Meso-scale model for the forming process of biaxial reinforced weft-knitted fabrics

Numerical modelling of textile materials is important for developing new forming processes of textile reinforcements for composite parts, namely to decide on forming tool geometry and forming process parameters such as blank holder forces. A numerical model reduces the application of trial-and-error, which significantly reduces costs and material resources. The magnitude and distribution of blank holder forces play a decisive role in the quality of the formed textile. In general, no or even low blank holder forces will lead to wrinkles in the useful part of the preform. This reduces the mechanical quality of composite parts reinforced by textiles. In contrast, excessive blank holder force will cause damage to the textile. To observe these effects in complex forming situations, a material model has to be found which takes all forming modes of textile materials into account. A meso-scale model for biaxial reinforced weft-knitted fabrics is introduced, in which present yarns are simplified and discretized by beam elements. A single yarn is considered as a chain of multiple beam elements. Methods of modelling the complex geometry of the reinforced knitted structure are presented. The models are suitable for virtual mechanical tests and large scale forming simulations.