In this paper, quasi-normal air-coupled ultrasonic (ACUS) spectroscopy has been applied to monitor the ultraviolet (UV) curing of a vinyl ester resin. The technique is useful for measuring, with a fast single measurement, compression properties since the beginning of curing and shear properties after the gel point. Data analysis must consider the temperature variation of the system, the air and the support plate, induced by the exothermic nature of curing. Additionally, the evolution of the degree of conversion, measured with a direct current sensor, is done to estimate the variation of thickness of the resin due to the shrinkage and to correlate the mechanical properties with the curing process. Finally, the relationship between the degree of conversion and Young's modulus of a vinyl ester resin during UV curing has been successfully characterized for degrees of conversion higher than the 65%.
Acknowledgements
The authors would like to thank the Government of the Basque Country for the grants received to carry out the PhD theses [grant numbers PRE_2018_2_0009, PRE_2018_2_0208] as well as for the financial support of the project [grant number IT883-16].
