Dielectric monitoring of cure in a commercial carbon-fibre composite

Watching Orientational Ordering at the Nanoscale with Coherent Anti‐Stokes Raman Microscopy

“…As with the mechanical case, these changes in τ E represent an α relaxation and are related to changes in the glass‐transition temperature ( T g ) of the resin; it has been shown that log τ E is proportional to T , and for a constant cure temperature, the log increases approximately linearly with the cure time 7. A logarithmic plot of the relaxation frequency (1/τ E ) versus the cure time, extrapolated to 1 Hz, gives a useful estimate of the cure time for vitrification of the resin 9. In relation to the real part of the dipolar contribution to permittivity, it has been found that the low frequency value ϵ 0 decreases during the cure and decreases with temperature; the high frequency value ϵ ∞ is independent of the cure time and temperature and typically falls between values of two and four units.…”

“…Many physical methods have been applied to the monitoring of thermoset curing, principally in laboratory studies. Two prominent macroscopic methods are the measurement of dielectric permittivity3–14 and the recording of ultrasonic wave propagation parameters, the most basic of which are the compression wave absorption coefficient and the phase velocity 15–20. Another method that has frequently been applied is differential scanning calorimetry (DSC), either alone21, 22 or in combination with dynamic mechanical analysis (DMA),23 dielectric measurements,24 or ultrasonic studies 25.…”

Dielectric non-destructive testing approach to cure monitoring of adhesives and composites

“…A range of model systems have been reported and include rubber modified-carboxy terminated acrylonitrile butadiene (CTBN)-epoxy resin [35,36], and thermoplastic modified resins used in aircraft manufacture [37][38][39]. A number of studies have attempted to establish correlations between the dielectric data and other physical measurements of the cure processes of resin [40][41][42][43][44][45], glass [46], and carbon fibre [47][48][49][50]. In the latter case, it has been possible to use the conducting characteristics of the carbon fibres to explore the cure at various points in the CFRP resin matrix [50].…”

Monitoring cure and detecting damage in composites with inductively coupled embedded sensors

“…The high cost and complexity associated with autoclave processes (and many other methods of composite manufacture), have created demand for techniques capable of providing real time data during cure, to ensure that parts are fully cured in the minimum amount of time. Numerous cure monitoring methods exist of which measurements of the dielectric permittivity [11,12,13,14], and ultrasonic techniques [12,15,16] are two of the most prominent macroscopic scale approaches, whilst differential scanning calorimetry (DSC), can be used to analyse the behaviour during cure of small laboratory samples (measuring tens of milligrams) [15,17,18]. All of these techniques can provide detailed analysis of the curing process, but each requires specialist equipment which can be of considerable expense; ultrasonic techniques often require transducers to be embedded into the tooling [19,20], whilst measurements of the dielectric permittivity are typically recorded by embedded sensors which become redundant post manufacture [14,21].…”