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Simplified Analytical Stitch Model for Non-Crimp Fabrics



Non-crimp fabrics (NCFs) have become increasingly popular for cost effective applications of composite parts. Two dimensional NCFs are draped into three dimensional geometries in the preforming process and consolidated with resin via injection. The drape quality after forming is evaluated by the occurrence of unwanted drape effects like in-plane undulations, gaps and fisheyes and out of plane loops and folds. NCFs consist of unidirectional reinforcement tows that are fixed with a throughthickness stitching yarn. The drape effects undulation and loop occur in NCFs when the stitching yarn is strained during shearing. The strained stitching yarn prevents further rotation of the tows and the tows start to buckle. A simplified analytical stitch model based on the stitching yarn strain during shearing was developed to describe the relationship between the manufacturing parameters, the shearing process parameter and the drape behavior of NCFs. The occurrence of the drape effects gap and fisheye depends only on the manufacturing parameters. The gap-fisheye-index was developed to describe the formation of gaps and fisheyes in NCFs. NCFs with selected manufacturing parameters were produced and the developed models were correlated to experimental results.

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