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D. Colaianni
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Electrical Characterisation of Unidirectional Thermoplastic Composite Tapes
Influence of Microstructure and Manufacturing Route
The increasing use of thermoplastic composites (TPC) in aerospace structures calls for a better understanding of their functional properties, particularly for unidirectional (UD) tapes. These materials offer advantages in automated manufacturing and weldability, but their electrical behaviour is inherently complex due to strong anisotropy and microstructural variability. This study therefore investigates the relationship between manufacturing route, microstructure, and electrical conductivity of UD TPC tapes, with an outlook on their applicability in the induction welding process.
A multi-method experimental approach was adopted, combining six-probe electrical measurements, infrared thermography, eddy current testing, and optical microscopy. Four different UD TPC tape systems, produced via distinct manufacturing routes, were characterised and compared. The results demonstrate that electrical conductivity is primarily governed by fibre volume fraction, but is significantly influenced by microstructural features such as fibre distribution, polymer-rich regions, defects, and thickness variations. Deviations from idealised models, such as the Rule of Mixtures, highlight the importance of local fibre connectivity and interfacial effects in determining conductive behaviour. Infrared thermography and eddy current testing revealed that electric current pathways are highly dependent on both internal architecture and surface condition, with polymer-rich layers limiting current injection and promoting localised conduction. Microstructural analysis confirmed that manufacturing routes directly influence fibre arrangement and polymer distribution, resulting in distinct electrical responses across the investigated materials.
This study also identified limitations in conventional conductivity measurements, particularly related to geometric assumptions and thickness variability, and proposed a normalisation approach to reduce associated uncertainties. Furthermore, finite element modelling of inductive heating demonstrated that the strong anisotropy of UD TPC tapes limits the formation of effective eddy currents, leading to poor heat generation compared with more isotropic laminate configurations.
Overall, this work establishes a direct link between manufacturing, microstructure, and electrical behaviour in UD TPC tapes. The findings provide valuable insights for improving material characterisation, enhancing modelling accuracy, and enabling practical applications such as in-situ quality control during tape manufacturing and optimisation of induction-based processing techniques.
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A multi-method experimental approach was adopted, combining six-probe electrical measurements, infrared thermography, eddy current testing, and optical microscopy. Four different UD TPC tape systems, produced via distinct manufacturing routes, were characterised and compared. The results demonstrate that electrical conductivity is primarily governed by fibre volume fraction, but is significantly influenced by microstructural features such as fibre distribution, polymer-rich regions, defects, and thickness variations. Deviations from idealised models, such as the Rule of Mixtures, highlight the importance of local fibre connectivity and interfacial effects in determining conductive behaviour. Infrared thermography and eddy current testing revealed that electric current pathways are highly dependent on both internal architecture and surface condition, with polymer-rich layers limiting current injection and promoting localised conduction. Microstructural analysis confirmed that manufacturing routes directly influence fibre arrangement and polymer distribution, resulting in distinct electrical responses across the investigated materials.
This study also identified limitations in conventional conductivity measurements, particularly related to geometric assumptions and thickness variability, and proposed a normalisation approach to reduce associated uncertainties. Furthermore, finite element modelling of inductive heating demonstrated that the strong anisotropy of UD TPC tapes limits the formation of effective eddy currents, leading to poor heat generation compared with more isotropic laminate configurations.
Overall, this work establishes a direct link between manufacturing, microstructure, and electrical behaviour in UD TPC tapes. The findings provide valuable insights for improving material characterisation, enhancing modelling accuracy, and enabling practical applications such as in-situ quality control during tape manufacturing and optimisation of induction-based processing techniques.
...
The increasing use of thermoplastic composites (TPC) in aerospace structures calls for a better understanding of their functional properties, particularly for unidirectional (UD) tapes. These materials offer advantages in automated manufacturing and weldability, but their electrical behaviour is inherently complex due to strong anisotropy and microstructural variability. This study therefore investigates the relationship between manufacturing route, microstructure, and electrical conductivity of UD TPC tapes, with an outlook on their applicability in the induction welding process.
A multi-method experimental approach was adopted, combining six-probe electrical measurements, infrared thermography, eddy current testing, and optical microscopy. Four different UD TPC tape systems, produced via distinct manufacturing routes, were characterised and compared. The results demonstrate that electrical conductivity is primarily governed by fibre volume fraction, but is significantly influenced by microstructural features such as fibre distribution, polymer-rich regions, defects, and thickness variations. Deviations from idealised models, such as the Rule of Mixtures, highlight the importance of local fibre connectivity and interfacial effects in determining conductive behaviour. Infrared thermography and eddy current testing revealed that electric current pathways are highly dependent on both internal architecture and surface condition, with polymer-rich layers limiting current injection and promoting localised conduction. Microstructural analysis confirmed that manufacturing routes directly influence fibre arrangement and polymer distribution, resulting in distinct electrical responses across the investigated materials.
This study also identified limitations in conventional conductivity measurements, particularly related to geometric assumptions and thickness variability, and proposed a normalisation approach to reduce associated uncertainties. Furthermore, finite element modelling of inductive heating demonstrated that the strong anisotropy of UD TPC tapes limits the formation of effective eddy currents, leading to poor heat generation compared with more isotropic laminate configurations.
Overall, this work establishes a direct link between manufacturing, microstructure, and electrical behaviour in UD TPC tapes. The findings provide valuable insights for improving material characterisation, enhancing modelling accuracy, and enabling practical applications such as in-situ quality control during tape manufacturing and optimisation of induction-based processing techniques.
A multi-method experimental approach was adopted, combining six-probe electrical measurements, infrared thermography, eddy current testing, and optical microscopy. Four different UD TPC tape systems, produced via distinct manufacturing routes, were characterised and compared. The results demonstrate that electrical conductivity is primarily governed by fibre volume fraction, but is significantly influenced by microstructural features such as fibre distribution, polymer-rich regions, defects, and thickness variations. Deviations from idealised models, such as the Rule of Mixtures, highlight the importance of local fibre connectivity and interfacial effects in determining conductive behaviour. Infrared thermography and eddy current testing revealed that electric current pathways are highly dependent on both internal architecture and surface condition, with polymer-rich layers limiting current injection and promoting localised conduction. Microstructural analysis confirmed that manufacturing routes directly influence fibre arrangement and polymer distribution, resulting in distinct electrical responses across the investigated materials.
This study also identified limitations in conventional conductivity measurements, particularly related to geometric assumptions and thickness variability, and proposed a normalisation approach to reduce associated uncertainties. Furthermore, finite element modelling of inductive heating demonstrated that the strong anisotropy of UD TPC tapes limits the formation of effective eddy currents, leading to poor heat generation compared with more isotropic laminate configurations.
Overall, this work establishes a direct link between manufacturing, microstructure, and electrical behaviour in UD TPC tapes. The findings provide valuable insights for improving material characterisation, enhancing modelling accuracy, and enabling practical applications such as in-situ quality control during tape manufacturing and optimisation of induction-based processing techniques.