Experimental and numerical studies on the braiding of carbon fibres over structured end-fittings for the design and manufacture of high performance hybrid shafts

Abstract

Braiding is an attractive manufacturing method for tubular elements such as hollow shafts and struts. One of the main challenges however is the integration of suitably performing end-fittings. Recent advances in additive layer manufacture have enabled the fabrication of end-fittings which can be 'co-impregnated' or 'co-cured' with the fibre preform in a single step, i.e. without the need for secondary adhesive bonding. This requires the introduction of protrusions onto the surface of the end-fitting to promote mechanical interlocking with the fibres. However, the lack of accurate modelling tools for the simulation of this manufacturing process means that much empiricism is currently used in the design of such structures. A novel numerical framework is presented here for the full-scale simulation of the braiding process over structured end-fittings. Nonlinear finite element analysis is applied at the meso-scale, with strands of beam elements representing individual yarns and meshed surfaces modelling the mandrel and tooling. Penalty-based contact formulations are then used to simulate all inter-yarn and yarn-metal interactions, enabling detailed predictions of fibre paths around surface protrusions. In order to verify and validate this numerical framework, a series of full-scale braiding experiments was conducted using additivelymanufactured thermoplastic mandrels. Final braid patterns as well as the occurrence of braid imperfections were investigated and compared to model predictions. It is shown that the proposed modelling strategy reproduces well the trends observed experimentally in terms of final braid quality. A parametric study was then conducted on the effects of initial end-fitting alignment with respect to oncoming yarns, suggesting that better control over this parameter could reduce considerably the occurrence of braid imperfections.

Mechanical analytical modelling of non-axisymmetric overbraiding

“…Finite element mechanical modelling of the braiding process has been shown to generate satisfying braid angles on complex mandrel shapes. [8][9][10][11] However, an industrial use of such techniques remains difficult due to the very long calculation times, in the range of several hours to days depending on the number of yarns and the length of the mandrel. 10,11 For these reasons, the FE method does not appear as a promising solution to allow a fast process optimization.…”

“…[8][9][10][11] However, an industrial use of such techniques remains difficult due to the very long calculation times, in the range of several hours to days depending on the number of yarns and the length of the mandrel. 10,11 For these reasons, the FE method does not appear as a promising solution to allow a fast process optimization. In this context, the mechanically enhanced kinematic approach could be an interesting method to allow a fast and accurate modelling of the braiding process if it could be extended to nonaxisymmetric braiding conditions.…”

“…It would therefore exhibit novelties compared to the axisymmetric analytical interaction model presented by van Ravenhorst and Akkerman 7 as well as calculation time reduction compared to the recent FEM simulations. 11 In the frame of this work, the implemented physical phenomena are yarn undulation and frictional yarn-yarn interactions. Nevertheless, the presented model could serve as basis for the implementation of further physics, as evolution of the yarns cross sections or yarn-yarn lateral interactions in jamming conditions.…”

“…Braiding pattern. Yarn undulation due to the interlacements of the yarns is implemented in the description of the braid equilibrium in equation (11). In Sun et al, 11 recent FEM simulation techniques have been used to simulate the braiding of 450 mm long cylinders with 36 yarns and a braid angle of 45 .…”

“…Yarn undulation due to the interlacements of the yarns is implemented in the description of the braid equilibrium in equation (11). In Sun et al, 11 recent FEM simulation techniques have been used to simulate the braiding of 450 mm long cylinders with 36 yarns and a braid angle of 45 . Simulation parameters, listed in Table 3, are used in order to generate the same braid characteristics as in Sun et al 11 with two different braiding patterns.…”