This conference paper was submitted for presentation at the NAFEMS World Congress 2025, held in Salzburg, Austria from May 19–22, 2025.

Abstract

The usage of carbon-fibre reinforced composites (CFRP) to achieve lightweight structures has further spread throughout the last years in machinery and aerospace industry. The lifetime prediction and structural health monitoring (SHM) of these structures is necessary and costly. The usage of magnetic microwires embedded within the CFRP is aimed to enable wireless SHM of the components in service. In our setup, cobalt-rich magnetic microwires covered by a glass coating are used within noncrimp fibre (NCF) composites. These magnetic microwires change their electromagnetic properties while being thermally and/or mechanically loaded. This change can be detected and measured wirelessly using a handheld reader system. To achieve a robust signal, electromagnetic simulations are carried out in parallel to experimental work to understand the physical basics of the interaction between CFRP and the metallic microwires regarding electromagnetic fields. Unidirectional CFRP shows high orthotropy regarding electromagnetic properties. Industrially far more relevant multi-ply multi-directional carbon composites exhibit a quasiisotropic electromagnetic behaviour, which is favourable to the accuracy of the measurements. To achieve a good signal a frequency range from MHz to GHz is investigated for evaluating the best signal to noise ration. A comparison of the attenuation at 50 MHz and 2.45 GHz shows good correlation between simulations and measurements. The signal strength difference is 10^3 (!) To check for practical industrial usability, mechanical simulations (FEM) are performed to ensure that the measuring range covers the generally used allowable strains of up to 0.4%. While accounting for the thermal mismatch in the production process, the orthotropic mechanical material properties of multi-ply CFRP and microwires as well as the rupture strains of the microwires, the simulations show that measuring ranges of up to 1.5% are to be expected. Simulating different failure scenarios like delamination, cracks, dents or penetration were carried out to differentiate the signal resulting from different failure scenarios and sizes. The results indicate that metallic microwires can be used for SHM. Additional work will be carried out to achieve an advanced differentiation of the different failure scenarios. The portable reader will be redesigned to achieve more robust signals and to allow a quantitative signal assessment regarding different failure modes of CFRP. The work is carried out within the Horizon Europe framework (HORIZON-CL5-2021-D5-01) 'œINFINITE - Aerospace Composites digitally sensorised from manufacturing to end-of-life'