Solid-shell element for modeling consolidation-induced wrinkle defect formation

When consolidating thick fiber-reinforced composite laminates through compaction, the reduction in thickness may cause wrinkle defects to form. These defects considerably reduce the structural properties of components. The lack of robustness of this manufacturing process is one of the reasons why, in the aerospace industry, composite structures are designed using large safety factors. A numerical method to predict these defects was proposed in the literature [1], wherein a ply is modeled as having a homogeneous constitutive response. Multiple plies and the resin rich regions between them are then homogenized through kinematic enrichment. The authors observed that an overly coarse mesh in the through-thickness direction did not converge. In this work, their method is combined with a solid-shell element formulation [2] to allow the use of a single element through the thickness, aiming to increase the speed of the simulations. The initial approach makes use of an implicit finite element solver. This works well for compaction, as the timescale involved is typically in the order of hours. However, it is impractical for forming, as this process occurs in second(s). Meanwhile, the aerospace industry is striving for higher throughput, which could be enabled by multi-ply forming. This scheme could aid in finding adequate deposition conditions. For this reason, as well as to further reduce the computational cost of simulations, the element and constitutive behavior were implemented in the explicit in-house finite element solver SimTex with three alterations. The adaptive hourglassing-stabilization stiffness was altered to work with the anisotropic material, an iterative step was removed from the kinematic enrichment scheme, and the compaction limit was modelled as an elastic- rather than viscous phenomenon to bound the apparent stiffness. Although the predictive capabilities of the resulting scheme are limited by its dependence on the timestep, wrinkling can be predicted correctly with the solid-shell element.