Multifunctional sensor yarns for real-time in situ detection of multiple damage mechanism for continuous structural integrity monitoring of components made of textile-reinforced composite materials

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The research project focuses on the development of a novel coaxial sensor yarn with only three functional layers, equipped with reproducible quality and defined homogeneous geometry, which is designed as a precise and continuously melt-spun core/sheath bicomponent monofilament structure. The core consists of the thermoplastic polymer PEEK, which is percolatively mixed with electrically conductive particles and completely enclosed by a bare PEEK sheath without additives. This high-temperature resistant high-performance polymer is suitable for direct integration into all technically relevant thermoplastic and thermoset matrix systems. Furthermore, the research aims the process development for the realization of defined parameterizable electrical reflection gratings in the form of periodically impressed cross-sectional gradients in the nickel layer deposited wet-chemically on the core-sheath structure and acting as an outer conductor. Additionally, the development of a fiber-based measuring method based on electrical time-domain reflectometry (E-TDR) will be investigated for the first time. The hereby related high spatial resolution for the investigation of different stages or geometric characteristics of the development and propagation of multiple structural damage mechanisms has to be investigated. This is premise for their reliable non-destructiv-measurement as well as for the precisely localizable or globally differentiable in-situ detection in components made of fiber-reinforced plastic composites. The innovative approach is based on the integral production of such sensor yarns as bicomponent core/sheath monofilament yarns with strictly homogeneous, re-producible and short-circuit-free construction by means of melt-spinning technology further developed to meet manifold requirements. Two novel approaches based on electrical time-domain reflectometry are being pursued for the production of a versatile yarn-based and machine-processable combination sensor that can be used for a variety of measurements. A robust contacting solution must be developed for both.It is based on the working hypothesis that the stresses initiated in the FKV by external superimposed loads lead directly to detectable structural events that change the microstructure and, depending on their severity, cause only local or global geometric changes in the sensory coaxial conductor struc-ture integrated over the dimension of the component to be monitored. This global or local geometric deformation of the coaxial sensor in the area of the geometric reflection points allows the measurement of the local change of the wave impedance, which allows in combination with a tailored to be developed evaluation strategy a precise, spatially resolved (re)-localization of struc-ture changes caused by structural degradations.