Etude des mécanismes d'accélération des flammes se propageant depuis l'extrémité fermée vers l'extrémité ouverte de tubes horizontaux de longueur variable

POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Replacing Detonation by Compressed Balloon Approaches in Finite Element Models

International audienceThe evaluation of blast effects from malicious or accidental detonation of an explosive device is really challenging especially on large buildings. Indeed, the time and space scales of the explosion together with the chemical reactions and fluid mechanics make the numerical model really difficult to achieve acceptable structural design. Nevertheless, finite element methods and especially Arbitrary Lagrangian Eulerian (ALE) have been extensively used in the past few decades with some simplifications. Among them, the replacement of the explosive event by a compressed balloon of detonation products has been proven useful in numerous different situations. Unfortunately, the ALE algorithm does not achieve a proper energy balance through the numerical integration of the discrete scheme; this important drawback is not compensated by the use of the classical compressed balloon approach. The paper focuses on increasing the radius of the equivalent ideal gas balloon in order to achieve better energy balance and thus better results at later stages of the blast wave propagation

Modelling of micro-inertia effects in closed-cell foams with application to acoustic and shock wave propagation

International audienceA continuum approach is proposed to describe micro-inertia effects in closed-cell foams using a micromechanical method. An initially spherical unit-cell was considered and the influence of inertia at the unit-cell level was characterised with the use of a dynamic homogenisation technique. The contribution of micro-inertia appears in the form of a dynamic component of the macroscopic stress. A closed-form expression of the dynamic stress was obtained. The proposed modelling was applied to acoustic and shock wave propagation. In both cases, the influence of micro-inertia was found to be significant. The obtained results are in good agreement with existing data of the literature, provided by micromechanically accurate finite element computations and experiments. The proposed model is aimed to enhance continuum models of foam materials by taking into account the contribution of micro-inertia

Impact of a shock wave on a heterogeneous foam film

International audienceLiquid foams are, amongst other applications, used to mitigate shock waves. This aspect has received considerable attention at the macroscopic scale. However, the interaction between foam films and shock waves is still poorly understood and may be an important missing local information to build mitigation models. In this paper, we experimentally identify a new process leading to the foam film rupture, which dominates when the film thickness is sufficiently heterogeneous. Using a two-thickness film with a sharp and localised thickness gradient, we record the deformation of the interface between the thick and the thin parts. We observe the growth of an excess liquid area in the thin part and establish an analytical model and scaling laws which account for this phenomenon. Our results in this ideal configuration are consistent with actual rupture processes at stake in heterogeneous foam films

Mitigation of underwater blast by diphasic barrier

Journées scientifiques : IPSF 2011 BERNE, Suiss

A constitutive model for the compressive response of metallic closed-cell foams including micro-inertia effects

Metallic foams have known a keen interest in the last decades. Their ability to undergo very large deformations while transmitting low stress levels make them capable of performing functions of protective layers against intense loadings and of energy absorbers, for instance. The behaviour of metal foams varies considerably between quasi-static and dynamic regimes. Those differences can be linked to the strain-rate sensitivity of the skeleton material and to micro-inertial effects (induced by the crushing of the foam cells). In the present work, a micromechanical model has been developed to take into account micro-inertia effects on the macroscopic behaviour of closed-cell foams under dynamic loading conditions. The proposed modelling is based on the dynamic homogenisation procedure introduced by Molinari and Mercier (J. Mech. Phys. Solids 49 (2001) 1497–1516). Within this framework, the macrostress is the sum of two terms. The first one is a static stress, that can be described with any existing model of metal foam. The second contribution is a dynamic stress related to micro-inertia effects. Considering an initially spherical shell as a Representative Volume Element (RVE) of the foam material, a closed-form expression of the dynamic stress was obtained. The proposed modelling was applied to shock propagation in aluminium foams (it should however be noted that the present theory is not restricted to uniaxial deformation but can be applied to arbitrary loadings). From experimental data of the literature, it is observed that incorporating micro-inertia effects allows one to achieve a better description of the foam shock response. This indicates that micro-inertia may have a significant influence on the dynamic behaviour of metallic foams

Shockwave / foam film interaction (presenter Q. Raimbaud)

International audienc

Modélisation du comportement de mousses métalliques sous choc. Journées du groupe de travail

International audienc

A constitutive model for the compressive response of metallic closed-cell foams including micro-inertia effects

Metallic foams have known a keen interest in the last decades. Their ability to undergo very large deformations while transmitting low stress levels make them capable of performing functions of protective layers against intense loadings and of energy absorbers, for instance. The behaviour of metal foams varies considerably between quasi-static and dynamic regimes. Those differences can be linked to the strain-rate sensitivity of the skeleton material and to micro-inertial effects (induced by the crushing of the foam cells). In the present work, a micromechanical model has been developed to take into account micro-inertia effects on the macroscopic behaviour of closed-cell foams under dynamic loading conditions. The proposed modelling is based on the dynamic homogenisation procedure introduced by Molinari and Mercier (J. Mech. Phys. Solids 49 (2001) 1497–1516). Within this framework, the macrostress is the sum of two terms. The first one is a static stress, that can be described with any existing model of metal foam. The second contribution is a dynamic stress related to micro-inertia effects. Considering an initially spherical shell as a Representative Volume Element (RVE) of the foam material, a closed-form expression of the dynamic stress was obtained. The proposed modelling was applied to shock propagation in aluminium foams (it should however be noted that the present theory is not restricted to uniaxial deformation but can be applied to arbitrary loadings). From experimental data of the literature, it is observed that incorporating micro-inertia effects allows one to achieve a better description of the foam shock response. This indicates that micro-inertia may have a significant influence on the dynamic behaviour of metallic foams

Foam film / shock wave interaction

International audienc