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The use of hemp fibers for the manufacturing of reinforcements for composite materials is not well common, despite a growing interest of natural fibers in this field of application. In addition to the choice of the type of fiber used, the choice of the type of reinforcement plays an important role in the final properties of the composite material. Unidirectional or woven fabrics are widely used as reinforcement to achieve advanced properties at the scale of composite, depending on the specifications of the final material. In this study, a quasi-unidirectional fabric and two woven fabrics (one balanced and one unbalanced in terms of fiber content) are studied to compare their properties at different levels: mechanical and preforming properties of the reinforcements in dry state and mechanical properties of composite materials reinforced by these fabrics. The objective is to highlight the advantages and drawbacks of both types of reinforcements (woven fabrics and quasi-unidirectional fabrics) in order to be able to select the most suitable reinforcement according to the specifications of the final composite part. As a result, the quasi-unidirectional reinforcement showed enhanced properties both at fabric and composite scale. These structures based on hemp fibers present promising properties that concur structures made of flax and already available on the market. [ABSTRACT FROM AUTHOR]

This experimental work concerns the study of the preforming of a specific highly double curved geometry with a triple point (case corner) by the sheet forming process using powdered interlock reinforcement (G1151®). Three different punches (square box, prism, tetrahedron) were used in this study, each of them presenting highly double curved geometry with a case corner. A specific sheet forming device specially designed for the preforming of textile reinforcement was used. The expected shapes with the three punches have been obtained with an optimized blank-holder pressure. No classical defaults such as wrinkling or yarn damage are present in the useful zone of the preforms. However, a new default, not observed for spherical or hemispherical shape has been identified. It concerns the out of plane buckling of yarns. This phenomenon not observed on the square box is visible on some faces and edges of the prismatic and tetrahedron shapes. For the square box, it is easily possible to control the orientation of the yarn within the preform in the faces, whereas this is not possible for triangular faces of the prismatic and tetrahedron shapes. The square box punch is therefore more adapted to preform the highly doubled curved shape with the case corner. [ABSTRACT FROM AUTHOR]