A simplified rate dependent model of forming and wrinkling of pre-impregnated woven composites

A simplified finite element model is developed and validated for the forming/draping of pre-impregnated woven composites, incorporating the effects of wrinkling and strain rate dependence. The model development builds upon previous work on simulation of fabric draping using a truss representation of the woven material. Tows are modelled by stiff elastic bar elements, and the non-linear rate dependent shear behaviour is incorporated in elastic-viscoplastic elements that follow an appropriate phenomenological constitutive model. Wrinkling due to tow buckling is simulated by allowing the deactivation of tow elements that undergo compressive deformation. The model convergence is tested and its validity is checked against experimental results from the forming of pre-impregnated woven carbon hemispheres. It is found that the model reproduces successfully experimental measurements of shear and wrinkling with a relative error of approximately 4%, while solution times are kept below 60 s on a conventional PC. These features allow potential iterative use of the model within a process optimisation scheme. The sensitivity of the process outcome to process parameters such as blank holder force and forming speed is investigated.