High-resolution eddy current sensor system for quality assessment of carbon fiber materials

Abstract

Carbon fiber materials become more and more important for many applications. Unlike metal the technological parameters and certificated quality control mechanisms for raw carbon fiber materials (RCF) have not been developed yet. There is no efficient and reliable testing system for an inline inspection and a consecutive manual inspection of the RCF and the post laminated carbon fiber reinforced plastics (CFRP). Based upon the multi-frequency eddy current device developed at Fraunhofer IZFP structural and hidden defects such as missing carbon fiber bundles, lanes, suspensions, fringes, missing sewing threads and angle errors can be detected. Due to the help of an optimized sensor array and an intelligent image pre-processing algorithm the complex impedance signal can be allocated to different carbon fiber layers. This technique enables the detection of defects in the depth up to five layers including the option of free scale measuring resolution and testing frequency. Appropriate parameter lists for an optimal error classification are available. The dimensions of the smallest detectable defects are in the range of a few millimeters. A prototype of a special single sensor and an eddy-current sensor array have been successfully developed thus the way to transfer the prototype into an industrial application is open.