the most suitable law for rat lung parenchyma. An exponential potential or a polynomial potential with a first order term and a third or higher order term give similarly satisfactory results. The identified parameters are: for the volumetric contribution: κ =7.25e4 Pa, for the exponential form: k1=4.34e3 Pa, k2=5.92, for the polynomial form: C1=2.87e3 Pa, C3=3.83e4 Pa. The identification of the time parameter for the viscous contribution shows that it depends on the loading frequency (0.2 Hz: τ =0.257 s, 0.4 Hz: τ=0.123 s, 0.8 Hz: τ=0.050 s). Adding a viscous contribution significantly increases the accuracy of the identification

A selective mass scaling method for shear wave propagation analyses in nearly incompressible materials

International audienceThis paper describes a selective mass scaling (SMS) method which is designed for the analysis of wave propagation problems in nearly incompressible materials. The incompressibility of materials leads to a high value of the compressional wave speed which makes the time step extremely small in explicit time integration method. The proposed SMS method selects the eigenfrequencies related to volumetric deformation modes to decrease them, while it keeps the shear eigenmodes unchanged. This makes the time step no longer limited by the compressional wave speed but by the shear wave speed. A significant reduction of CPU time is obtained with a good accuracy for transient problems in small strains on free or largely prestressed media

Simulation of nonlinear transient elastography: finite element model for the propagation of shear waves in homogeneous soft tissues

International audienceIn this study, visco-hyperelastic Landau's model which is widely used in acoustical physic field is introduced into a finite element formulation. It is designed to model the non-linear behaviour of finite amplitude shear waves in soft solids, typically, in biological tissues. This law is employed in finite element models based on elastography experiments reported in [1], the simulations results show a good agreement with the experimental study : it is observed in both that a plane shear wave generates only odd harmonics and a nonplane wave generates both odd and even harmonics in the spectral domain. In the second part, a parametric study is carried out to analyze the influence of different factors on the generation of odd harmonics of plane wave. A quantitative relation is fitted between the odd harmonic amplitudes and the non-linear elastic parameter of Landau's model, which provides a practical guideline to identify the nonlinearity of homogeneous tissues using elastography experiment