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Over the past few years were developed some manufacturing processes involving resin impregnation in dry preforms prior to cure, and more specifically resin infusion across the fabric thickness in the so-called Resin Infusion Processes. Therefore, in these growingly used processes the transverse permeability of the fabrics will control both manufacturing cycles and dimensions, and consequently the mechanical properties of the final composites. A big effort has been realized to obtain reliable experimental techniques for measuring the transverse permeability. Since the differentiation between saturated and effective permeabilities is still discussed, and the flow front is hardly defined in such small dimensions (order of 1 mm), our measurements on some so-called Non-Crimped New Concept (N C2) are carried out for saturated flow, i.e. the fiber network is completely impregnated from the onset of the experiment. In our case [1], these measures rely on the measurements of the pressure drop induced by the flow of a controlled fluid across the fabrics, easily converted into transverse permeability through the Darcy's law. One of the main results of these measurements is that the low N C2 transverse permeability depends on the face of the fabric receiving the fluid. This original behaviour may, in turn, be translated into manufacturing guidelines to achieve optimal processing configuration. An attempt to relate this differential to the stitching hole surface is proposed which turns to explain minor phenomena. On the contrary, the 3D shape of the stitching hole reconstruction from polishings could yield some proper explanations.

Abstract. This article presents a first approach of hygrothermal microcracking in stitched crossply laminates. The presentation includes the definition of the material mesostructure and the selection of a characterization method adapted to the specificity of the study. The hygrothermal loading selected is discussed and the evolution of the crack density in stitched crossply composites during the loading is presented and commented.

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