• Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur
  
• Sciences de l'ingénieur/Matériaux
  
• Physique/Physique/Optique
  
• Chimie/Polymères
  
• Chimie/Matériaux
  
• Sciences du Vivant/Biologie végétale/Botanique
  
• Physique/Mécanique/Biomécanique
  
• Physique/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Mécanique/Vibrations
  
• Physique/Mécanique/Vibrations
  
• Sciences de l'ingénieur/Mécanique
  

The aim of this paper is to describe the dynamic behavior of biaxial glass fiber reinforced laminate composites under low velocity impact test through finite element modelling. Experimental investigations by impact test performed using an instrumented drop weight testing machine were conducted on three-point bending composite samples in order to assess their impact damage resistance. Moreover, the experimental setup allowed the visualization of real-time damage progression of the impacted laminate composite via high-speed camera Phantom V2512 enabling to capture 83000 frames per second. Dynamic strain fields were extracted by Digital Image Correlation (DIC) method. Based on the experimental results, a numerical study of the impacted specimens was developed as a user subroutine VUMAT integrated to ABAQUS/Explicit in order to precisely capture the progressive dynamic failure of the laminate composite under impact test. In the proposed model, the damage and failure of each ply are accounted by a Hashin 3D damage-based behavior, and a cohesive zone model is employed to capture the onset and progression of inter-laminar delamination. A good experimental-numerical correlation was obtained for peak force and failure modes.

Measuring and understanding the swelling and softening behaviour of plant fibres under controlled humidity in relation with their moisture content are critical for their valorization in composites applications. Indeed, they directly influence the processing and in-service behaviour of biocomposites. The aim of this work is to characterize, under controlled hygro- and hydrothermal conditions (from 20% to 73% RH and in immersion), the moisture content, dimensional variations and mechanical behaviour of natural fibre bundles from various botanical origins with contrasting biochemical and structural characteristics. Automated laser scanning cross-sectional measurements and micro-tensile tests conducted either in a climate chamber or in an immersion cell allowed measuring cross-dimensional variations and tensile properties of the fibre bundles in relation with their moisture content determined by DVS and WRV. These analyses lead to determine the surface hygro- and hydroexpansion coefficients of the different natural fibre bundles in relation with the structural characteristics of the cell walls [1]. The softening effect of water on the cell walls and resulting loss of stiffness and strength of fibre bundles is also discussed in relation with water sorption and swelling [2]. These results constitute key data for the predictive modelling of “in-service” mechanical behaviour of biocomposites.

Current environmental concerns push towards more sustainable and local practices for biomass production. In this regard, agroforestry has been highlighted by researchers and policies as a highly efficient approach for carbon sequestration (between 1.5 and 4 t C/ha/year), and a sustainable alternative to deforestation with many agricultural benefits: deeper rooting of trees in soil, enhanced biomass productivity, crop fertilization... Agroforestry implies regular branch cuts that are processed into wood chips and mostly used as energy wood or soil mulching. New higher added-value chains could be considered such as reinforcements or specific molecules for bio-based materials and chemistry. Besides, since 90’s, Wood-Plastic Composites (WPCs) have experienced significant growth, particularly in building (decking & siding), and constitute the largest share of bio-based composites developed at an industrial scale. Nevertheless, the quality of WPCs and variability in their performance are major technological issues for their implementation in industrial applications. This could be related to the difficulty in tracing the various origin of wood fillers as well as the different processing steps, from wood drying and defibration process to composite manufacturing, that are not well controlled. Indeed, numerous interdependent parameters govern the final properties of WPCs, such as biochemical composition, presence of metallic and chemical contaminants (binders, wood treatment residues, varnishes, etc.), (micro)structure, thermal stability, mechanical properties of wood fillers, and the control of their milling/granulometry and further processing into composite materials. In this context, the development of quality-controlled agroforestry wood fillers in terms of granulometry (size and shape factor), chemical composition and physical (microstructure, mechanical) properties is therefore strategic for their implementation in wood-based products. This work investigates and evidences the influence of wood species (poplar, oak, walnut, chestnut)) and filler size and shape on the microstructure and mechanical properties of polypropylene (PP) / wood composites manufactured by extrusion/injection moulded. Moreover, wood from three recovery platforms in Brittany (mix of several species) was also investigated to evaluate the potential of existing agroforestry feedstocks.

High speed imaging is applied for drop test on composite samples. The effect of optical blur on image correlation accuracy is described. Blur magnitude is tuned by decreasing the exposure time (at constant sensor sensitivity) for the same drop test series on flyspecked composite plates, while focus, aperture and 1:1 magnification are kept constant. Frame rate (80-20kfps) and lighting are changed while keeping the same image contrast. Results show correlation quality is already altered with subpixel blur. This study enables to define blur criterion in high-speed imaging and completes study about sampling rate effect in time resolved image correlation by high-speed imaging.