Anomalous diffusion mediated by atom deposition into a porous substrate

Constant flux atom deposition into a porous medium is shown to generate a dense overlayer and a diffusion profile. Scaling analysis shows that the overlayer acts as a dynamic control for atomic diffusion in the porous substrate. This is modeled by generalizing the porous diffusion equation with a time-dependent diffusion coefficient equivalent to a nonlinear rescaling of timeComment: 4 page

Lightning arc interaction with complex structure

Lightning is a natural and unpredictable phenomenon due to charge generation in clouds producing intense electrical field leading to flashes of extremely high current and high voltage pulses of few µs.In this context, aircrafts are subjected to the risk of being struck during flight and the lightning damage mechanism for carbon laminate aeronautical structure is a complex multi-physical phenomenon. In order to understand this phenomenon, it is of first importance to understand and predict the interaction of the lightning arc with the aircraft structure as it will change the energy deposition into the structure and the associated vaporization profile. This sudden vaporization is equivalent to an explosion on the surface of the composite. It is aimed here to evaluate this assertion through the comparison of experimental measurements of the vaporization radii for different painting configurations with numerical predictions

Lightning surface explosion impact study on damage generation into composite

Lightning damage mechanism for composite aircraft structure is a complex multi-physical phenomenon. The lightning current entering into the surface metallic protection and the carbon plies generates Joule’s effects and electromagnetic forces which both induce mechanical forces and surface explosion that produce a significant mechanical impact. The explosion of the lightning strike protection has been recorded through the measurement of the vaporization profile evolution in space and time using transparent glass epoxy substrates. In this paper, this profile is combined to shock wave model developed by the study of electric explosion on wire equivalent to web of ECF. The initial shock wave from the surface explosion has been injected into a mechanical model using Abaqus Explicit® with a pressure profile dependent on time and distance from lightning current injection. Results of the simulations are confronted with laboratory lightning tests for deflections and damages

Évaluation de la surpression générée par l'explosion électrique des protections foudre

Les avions, pouvant être frappés par la foudre durant leur vol, subissent un endommagement des structures en carbone dont le mécanisme est un phénomène multi-physique complexe. L'un des principaux contributeurs est la surpression générée par la vaporisation rapide de la protection métallique lors d’un coup foudre. Assimilée à un réseau de fil, la protection pourra être considérée comme un réseau de sources de surpression dépendantes de la densité de courant. Le but de l’étude est de valider un modèle de surpression liée à l’explosion de la protection foudre à partir de mesure d’onde de choc en laboratoire et de modèles d’explosion électrique

Lightning strike protection explosion and overpressure profile

Lightning is a natural and unpredictable phenomenon due to charge generation in clouds producing intense electrical field leading to flashes of extremely high current pulses of few µs. In this context, aircrafts are subjected to the risk of being struck during flight and the lightning damage mechanism for carbon laminate aeronautical structure is a complex multi-physical phenomenon. One of the main contributor is the overpressure generated by the quick vaporization of the metallic lightning strike protection that covers the composite aircraft surface in order to divert lightning current. The aim of this study is to validate the representation a each copper wire through the comparison of electro-thermal simulation of its vaporization with experimental tests measurements

Lightning damage assessment into composite based on surface explosion and fiber breakage

Lightning damage mechanism for composite aircraft structure is a complex multi-physical phenomenon. The lightning current entering into the surface metallic protection and the carbon plies generates Joule’s effects and electromagnetic forces which both induce mechanical forces and surface explosion that produce a significant mechanical impact. The explosion of the lightning strike protection has been recorded through the measurement of the vaporization profile evolution in space and time using transparent glass epoxy substrates. In this paper, this profile is combined to shock wave model developed by the study of electric explosion on wire equivalent to web of ECF. The second important phenomenon is fiber breakage due to current flow in CFRP. This has been assessed through specific lightning test measuring the current distribution between CFRP and LSP depending on the paint thickness. It is aimed is this paper to present the tests setup and observations. Those two loading components have been injected into a mechanical model using Abaqus Explicit® in order to assess the damage ignition and propagation in the composite thickness as a function of time. Simulations are similar to previous studies but use real tests measurements for the pressure evolution instead of an impulsion induced estimation. Results of the simulations are confronted with laboratory lightning tests. Deflection as functions of time has been measured thanks to stereo correlation devices. Simulated damage distributions are compared to post-mortem non-destructive and destructive measurement in the core of the composite plates

Banc d'essai pour la mesure d'échauffement du point de contact

Le point de contact présent dans le disjoncteur et l'interrupteur différentiel modulaires est le lieu où les lignes de courant se concentrent. Ce phénomène conduit à l'échauffement du point de contact, voire à sa fusion. Pour déterminer son échauffement et les conditions induisant une fusion, un gabarit de test a été conçu et réalisé. Nous pouvons ainsi quantifier l'influence des différents paramètres opératoires. Ce gabarit permet notamment la mesure de  la tension de contact qu'il est nécessaire de connaître pour le calcul de la température au centre de la striction à l'aide de la formule de Kohlrausch. Cette relation suppose un régime de fonctionnement statique malgré la nature  impulsionnelle du courant. Cet article décrit le banc de mesure mis au point, la justification du régime statique et les premières mesures effectuées

Estimation of the load produced by the electro-thermal behaviour of lightning strike protection layers on a composite panel

The lightning damage mechanism for carbon laminate aeronautical structure is a complex multi-physical phenomenon. The lightning current entering into the surface metallic protection, called LSP (Lightning Strike Protection) and the carbon plies generates Joule’s effects and magnetic forces which both induce mechanical forces and surface explosion that has a significant mechanical impact. In this paper, the focus is made on the contribution of the surface explosion. An electro-thermal model of the vaporization profile has been first validated with lightning test results for an accurate dynamic profile. In a second step an overpressure profile combined with the vaporization front has been implemented in a mechanical model. The deflection profiles of the mechanical model are in good correlation with measurements. The contribution of the explosion is the major contributor in the loading of composite panel. A next step will consist in the determination of the contribution of the CFRP (Carbon Fiber Reinforced Plastic) explosion in the first plies which initiates the damage in the composite by breaking the fibers

Numerical and experimental study of arc fault in aeronautical conditions

The use of electrical energy is constantly increasing in airplanes. This concerns needs in motor, actuators or those related to services for example. Naturally the electric energy-related risks increase. Arc discharges can appear with consequences that can be dramatic. The electrical constraints to which a plane is subject are not only internal. The aircraft are also regularly struck by lightning in-flight. Composite materials, increasingly used, make more difficult the management of these risks of lightning strikes. So the arc discharge is a concern in the aeronautical domain. This specific area imposes special conditions that do not exist in other areas where the arcs are present. Our intervention is intended to present these studies, with in the rest of this paper, references to two specific topics, the arc fault in the electric core of aircraft and damage to the composite by structure being struck by lightning

Numerical and experimental study of arc fault in aeronautical conditions

The use of electrical energy is constantly increasing in airplanes. This concerns needs in motor, actuators or those related to services for example. Naturally the electric energy-related risks increase. Arc discharges can appear with consequences that can be dramatic. The electrical constraints to which a plane is subject are not only internal. The aircraft are also regularly struck by lightning in-flight. Composite materials, increasingly used, make more difficult the management of these risks of lightning strikes. So the arc discharge is a concern in the aeronautical domain. This specific area imposes special conditions that do not exist in other areas where the arcs are present. Our intervention is intended to present these studies, with in the rest of this paper, references to two specific topics, the arc fault in the electric core of aircraft and damage to the composite by structure being struck by lightning