Modeling formability of multiaxial warp knitted fabrics on a hemisphere

The aim of this paper is to describe a model for the prediction of the formability of a multiaxial warp knitted (MWK) fabric to a 3D surface. For this purpose, we first characterized in detail the forming behavior of MWK fabrics containing two bias inserting yarns (TBMWK fabric). Through experimental observation, it was found that the two bias inserting yarns always tend to gather along the weft direction. The angle between the two bias yarns has a linear relationship with the perpendicular distance from the measured points to the longitudinal axis of the hemisphere during forming process. The slope of this linear relationship is also linear with the magnitude of radius of the pressing hemisphere provided that the radius is larger than 7 cm. Based on the above finding, a mathematical model is established for predicting the deformations of TBMWK fabrics during the hemisphere-forming process. The shape of flat TBMWK fabric that can yield the corresponding hemisphere during the forming process as well as local deformations can be calculated through this model. The hemisphere-forming experiments show that the present model is workable and accurate. The results from both the model and experiments suggest that the shape of flat TBMWK fabric that can yield the corresponding hemisphere which is close to a rectangular, not to a square as presented by woven fabric. The method developed in the paper has laid a foundation for further modeling of the forming behavior of MWK fabrics onto other 3D surfaces. More importantly, it is of great value to find that the two bias inserting yarns always tend to gather along the weft direction of the fabric which is a starting point for modeling of the forming behavior of MWK fabrics.