A methodology for characterization and assessment of carbon fibre non-crimp fabric textiles

Kurzfassung

Carbon fibre textile semi-finished products are playing an important role for the production of carbon fibre reinforced plastics via (liquid) resin infusion processes, e.g. in aircraft manufacturing and other industrial applications. The focus of the present work is on multiaxial warp knitted fabrics, also called non-crimp fabrics (NCF), a form of textile with the reinforcement fibres placed in multiple (mostly 2-4) layers upon each other, held together by a knitting yarn pattern. An assessment methodology is presented, comprising seven test methods, of which there are four on the processability of the NCF-textiles in part manufacturing and three to characterize the textile quality aspects related to laminate mechanical properties. For each of these test methods, approaches are explained to derive quantifiable values from the results to make the textile characteristics of different materials comparable. With regard to processability, the deformation or drape behaviour of the multiaxial fabrics and the alteration in textile quality by such processes are predominantly addressed. For this purpose, a test method for bulk and compaction characteristics is described as well as two test methods to characterize the in-plane (shear) deformation behaviour, one for biaxial and another for tri- and quadraxial warp-knitted fabrics. From the application of the test methods, results on the identification of the ply structure and textile production parameters governing this deformation behaviour are also presented. The area of processability is completed with a simple test on the infuseablity of the NCF with resin. For assessment of textile quality, methods to quantify the fibre angle deviations, both in and perpendicular to the textile plane are presented, as well as a method to assess the influences of the knitting yarn induced ply distortions. All tests can already be performed on the dry textile, before laminate specimen manufacturing and preparation. Concerning the laminate mechanical properties, examinations are made as to how the different structures of the dry textile are transferred into laminate structures. Furthermore, different approaches or theoretical models are applied to evaluate their influence on the compression strength of those laminates. The derived results are compared to real compression test data. The methods presented in this work enable to obtain a better comprehension of the correlations in NCF textiles and composites manufactured thereof. Thus, they allow a more structured and objective assessment of new NCF semi-finished products and the identification of weak points early in the selection process, to make a more precise and efficient material development possible. Furthermore, the methods can be used to ensure stable material properties in serial production, for instance during incoming / outgoing inspections.