Izi-Direct – Innovative non-destructive method for inline characterization and quality assurance of discontinuous recycled carbon fiber semi-finished products

Increasing the sustainability of carbon fibers

High-frequency eddy-current measurement on carbon fibers is still a big research topic today. Our project coordinator Suragus is the only company so far which industrialized this technology. By enabling faster and easier quality testing of carbon fiber nonwovens, the project aims to lower the threshold for using products made from discontinuous (the carbon fibers in the nonwovens are cut fibers rather than continuous fibers), recycled carbon fibers, and increase acceptance of the material in the industry.

Eddy-current measurement for characterization and quality assurance of carbon fiber nonwovens made from recycled carbon fibers

For many years, science and industry have been dealing with the topic of recycling carbon fibers. Cut fibers and pyrolyzed end-of-life fibers can be processed as nonwovens into new components with good mechanical properties. To monitor these nonwovens' production better and enable subsequent non-destructive quality assurance, suitable eddy-current sensors for nonwoven and compound characterization must be developed and evaluated in the "Izi-Direct" project.

Here, the fiber orientation of nonwovens is determined via the electrical properties (instead of via image evaluation), i. e., sensors with specifically directed electromagnetic fields are positioned in a way that a direction vector for the dominant fiber direction can be measured from them.

Eddy current measuring device at Fraunhofer IGCV for the investigation of carbon fiber semi-finished products
© Fraunhofer IGCV
Eddy-current measuring device at Fraunhofer IGCV for the investigation of carbon fiber semi-finished products

The figure shows the measuring device from the company Suragus, which is used at Fraunhofer IGCV for eddy-current measurement.

A special sensor from Suragus allows the orientation of the carbon fibers in the nonwoven to be determined. This is a decisive parameter since the orientation of the fibers is decisive for the mechanical properties of the CFRP component produced from the nonwoven.

Example measurements for determining the fiber orientation
© Fraunhofer IGCV
Example measurements for determining the fiber orientation

Eddy current measurements were used to determine the orientation of the carbon fibers in UD material and isotropic carbon fiber nonwoven. The shown polar diagrams show results of example measurements.

An exemplary representation of the homogeneity of a nonwoven sample and the creation of calibration curves
© Fraunhofer IGCV
An exemplary representation of the homogeneity of a nonwoven sample and the creation of calibration curves

In addition to the orientation of the carbon fibers in the nonwoven, the homogeneity, basis weight, and fiber volume content of the nonwoven will also be monitored during production to increase the quality of nonwovens made from recycled carbon fibers. The eddy current sensors are evaluated and assessed through the research partners ITA Augsburg and Fraunhofer IGCV, both located at the Augsburg Technology Center and have strong contacts in the carbon fiber processing industry. The procedure of Fraunhofer IGCV is exemplarily shown in the following figure. On the one hand, the eddy current sensor can be used to evaluate the homogeneity of nonwoven pieces. On the other hand, a calibration curve can be determined from many nonwoven pieces, providing a basis for the inline application.

In addition to the sensor evaluation, the partner CIKONI is developing a simulation method for predicting the mechanical material properties based on the measured parameters and comparing them with the real behavior of carbon fiber plastics made from rCF nonwovens.

 

More interesting reference projects on this topic:

 

MAI Carbon »CaRinA«

»CaRinA« carbon fiber recycled materials for industrial applications.

 

MAI Scrap SeRO

From Scrap to Secondary Ressources – Highly Orientated Wet-Laid-Nonwovens from CFRP-Waste

 

WiPull

Standardization of the single fiber pull-out test to measure fiber-matrix adhesion.

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