Colloquia

Summary

Continuous fibre reinforced thermoplastic composites (TPCs) are increasingly used in industries such as aerospace and automotive, because they combine high specific properties with a capability for high-rate manufacturing. One of the most used production techniques for TPCs is hot press forming. To date, the process is mostly limited to rather simple geometries and woven fabric reinforced composites. Application of the hot press forming for more complex components from unidirectional (UD) reinforced composites is difficult because unwanted defects, such as wrinkles, may form during the process. Process optimisation to prevent these defects are based on trial-and-error and can be time-consuming and expensive. Therefore, engineers make use of predictive simulation software that allow virtual process optimisation.

Press forming simulations are based on deformation mechanisms of the composite material, one of which is intra-ply shear. Previous studies have found a relationship between the formation of wrinkles and (the inhibition of) intra-ply shear. This brings us to the goal of this study, which is to use UD cross-ply thermoplastic composite forming experiments to provide validation cases for the intra-ply shear deformation predicted by these simulations. To achieve this, a method was developed to quantify the deformation of the press-formed composites. The method is based on the photogrammetry, which can digitise a deformation patterns to a pointcloud, from which then the intra-ply shear can be calculated. The method is applicable to a wide variety of configurations. The accuracy of the method mainly depends on the resolution of the pattern and the quality of the photo’s. These combined are applied in a worst case scenario as a measure for the accuracy. The comparison with the forming experiments and the corresponding simulations has been done by mapping the results using a projection algorithm.

Six different configurations for forming experiments were chosen for validation. Comparing the simulations with the experiments, it is concluded that the simulations seem to predict the forming process quite well in general, although the material model of the simulations allows for more shear than in reality occurs. Additionally, it can be seen that there is a relation between the location of shear in the flat regions and the length of the wrinkles. In these critical areas, the accuracy of the quantifying method is the highest and do not seem to have significant impact on the results. As a consequence, it can be concluded that the predictive quality of the simulations could be improved by further studies to the characterisation of intra-ply shear.