Smart Cure Monitoring Method of Carbon/Epoxy Laminates Using Electric Capacitance Change with Applied Alternating Current Frequency

Abstract

Authors have developed an electric resistance change method for delamination monitoring of carbon/epoxy composite laminates. The method employs reinforcement fibers as sensors; electrodes are co-cured. Co-cured electrodes for delamination monitoring are adopted in the present study as sensors for monitoring the degree of cure. This study proposes a new method using electrical capacitance change for monitoring the degree of cure without using additional sensors. Applying alternating current between electrodes during the cure process provides dielectric properties of carbon/epoxy composites. As with the conventional cure monitoring method using extra dielectric sensors, the degree of cure of composites is monitored by measuring the dielectric constant of composites. The dielectric constant of epoxy resin changes concomitant with change of frequency of applied alternating current (AC). Using dependency of the applied AC frequency of the dielectric constant, the degree of cure is measured directly. The proposed method is applied to single and multi-ply carbon/epoxy composite laminates. The method demonstrates excellent estimations of the degree of cure without additional sensors.

Carbon fibres reinforced composites. Electrical impedance analysis: a gateway to smartness

“…A large number of references have been given in subsection 1.1. Nevertheless, when focussing upon electrical measurement methods for cure monitoring it appears that some authors measured electrical resistance [103][104], dielectric constants [105][106][107], or more recently electrical impedance [108][109][110][111]. One of the advantages of electrical impedance (Z) -using its modulus |Z| and argument θ measurements (eqs.1, 2 and 3) -lays in the fact that both resistance (carbon fibers and contacts between adjacent carbon fibers) and capacitance (thin zone of insulating matrix) are scanned (see Figure 3).…”

Preliminary experimental study on the electrical impedance analysis forin-situmonitoring of the curing of carbon/epoxy composite material for aeronautical and aerospace structures

“…The monitoring of this resistance during the curing process thus needs to be accompanied by monitoring of capacitance, so as to take account of the changes in capacitive conduction in the polymer: notably between plies and between packets of fibre. The modulus of the impedance keeps behaviour of firstorder (whatever the phase of the resin) which can be simply modelled by an R-C parallel equivalent electrical model, as described in figure 3 [31]. This model is all the more legitimate because access resistances are negligible with respect to the composite resistance as described above.…”

“…Among the many existing sensors, impedancemeasurement sensors, which measure low-and high-frequency impedances to determine respectively the resistance and the capacitance [30,31], have been little used up to now as integrated sensors to monitor manufacturing and the integrity of the material over its life cycle. With the addition of multi-physical sensors (electrical, mechanical and thermal) to these impedance-measurement sensors, it is possible to envisage a global instrumentation, both sensitive and robust, for monitoring the manufacturing and life cycle of the product.…”

Cure Monitoring of Composite Carbon/Epoxy through Electrical Impedance Analysis

“…Ryan, Carolyn and Karim (2002) propose to use the measurement of the capacitance as an indicator to reduce the curing time; but notify the need of further studies to determine a relationship between the change of capacitance and temperature or the degree of cure. Inada and Todoroki (2005) use two electrodes placed on the surface of the material. They consider the material as a parallel RC circuit and perform a frequency analysis of the dielectric permittivity to study the change of the capacitance.…”