Thermoforming of Knitted Composite Structures: FEM Simulation and Experiments

Specially designed knitted fabric reinforcements are proposed as a control mechanism for improving the thermoforming process for a broad class of thermoplastic composites. Benefits include improving the non-uniform thickness distribution on the final part and reducing undesirable sensitivity to changing thermal conditions. A hierarchical FEM in micro and macro scales is developed for the simulation of thermoforming with knitted fabrics and a practical example of stretch and thickness control is presented. Experimental validation is also given for uniaxial loaded knitted fabrics.