The sales of carbon fibers will strongly increase due to the increasing demand of lightweight structures in the next years. 10 to 30 percent of valuable carbon fiber waste is produced by blending, of-spec material and end-of-life parts in aerospace. End of Life vehicle guideline which includes that 85 percent in a car has to be recyclable and a land fill ban in Europe puts the carbon fiber sector under much pressure. Therefore research is focused on recycling. There are three main types: material, thermal and chemical recycling. Since every component has to be shredded before recycling carbon fibers lose their length and woven structure. These fibers can only be reasonably be reused in a mat. Carbon fiber mats can be produced by using air-lay processes, carding machines and wet-lay processes. For investigations at University of Applied Sciences Niederrhein the wet-lay process has some advantages such as absence of conductive dust which can damage electrical appliances.
Main objective of the project is the feasibility of wet-lay process with recycled carbon fibers and further processing to composites with Resin Transfer Molding process. After that the composites are analyzed concerning their orientation and mechanical properties to fix possible applications. Emphasis is put on strength, elastic modulus, flexural stiffness and energy absorption for creating a data sheet for this composite. Included is the investigation of different parameters as fiber length, fiber volume fraction, dispersing agents, bonding agents and different resin systems. Sub-sequently, G’sell Jonas equation is used to model dependency of temperature and strain rate. Helius Composite 2017 and ANSYS Workbench 18.2 are used to simulate the mechanical properties with reasonable agreement to the measured values.
One result is the successful manufacturing of carbon fiber fleece in industrial scale. Main findings is, that pyrolysis fibers with hydroxyl ethyl cellulose and Polysobat 85 reach the best results. Generally fleece with an areal weight of 30–100 g/m² and a maximum fiber length of 12 mm can be produced. For impregnation a maximum fiber volume fraction of 50% can be realized in the composite. Some of the investigated parameters showed no effect on the mechanical properties. These parameters are fiber areal weight, types of dispersing agents and different resin systems. Other parameters as fiber volume fraction, fiber length and bonding agents have positive effects while amount of dispersing agent has negative effects. In consideration of characterization the simulation of deformation with uniaxial and multiaxial loads was carried out. Therefore ten unidirectional layers with different orientations are needed to model the isotropic fleece composites in the software. As a result a high accuracy of 16.17% could be achieved.
|Advisor:||Gutmann , Jochen|
|School:||Universitaet Duisburg-Essen (Germany)|
|Source:||DAI-C 81/2(E), Dissertation Abstracts International|
|Subjects:||Materials science, Chemistry|
|Keywords:||Fiber-reinforced thermosets, Fleece, Carbon fiber recyclate|
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