Experimental and Numerical Analyses of 3D Interlock Composite Preforming

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Full-field strain measurements in textile deformability studies

Full-field strain measurements are applied in studies of textile deformability during composite processing: (1) in testing of shear and tensile deformations of textiles (picture frame, bias and biaxial extension test) as an ‘‘optical extensometer’’, allowing accurate assessment of the sample deformation, which may differ significantly from the deformation applied by the testing device; (2) to study mechanisms of the textile deformation on the scale of the textile unit cell and of the individual yarns (meso- and micro-scale full-field strain measurements); (3) to measure the 3D-deformed shape and the distribution of local deformations (e.g., shear angles) of a textile reinforcement after draping, providing input data for the validation of material drape models and for the prediction of the consolidated part performance via structural finite element analysis. This paper discusses these three applications of the full-field strain measurements, providing examples of studies of deformability of woven (glass, glass/PP) and non-crimp (carbon) textile reinforcements. The authors conclude that optical full-field strain techniques are the preferable (sometimes the only) way of assuring correct deformation measurements during tensile or shear tests of textile.status: publishe

Study of solutions to optimize the extraction of hemp fibers for composite materials

Fibres from hemp stems can be extracted through different mechanical processes following dew or water retting etc. Extraction processes generally have a significant impact on mechanical and morphological properties of the fibres. In this study, hemp fibres are extracted following three different ways. In the first route hemp fibres are extracted from FUTURA 75 variety stems by performing scutching, hackling and microwave degumming. A second batch of fibres of the same variety was extracted by scutching and hackling after an initial microwave degumming treatment. In the third route, the same variety of hemp fibres are extracted from dew retted stems grown at Piacenza (Italy). Finally, the mechanical properties of single fibres as well as the fineness of technical fibres of all types of extracted fibres are evaluated and compared and the interest of the microwave degumming for hemp stem is evaluated

Comparing flax and hemp fibres yield and mechanical properties after scutching/hackling processing

Increasing the production of high-performance natural fibres that minimise their impact on the environment is a challenge that flax (Linum usitatissinum L.) cannot address alone. In flax traditional production territories, hemp (Cannabis sativa L.) can be a complementary source of high added value fibres if their yield of long line fibres can be maximised to levels equivalent to the one of flax. The objective of the present work was to establish process parameters maximising the long line fibre yield using flax dedicated scutching and hackling devices. A lab-scale scutching/hackling device was used to establish sets of process parameters which best improve the long fibre scutching yield and as a consequence minimise the production of tow fibres. Decreases in straw processing transfer and beating speeds during scutching were necessary so that to be less aggressive on the straw and fibres. Very high long fibre yields were obtained after scutching and hackling at the laboratory scale (18 % of the hemp straw mass). These very high results, combined to high straw yield production in the field indicate that hemp can be a very productive source of high-performance fibres as these ones showed tensile properties completely suitable for a textile use as well as for load bearing composite materials. If the potential of high production yields and high mechanical and morphological properties was demonstrated at the lab-scale, this one should be improved at the industrial scale. Suggestions to reach this goal are provided to prevent too high transformation of long fibres into tows and to keep the mechanical potential maximum. When using optimised parameters and a lab-scale scutching/hackling device, it was demonstrated that hemp has the potential for providing equivalent amounts of long fibres per hectare than flax with tensile properties about 20 % lower than the ones of flax

Influence of industrial processing parameters on the effective properties of long aligned European hemp fibres in composite materials

Hemp is a sustainable source of natural fibres that can contribute to meet the increasing demand for technical applications in the textile and the composite sectors. Continuous reinforcements can be produced using the existing flax machinery, initially developed for textile purposes. To achieve competitive and economically viable fibre yields and a fibre quality suitable for secondary processing and composite application, hemp needs to be adequately selected and prepared and the flax machinery and settings have to be adapted to the hemp specificities. In this context, this paper studies the influence of agronomic features and processing stages and settings on the effective tensile properties of fibres extracted from two hemp varieties determined using impregnated fibre bundle tests. Results show that the effective properties of fibres are maintained and even improved during processing, in particular during the hackling and stretching steps. Hemp can achieve properties comparable to high quality long flax fibres

Characterization of mechanical behavior of woven fabrics: Experimental methods and benchmark results

Textile composites made of woven fabrics have demonstrated excellent mechanical properties for the production of high specific-strength products. Research efforts in the woven fabric sheet forming are currently at a point where benchmarking will lead to major advances in understanding both the strengths and the limitations of existing experimental and modeling approaches. Test results can provide valuable information for the material characterization and forming process design of woven composites if researchers know how to interpret the results obtained from varying test methods appropriately. An international group of academic and industry researchers has gathered to design and conduct benchmarking tests of interest to the composite sheet forming community. Shear deformation is the dominative deformation mode for woven fabrics in forming; therefore, trellis-frame (picture-frame) and bias-extension tests for both balanced and unbalanced fabrics have been conducted and compared through this collaborative effort. Tests were conducted by seven international research institutions on three identical woven fabrics. Both the variations in the setup of each research laboratory and the normalization methods used to compare the test results are presented and discussed. With an understanding of the effects of testing variations on the results and the normalization methods, numerical modeling efforts can commence and new testing methods can be developed to advance the field. (c) 2008 Elsevier Ltd. All rights reserved