High-frequency Optimally Windowed Chirp rheometry for rapidly evolving viscoelastic materials: application to a crosslinking thermoset
arxiv(2024)
摘要
Abstract
Knowledge of the evolution of mechanical properties of the curing matrix is
of great importance in composite parts or structure fabrication. Conventional
rheometry, based on small amplitude oscillatory shear is limited by long
interrogation times. In rapidly evolving materials, time sweeps can provide a
meaningful measurement albeit at a single frequency. To overcome this
constraint we utilize a combined frequency and amplitude-modulated chirped
strain waveform in conjunction with a home-made sliding plate piezo-operated
(PZR) and a dual-head commercial rotational rheometer (Anton Paar MCR 702) to
probe the linear viscoelasticity of these time-evolving materials. The direct
controllability of the PZR resulting from the absence of any kind of firmware
and the microsecond actuator-sensor response renders this device ideal for
exploring the advantages of this technique. The high frequency capability
allows us to extend the upper limits of the accessible linear viscoelastic
spectrum and most importantly, to shorten the length of the interrogating
strain signal (OWCh-PZR) to sub-second scales, while retaining a high
time-bandwidth product. This short duration ensures that the mutation number
(NMu) is kept sufficiently low, even in fast curing resins. The method is
validated via calibration tests in both instruments and the corresponding
limitations are discussed. As a proof of concept the technique is applied to a
curing vinylester resin. The linear viscoelastic (LVE) spectrum is assessed
every 20 seconds to monitor the rapid evolution of the time- and
frequency-dependence of the complex modulus. Finally, FTIR spectroscopy is
utilized to gain insights on the evolution of the chemical network while the
gap-dependence of the evolving material properties in these heterogeneous
systems is also investigated.
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