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Organisationseinheit der BAM
The research presented here attempts to assess the potential for re-using carbon fibre (CF) fabrics recovered from recycling infusible acrylic thermoplastic carbon fibre reinforced polymer composites (CFRPs) in a universal manner, i.e. by combining with a wide variety of matrices to manufacture 2nd generation composite laminates by resin infusion. The 2nd generation composites have been compared in terms of bulk and interfacial properties against counteparts processed with virgin carbon fibre fabric infused with the same matrices. Generally, an increase in damping (tanδ) was observed in all 2nd generation composites, which can be attributed to a residual thin thermoplastic layer present on the recovered fibres. The interfacial adhesion of the 2nd generation Composites was investigated by shear tests and scanning electron micsoscopy, and also appears to be less influenced by the type of matrix.
In this work, a closed loop recycling process is investigated, which allows polymerised bulk thermoplastic matrix (Elium 150) from production waste (also referred to as recyclate) to be reused as additive in composite manufacturing by vacuum assisted resin infusion (VARI) of virgin Elium 150 monomer. It is shown that this process can save up to 7.5 wt% of virgin material usage in each processing cycle. At the same time, the thermal stability and stiffness of the composite increases with the proportion of recyclate introduced. Contemporarily, the shear and bending properties have also been observed to improve. Gel permeation chromatography (GPC) showed that the changes observed are due to an increase in molecular weight with the recyclate content. In particular, a correlation between the molecular weight and the shear properties of the composite was discovered using single fibre push-out tests.
In welding experiments conducted on heavy wall pipes, the penetration mode (full or partial penetration) occurred to be a significant factor influencing appearance of solidification cracks. To explain the observed phenomena and support further optimization of manufacturing processes, a computational model was developed, which used a sophisticated strategy to model the material. High stresses emerged in the models in regions which showed cracking during experiments. In partial penetration welding, they were caused by the prevention of weld shrinkage due to the cold and strong material below the joint. Another identified factor having an influence on high stress localization is bulging of the weld.
Laser GMA hybrid welds, producing partial penetration, were conducted on stiff tubes made of S460NH. Experiments, using a design-of-experiments plan were conducted to examine the influence of the welding parameters on the occurrence of solidification cracks. Results say that cracks diminish, when high levels of arc power are applied, while their number increases with rising laser beam power. The weld velocity had no measurable impact.