Micro-leveled modeling of structural stitched FRP joints as energy absorbing rupture points

Compared to their capability for compression loads, continuous fiber reinforced polymers show poor energy absorption capability for tensile or bending loads. An appropriate structural design must compensate this disadvantage. Following an integrated lightweight strategy, connecting elements can be addressed as energy absorbing points. Consequently, textile seams between FRP components can be used. Adapting the stitching layout allows the failure process to be adjusted. However, appropriate design principles have to be identified in order to optimize the energy absorption. For this purpose, a parametrized finite element model of a single lockstitch was developed based on real stitching geometries and validated with experimental data. The validated numerical analysis helps in evaluating the influence of the thread properties and the stitching design. The parameter study reveals a strong influence of the thread material. In a loaded seam, polyamide yarns with a distinctive plasticity offer much better energy absorption capacity than high tenacity UHMWPE (Dyneema) threads. Furthermore, friction between the yarn and the surrounding material as well as wide stitch lengths are beneficial for energy absorption.