Experimental characterization of holding force thresholds for dry glass fabric preforming

Precise control of gripping forces is essential for automated preforming of technical textiles to prevent material damage while ensuring reliable handling. This study investigates the holding force thresholds causing shear deformation in four glass fiber-based fabrics: one woven fabric and three non-crimp fabrics (NCFs). A novel experimental setup combining a universal testing machine, a coanda gripper, and a laser profile scanner was used to detect the onset of relative motion and determine the critical holding forces. Preforming tests with two coanda grippers evaluated the maximum forming height using two different pressure configurations. The results demonstrate a linear relationship between applied pressure and holding force, with critical forces inversely correlated to air permeability. The analysis shows that friction properties and flexural stiffness are critical factors for bond reliability, with flexural stiffness exhibiting a strong negative correlation (HR = 0.013) with the risk of failure. The regression analysis also shows that optimal alignment is crucial. These results underscore that strategic material selection and optimal fiber alignment can positively influence the forming height.