Key Engineering Materials Vol. 742

Abstract: Injection moulding of thermoplastic melts is based on the source flow. This principle allows for the production of mouldings in skin-core structure: the core enclosed on all sides by skin material may consist of a different or modified thermoplastic material. Generally, this method is referred to as co-injection or also sandwich injection moulding.Known applications of this method include processing of recycled material in the core and new material for the surfaces, foaming (chemically and physically) of the core material, processing of filled core material, e.g. Glass fibres and unfilled material for the surfaces. Other combined methods, e.g. with gas and water injection, are possible.The report describes the nozzles and hot runners developed by A&E Produktionstechnik Co. for the application of this method. Sample mouldings, produced and developed by customers and research cooperation partners, demonstrate the potentials and limits of the procedure in regard to the combination of different thermoplastic melts in a moulded part.

Abstract: Multi-material solutions offer numerous benefits producing tailored-made hybrid components with enhanced application-optimized properties contrary to conventional monolithic parts. However, designing of corresponding manufacturing processes is often challenging due to various technical aspects. This paper represents a process route for the manufacturing of a hybrid bevel gear by means of tailored forming technology with a focus on die forging and describes the main challenges within the forming stage. Due to local material-specific properties, uncommon material flow and complex geometry of the final part, an individual forming tool system with a geared die was accurately designed. Besides the forming tool system, the FE-based design of the forging process as well as the necessary material characterisation will be presented. Finally, the initial results of the experimental forging investigations are shown.

Abstract: For the development of an efficient and economic recycling process of carbon fibers (CF) still many technological challenges have to be mastered. One of them is the removal of all extraneous natural and synthetic fibres, e.g. polyester sewing threads. The objective of the research was to develop an in-line process for the removal of those extraneous fibres, which result from mechanical processes such as tearing. A promising approach for the removal of extraneous fibres from cut-off carbon-fibre material (CF) has been identified, getting recycled carbon fibres (rCF). For that purpose, the use of modern laser technologies is particularly promising. However, the focus was not the development of new laser systems, but the adaptation of existing technologies and their integration into textile processing steps for carbon fibre recycling. In addition to the removal of the extraneous fibres, the degree of CF losses and quality degradation due to fibre damage have been analysed and compared with optimum fibre characteristics. The separation has been experimented and corresponding laser parameters have been defined. Finally, the obtained carbon-fibre material has been tested with regard to its processability in textile manufacturing processes (dry non-woven fabric production) up to carbon fibre reinforced plastics (CFRP). For the evaluation of the material for potential applications, test plates from irradiated and non-irradiated material have been used. The performed tensile and flexural tests have proved that the irradiated material has similar properties compared to the non-exposed one.

Abstract: In this study different materials made out of cut-off as well as reclained carbon fibres (rCF) are described and compared. For this benchmark nonwovens, compounds, SMC, BMC, as well as standard lightweight materials like high alloy steels, aluminium and magnesium are taken into account. Specific mechanical properties like modulus and tensile strength are used to show the lightweight potential of recycled carbon fibre materials in ashby charts. It is shown that rCF products can substitute glass fibre applications and are also comparable to metals and alloys.

Abstract: The main objective for an economic and ecological use of raw materials is the achievement of closed raw material cycles. Because of that, not only the manufacturing procedures are important during the development of new materials but also the recycling processes. Within the increased use of lightweight construction in recent years, the application of multi-material or hybrid structures reach high significance for the automotive industry. In this development, especially the carbon fibre reinforced plastics (CFRP) gained its importance. However, currently there are no recycling strategies available for hybrid structures; complete recycling processes for CFRP are still expandable. This work presents methods for separation of hybrid structures made of metal and CFRP, as well as the corresponding process windows and the boundary conditions. The separation is performed by introduction of thermal heat and the behaviour of these bonded compounds is analyzed based on shear tensile tests. The results of these studies are used to develop a complete recycling process for reclamation of hybrid structures.

Abstract: In this study, sized and thermally desized virgin carbon fibers (vCF) as well as recycled carbon fibers (rCF) from a thermal recycling process are plasma treated by a plasma-jet. The effect of two different process gases (nitrogen and dinitrogen monoxide) and the influence of the distance between the plasma source and the fiber surface are studied with the aim of increasing the oxygen and nitrogen concentration on the rCF surfaces. Higher surface coverage of oxygen-and nitrogen-containing functional groups is supposed to lead to a better adhesion between the carbon fiber and the epoxy resin matrix. The elemental compositions and functional groups of the treated carbon fiber surfaces are studied by x-ray photoelectron spectroscopy. The effect of plasma treatment on the fiber properties like tensile strength, tensile modulus and surface roughness is investigated.

Abstract: The increasing demand for composites leads to a growing amount of end-of-life materialand production waste. The latter consists of a large fraction of unimpregnated fibre waste which is notsufficiently reprocessed using conventional textile processing procedures as they are either too expensiveor their mechanical performance is too low. Using pieces of dry non-crimp fabrics (patches) ina Bulk Moulding Compound process (BMC) displays a straightforward approach of fabric recycling.Adding fillers to the mixture not only offers the opportunity to modify mechanical and electrical propertiesas well as the costs but also a chance for a more holistic approach of dry fibre recycling, whenconventional fillers like chalk are replaced by ground recycled carbon fibres. In this way, all kindof dry fibre wastes can be reused in one process: Larger offcuts are chopped to smaller rectangularpatches whereas waste fractions of small offcuts are processed to carbon fibre powder as filler andprocessed together with resin to produce BMC materials. Mechanical investigations reveal that thepresented approach shows higher specific properties than the conventional filler without compromisingthe process and material quality.

Abstract: The purpose of this paper is to evaluate the eco-efficiency of three different recycling technologies for carbon fiber reinforced plastic (CFRP) waste, and to identify the preferable and most efficient solution. Recycling via mechanical shredding, microwave pyrolysis and subcritical solvolysis is compared and comprehensive primary data on energy demand and process throughput are examined. Following an ecological and economic assessment, the results are normalized and summarized into three single-score indicators. To decide which solution is most efficient, economic and ecological data are plotted on an eco-efficiency portfolio. The achieved results demonstrate that the eco-efficiency of the recycling technologies investigated is entirely positive on an industrial scale, and that the efficient use of CFRPs across the entire life cycle is possible. The material recycling of CFRP waste is consequently a promising topic for future development. The use of recycled material as conductivity additives in secondary applications can be considered as a valuable option for all three technologies, although the benefits of recycling are strongly dependent on the quality and quantity of the recycled material. Depending on the resources substituted in a secondary application, different recycling technologies offer considerable advantages. To ensure a consistently high quality of output materials on an industrial scale, specific process parameters have to be identified, for which, further research is necessary.

Abstract: In order to sustainably establish carbon fiber reinforced polymer composites (CFRPC) in the market on an industry scale, solutions on how to recycle these new materials have to be developed. Quasi-continuously aligned carbon staple fiber structures in organic sheets made of recycled carbon are one approach which will be dealt with in this article. The process chain as well as the mechanical properties will be presented. Moreover, the specific feature of staple fiber yarns to be able to plastically deform under process temperature, enabling new degrees of deep-drawing of CFRPC organic sheets in the thermoforming process, will be highlighted.

Abstract: Through the combination of two or more materials to one compound, for example high-strength steel and aluminum, hybrid massive components can be manufactured, whose properties are specially adapted to the respective application. One of the challenges is the joining zone which is influenced by machining induced residual stresses. In order to examine the residual stress modifications by the machining process and in addition to analyze the influence of these residual stress gradients on the lifespan of hybrid components a non-destructive method of measuring depth-resolved residual stress is necessary. Therefore, an innovative energy dispersive X-ray measurement technique is used in the collaborative research center 1153 (CRC 1153). In this study the suitability of the method is examined by comparing the results with the angle dispersive method both in machined front surface of mono materials and hybrid shafts. A parametrical study shows the possibility to get greater depth information by variation of the measuring parameters Bragg angle, tilting angle, collimator and current. In addition, the results of the energy dispersive method combined with electrolytic removal is shown. Based on these results the evaluation of the reliability and reproducibility of energy dispersive residual stress measurements is completed.