Stress analysis and design suggestions for multi-loop carbon roving rosettes to reinforce bolt-loaded open-hole laminates

Abstract

The potential of mechanical joints in monolithic carbon fiber reinforced plastics (CFRP) laminates is limited by the poor local bearing response under bolt loads. To improve the mechanical performance of bolt-loaded open holes, often metallic inserts or fiber reinforcements like Advanced and Tailored Fiber Placement (AFP, TFP) are used. In this work, an alternative to AFP and TFP is investigated, where winded carbon rovings are twisted around the bolt and work without sewing. These multi-loop rovings consist of turns around the hole and free slings in the design area around the hole. Based on previously conducted experimental and numerical studies, published in Botzkowski et al. (2016), a model generator has been developed to build up three-dimensional finite element (FE) models on mesoscopic level. The model generator is capable of considering variable design parameters of the multi-loop rosette as well as manufacturing effects like changes in cross sections of the rovings. The applied material models have been parametrized by experimental tests at single-loops and non-reinforced reference laminates. By applying the model generator, various multi-Loop configurations with varying number of turns, number of loops, loop orientations and loop lengths are generated and evaluated in terms of their stress behavior and load bearing capacity. Finally, design proposals for winded multi-loop roving rosettes are derived.