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FRP embedded micro-sensors on multifunctional substrates for curing process control

Subject Area Microsystems
Plastics Engineering
Lightweight Construction, Textile Technology
Term from 2017 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 397053684
 
Final Report Year 2024

Final Report Abstract

In order to save time, energy and costs in the production of fiber-reinforced plastics, as much information as possible is needed about what is happening during the manufacturing process. One of several ways of obtaining this information is to integrate film sensors into the manufactured components. These consist of a thermoplastic film on which metallic electrodes are structured. Integration into the component entails various advantages and disadvantages. On the one hand, component-integrated sensors can be used more flexibly than mold-integrated sensors and allow a higher spatial resolution of the curing processes. On the other hand, they become part of the product during production and should therefore be simple and inexpensive as well as not compromise load capacity. From a mechanical point of view, film sensors primarily pose a delamination risk. The decisive influencing factor is the choice of thermoplastic carrier material. Sensors based on the frequently used substrate material polyimide entail a considerable risk of delamination. The influence of polyetherimide, on the other hand, is far less damaging. Some tests show that polyetherimide-based sensors even improve individual strength properties. In addition to the carrier material, the metallic sensor structures also have an influence on the load capacity. For the design of minimally invasive sensors, the lowest possible degree of metallization should be aimed for. The most common design for foil sensors for cure monitoring are so-called interdigitated electrodes, which form an electrical capacitance whose impedance is influenced by the direct environment. In variothermal manufacturing processes, one challenge is to separate the influence of temperature from that of the degree of cure. The impedance information measured with integrated sensors must be processed to remove the frequency dependence and the influences of temperature and sensor geometry from the data. For this purpose, an algorithm was developed in the WG Sinapius based on extensive resin characterization, which calculates the degree of cure from measured impedance spectra and measured temperature data. The use of an additional temperature sensor is therefore indispensable for monitoring variothermic curing processes. For this purpose, WG Dietzel has developed an integrated multi-sensor node that measures the temperature information, the dielectric properties and additionally the strain state on a single film sensor. In addition to determining the degree of cure, the sensor data also offer potential for determining the fiber volume content or detecting resin mismatch.

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