Modelling of low-energy/low-velocity impact on Nomex honeycomb sandwich structures with metallic skins

In the aircraft industry, manufacturers have to decide quickly whether an impacted sandwich needs repairing or not. Certain computation tools exist at present but they are very time-consuming and they also fail to perfectly model the physical phenomena involved in an impact. In a previous publication, the authors demonstrated the possibility of representing the NomexTM honeycomb core by a grid of nonlinear springs and have pointed out both the structural behaviour of the honeycomb and the influence of core-skin boundary conditions. This discrete approach accurately predicts the static indentation on honeycomb core alone and the indentation on sandwich structure with metal skins supported on rigid flat support. In this study, the domain of validity of this approach is investigated. It is found that the approach is not valid for sharp projectiles on thin skins. In any case, the spring elements used to model the honeycomb cannot take into account the transverse shear that occurs in the core during the bending of a sandwich. To overcome this strong limitation, a multi-level approach is proposed in the present article. In this approach, the sandwich structure is modelled by Mindlin plate elements and the computed static contact law is implemented in a nonlinear spring located between the impactor and the structure. Thus, it is possible to predict the dynamic structural response in the case of low-velocity/low-energy impact on metal-skinned sandwich structures. A good correlation with dynamic experimental tests is achieved

Initiation and propagation mechanisms of progressive crushing in carbon-epoxy laminated plates

This article presents original experiments that enhance the understanding of the mechanisms that drive the progressive crushing of fiber-reinforced laminated composite materials and their energy absorption capability. An innovative experimental fixture has been created in order to obtain detailed monitoring of quasi-static and dynamic crushing of laminated plates. The fixture enables the development of a regular crushing front through the whole width of the plate, without parasite rupture modes, and the real-time observation of this front with a high speed camera. Results of experimental works on fabric and unidirectional Carbon-Epoxy laminated composite plates are exposed. The obtained crushing modes are analysed, their stability and energy-absorbing capability are discussed

Développement d'un modèle de l'écrasement progressif des composites stratifiés en dynamique

Grâce à un dispositif d'essai original d'écrasement de plaques composites, des modes d’écrasement élémentaires de stratifiés CFRP ont été observés et analysés pour des chargements statiques et dynamiques. Ces analyses ont permis de proposer un modèle éléments finis 2D explicite, avec modélisation de l'endommagement du matériau à l'échelle mésoscopique, pour la simulation du mode d’écrasement par évasement, avec une bonne corrélation entre modèle et expérience

Experimental and numerical study of the splaying mode crush of CFRP laminates

Thanks to an innovative plate crushing test fixture, elementary crushing modes of CFRP laminates have been observed and analysed for static and dynamic loading. These analyses enabled to propose a 2D explicit finite element model at mesoscale for the simulation of splaying mode, with a good correlation between model and test data

The GenTree Dendroecological Collection, tree-ring and wood density data from seven tree species across Europe

The dataset presented here was collected by the GenTree project (EU-Horizon 2020), which aims to improve the use of forest genetic resources across Europe by better understanding how trees adapt to their local environment. This dataset of individual tree-core characteristics including ring-width series and whole-core wood density was collected for seven ecologically and economically important European tree species: silver birch (Betula pendula), European beech (Fagus sylvatica), Norway spruce (Picea abies), European black poplar (Populus nigra), maritime pine (Pinus pinaster), Scots pine (Pinus sylvestris), and sessile oak (Quercus petraea). Tree-ring width measurements were obtained from 3600 trees in 142 populations and whole-core wood density was measured for 3098 trees in 125 populations. This dataset covers most of the geographical and climatic range occupied by the selected species. The potential use of it will be highly valuable for assessing ecological and evolutionary responses to environmental conditions as well as for model development and parameterization, to predict adaptability under climate change scenarios

Experimental and numerical study of the splaying mode crush of CFRP laminates

International audienceThanks to an innovative plate crushing test fixture, elementary crushing modes of CFRP laminates have been observed and analysed for static and dynamic loading. These analyses enabled to propose a 2D explicit finite element model at mesoscale for the simulation of splaying mode, with a good correlation between model and test data

Etude des mécanismes d’absorption d’énergie lors du crash de structures carbone-époxyde

Cette étude a pour but d’améliorer la compréhension des mécanismes de ruine progressive des composites stratifiés en compression dans le plan. Pour cela, un dispositif expérimental innovant a été développé pour constituer une base de donnée adaptée à la validation de méthodes numériques avancées. Il permet de stabiliser l’écrasement d’éprouvettes planes tout en laissant le front d’écrasement se développer sur toute leur largeur. On peut ainsi filmer la tranche de l’éprouvette au cours de l’essai pour corréler les images de l'endommagement avec la courbe caractéristique effort/déplacement. Une campagne expérimentale a été effectuée. Il s’agit de l’écrasement, en quasi-statique et en dynamique, de plaques de différents drapages de tissus équilibrés Carbone/Epoxyde, munies de différents triggers. L’analyse des données permet de montrer le lien entre la quantité d’énergie absorbée et le type de ruine observé. L’importance prépondérante de la géométrie du front d’écrasement dans les performances d’un absorbeur est établie