Numerical and experimental investigation of manufacturing and performance of metal inserts embedded in CFRP

Due to their outstanding specific mechanical properties, carbon fibre reinforced plastics (CFRP) exhibit a high application potential for lightweight structures. With respect to multi-material design and to avoid drilling of structural CFRP parts to join them to other components, embedded metal elements, so called inserts, can be used. The inserts consist of a shaft and a baseplate which is embedded between the fibre layers. So far, only punctiform inserts have been subject to research. One feasible geometry are linear inserts which have not been studied yet. In this work, the performance of two different types of linear inserts will be investigated. The shapes are based on a punctiform insert which is made out of a threaded shaft welded onto a baseplate whose performance under different types of loading has been investigated before. The first type of linear inserts has the same cross-section as the reference punctiform insert but is of a linear form. The second type is a quasi-linear insert which consists of a baseplate with the same dimensions as the first linear inserts and three threaded shafts welded onto it. All samples are manufactured by resin transfer moulding (RTM). Depending on the geometry of the insert and the preforming concept it is potentially possible to maintain the fibre continuity. For the inserts with a continuous shaft and in the proximity of the insert, it is necessary to cut fibres of the top layers which are aligned perpendicular to the shaft. For the quasi-linear insert, it is possible to maintain the fibre continuity as the fibres are guided around the circular shafts. Additional to mechanical tests that are carried out, mould-filling and curing simulations are performed for different inserts to analyse the influence of the process parameters onto the part quality. In the main series of tests, the specimens are characterized regarding their failure behaviour and load bearing capacity under quasi-static loads. The results of the experiments show that, compared to the punctiform reference insert, the linear load introduction elements exhibit higher load bearing capacity. However, the linear load introduction elements are inferior regarding specific load bearing capacity and furthermore increase process complexity during preforming and production.