Monitoring the viscoelastic evolution of vinyl ester resins for SMC via non-contact resonant ultrasound spectroscopy

Fernández-Caballero Fariñas, María Dolores; Achiaga, Beatriz; Camacho-Iglesias, Marta; García-Etxabe, Rafael B.

Monitoring the viscoelastic evolution of vinyl ester resins for SMC via non-contact resonant ultrasound spectroscopy

Archivos

fernandez_monitoring_2026.pdf (3.28 MB)

Fecha

2026-10

Autores

Fernández-Caballero Fariñas, María Dolores

Achiaga, Beatriz

Camacho-Iglesias, Marta

García-Etxabe, Rafael B.

Editor

Elsevier Ltd

Resumen

Monitoring the pre-cure maturation of thermosetting resins, particularly in Sheet Moulding Compound (SMC) manufacturing, is critical for ensuring processability and final part quality. This stage involves complex viscoelastic changes driven by ionic thickening, a process often classified using industrial know-how rather than robust quantitative methods. However, current standard characterization methods remain destructive or contact-based, hindering their use for continuous, in-situ monitoring. This study presents a contactless methodology based on Non-Contact Resonant Ultrasound Spectroscopy (NC-RUS), implemented via Air-Coupled Ultrasound (ACU) to monitor the maturation of vinyl ester (VE) resin over a 30-day period. We compared a neat resin control against a formulation thickened with 3 wt% magnesium oxide (MgO). Ultrasonic parameters, estimated from thickness resonance spectra, show that, for the thickened samples, both longitudinal velocity and attenuation increase significantly with time, in contrast to the control samples confirming the ultrasonic sensitivity to the ionic thickening of the VE. Furthermore, the trends in longitudinal modulus and attenuation were validated against a standard curve of apparent viscosity obtained via Brookfield viscometry. This points to a correlation with the phenomenological stages of SMC maturation. These findings show the potential of ACU as a powerful contactless tool for the in-situ monitoring of resin pre-cure state in composite manufacturing.

Palabras clave

Air-Coupled Ultrasound (ACU)
Non-Contact Resonant Ultrasound Spectroscopy (NC-RUS)
Polymer monitoring
Resin maturation
Sheet Moulding Compound (SMC)
Viscoelasticity

Cita

Fariñas, L., Achiaga, B., Camacho-Iglesias, M., & García-Etxabe, R. (2026). Monitoring the viscoelastic evolution of vinyl ester resins for SMC via non-contact resonant ultrasound spectroscopy. NDT and E International, 164. https://doi.org/10.1016/J.NDTEINT.2026.103807

URI

https://hdl.handle.net/20.500.14454/6498

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