Out-of-autoclave cure monitoring of CFRP laminates using an innovative and low-cost electrical system.
Topic(s) : Manufacturing
Co-authors :
Huikangyue BAO (FRANCE), Philippe MARGUERÈS (FRANCE), Philippe OLIVIER (FRANCE)Abstract :
In the context of carbon fibre reinforced polymer (CFRP) manufacturing process, conventional online cure monitoring techniques are usually based on expensive measurement systems using dedicated sensors. In this work, an innovative real-time cure monitoring method using electrical impedancemetry (EI) and the self-sensing material is introduced.
In a recent previous work [1-3], we studied phases transitions in CFRP during their curing by EI showing that changes in the electrical complex impedance Z can easily be related to those of conventional parameters such as the thermoset matrix degree of cure alpha. This work was carried out using a commercial single-channel impedance analyzer: HIOKI. In addition to its high acquisition cost, this device presented certain limitations in terms of measurement channels (only one) and data acquisition rate (60s for a frequency sweep).
These facts led us to develop a new EI measurement bench for monitoring the impedance changes in CFRP part for aeronautical applications (airframe structures). The innovative new multi-channel (8) bench we designed and manufactured is based on the Digilent PmodIA module (never used previously for this purpose) and an Analog-Front-End (AFE) developed for EI measurements. It costs only 15% of the HIOKI analyzer and has a data acquisition rate 48 times higher (1,23 s versus 60 s). All this while maintaining an equivalent impedance measurement range: 100mOhm to 1MOhm.
This approach not only makes it possible to monitor the degree of cure α (DOC) by the EI and the oven temperature, but also to detect potential cure cycle issues. The sweep frequency response analysis of the material (using impedance modulus |Z| and argument θ and their time derivatives during curing), enables the identification of the most critical points of polymerization: Liquefaction (PL), Gelation (PG), Vitrification (PV) and Finish of reaction (PF) (See Table and Figure).
The presence of carbon fibres results in a significative difference between the unreinforced resins and the composites in their cure behaviour. Compared to the results of a preliminary study, a similar behaviour is obtained on different CFRPs (commercial references Hexcel composites T700/M21 and CTMI NC66/1808NA laminates) using two different benches, highlighting the value of the proposed approach. The EI results are in good agreement with α obtained by rheometer and differential scanning calorimetry (DSC).
The experimental validation of our approach will contribute to the Structures Health Monitoring (SHM) of CFRP and the functionalization of carbon/epoxy composites. These results will be used in future works for refining electrical-mechanical modelling not only during curing but also during mechanical loading.
In a recent previous work [1-3], we studied phases transitions in CFRP during their curing by EI showing that changes in the electrical complex impedance Z can easily be related to those of conventional parameters such as the thermoset matrix degree of cure alpha. This work was carried out using a commercial single-channel impedance analyzer: HIOKI. In addition to its high acquisition cost, this device presented certain limitations in terms of measurement channels (only one) and data acquisition rate (60s for a frequency sweep).
These facts led us to develop a new EI measurement bench for monitoring the impedance changes in CFRP part for aeronautical applications (airframe structures). The innovative new multi-channel (8) bench we designed and manufactured is based on the Digilent PmodIA module (never used previously for this purpose) and an Analog-Front-End (AFE) developed for EI measurements. It costs only 15% of the HIOKI analyzer and has a data acquisition rate 48 times higher (1,23 s versus 60 s). All this while maintaining an equivalent impedance measurement range: 100mOhm to 1MOhm.
This approach not only makes it possible to monitor the degree of cure α (DOC) by the EI and the oven temperature, but also to detect potential cure cycle issues. The sweep frequency response analysis of the material (using impedance modulus |Z| and argument θ and their time derivatives during curing), enables the identification of the most critical points of polymerization: Liquefaction (PL), Gelation (PG), Vitrification (PV) and Finish of reaction (PF) (See Table and Figure).
The presence of carbon fibres results in a significative difference between the unreinforced resins and the composites in their cure behaviour. Compared to the results of a preliminary study, a similar behaviour is obtained on different CFRPs (commercial references Hexcel composites T700/M21 and CTMI NC66/1808NA laminates) using two different benches, highlighting the value of the proposed approach. The EI results are in good agreement with α obtained by rheometer and differential scanning calorimetry (DSC).
The experimental validation of our approach will contribute to the Structures Health Monitoring (SHM) of CFRP and the functionalization of carbon/epoxy composites. These results will be used in future works for refining electrical-mechanical modelling not only during curing but also during mechanical loading.