Introduction
Microwave (MW) heating at an industrial scale is becoming increasingly popular due to the advantages of volumetric heating. However, the limited understanding of the coupling of electromagnetic fields with heat transfer mechanisms during production processes has restricted the use of MW heating at high scales. Simulation of this phenomenon can increase the confidence of the MW process. An accurate simulation requires precise material properties. One such significant material property is the dielectric permittivity (DP).
DP is material, temperature and frequency dependant and, in anisotropic materials such as composites, it is orientation dependant as well. There are no systems available in the market which fulfil these requirements and can accommodate solids (including composites) and liquids in the same system. Simulation of MW processing of composites requires measurement of DP at MW frequency (2.45GHz) and at different temperatures throughout the processing window for multi-layered materials and liquid resins. TWI is developing a dielectric measurement system through the EU-funded SIMUTOOL project, which accommodates all the above requirements.
Project background
The SIMUTOOL project was launched by TWI Ltd (co-ordinator), Loiretech SAS, Ecole Central De Nantes, Engineering Technology Solutions EE, ESI Group, OTTO-Friedrich-Universitaet Bamberg, Faurecia Automotive Composites and Airbus Group SAS in September 2015. It develops a simulation platform for the manufacturing of composites through MW heating. The simulation includes the electromagnetic field coupled with heat transfer mechanisms that take place during the production process. It will also include the process control loop, which will enable the optimum design of the manufacturing process. One of the major outputs of the simulation platform is the successful design of a ceramic matrix composite tool with a MW absorbing layer in order to maximise the energy-saving potential of the MW heating process. The other main output of the project is the dielectric measuring system.
Technical development
The MW frequency dielectric measurement strategy of the SIMUTOOL project is based on the adoption of a non-resonant, transmission-reflection waveguide-based, two-phase approach. Measurements can be made through out the heat cycle of a material and the system can go up to 400⁰C supporting both thermoset and thermoplastics. It can accommodate both solid and liquid specimens. Measurements can be made on specimens with a cross-section up to 50mm in diameter. The cross-section can be either circular or rectangular. As the cross section of the specimen can be high, the system is suitable for isotropic materials such as composites, which can have multiple layers with different fibre orientation.
Acknowledgement
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 680569.
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http://www.simutool.com/