Characterization and analysis of wrinkling behavior of glass warp knitted non-crimp fabrics based on double-dome draping geometry

Abstract

The good formability of textile composite materials over complex mold geometries is one of the reasons to make their use expanding in various modern industries. However, different defects in these reinforcements could have occurred during the forming step in the manufacturing process. The defects are arising for many reasons; some are related to the fabric itself and others related to the draping parameters. Understanding the textile structure mechanics and draping behavior is essential to choose the proper reinforcement as well as to attain better simulation. Fabric wrinkles and local out-of-plane bucking of yarns were the fundamental defects in focus. The main objective of this part of the project was to experimentally investigate and compare the draping behavior of six commercially available glass fabrics from the same category of warp-knitted non-crimp fabrics (WKNCFs). The tested fabrics included two stitching patterns: tricot and chain. Also, they were relatively heavy with approximate mass per square meter. A double-dome punching test was performed to implement draping for each fabric; then, the defects were detected and characterized. Punching load-displacement curves were also recorded. In addition, a defect code was designated for the main defects to characterize forming defects at the meso-macroscopic scale. The structure and the number of fabric axes, stacking sequence, and stitching pattern all contribute to defect formation during draping. The studied configurations in this paper can help in studying the simulation of deformed technical fabric and provide a method to minimize and even eliminate the draping defects.

Advances in composite forming through 25 years of ESAFORM

“…This work also includes specific problems as fabric-tool friction characterization [93], localization of transverse tension [86], superposition of transverse tension and shear [94], difficulties in assessing the strain fields via DIC, caused by the fabric surface distortion [95], compaction characterization [96], forming of NCF composites with continuous NCFs [97]. The special attention is on wrinkling and other local defects of draping [98][99][100][101] and its predictability during forming on part level [102]. Deformability of thermoplastic NCF sheets was studied in nearprocessing conditions in temperature and strain rate [103].…”

Material characterisation of biaxial glass-fibre non-crimp fabrics as a function of ply orientation, stitch pattern, stitch length and stitch tension

“…This geometry has already been used in multiple studies. 7,11,13,[29][30][31] The measured variables are the shear angle distribution and strains resulting from the draping process. Additionally, the occurring draping defects are recorded by means of an optical evaluation.…”

“…The shear and drape behaviour of unidirectional NCF has been characterised in Schirmaier et al 12 by bias extension and picture frame tests. Draping experiments with a double-dome geometry were conducted in Ali et al 13 for unidirectional, bi-, tri- and quadaxial NCFs. The defect evolution (e.g.…”

Experimental testing method to characterise the drapability of UD non-crimp fabrics used in wind turbine blades

“…To characterise the shear deformation behaviour of fabrics, picture frame tests [5,6] and uniaxial bias extension tests [7,8] are commonly used. Several researchers have worked to characterise and analyse of wrinkling behaviour of fabrics with hemispherical [9], square box [10] and double-dome [11] punching preforming methods.…”