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Abstract
Polymeric materials, such as Thermosets, are becoming more widely used in demanding applications due to their ability to tailor the properties of structures while reducing weight and cost. The manufacturing conditions of polymeric materials are critical since they determine the resulting polymer structure, which influences the final properties and performance characteristics. It is essential to monitor these polymers during the manufacturing process to understand the relationship between the fabrication conditions and the final quality of the parts. Although destructive testing is commonly used to characterize polymer properties, this type of testing requires specific sample preparation and geometry. Furthermore, lab-type instrumentation used for destructive testing cannot be taken to the field for in-situ testing.
This work presents three non-destructive evaluation methods to characterize the curing process and the viscoelastic properties of various epoxies. The magneto-electric effect was capitalized by monitoring changes in the surface charge density of dispersed magneto-electric nanoparticles by evaluating the output magnetic signal under an applied magnetic field. This method was used to monitor the curing process of an adhesive as well as the water ingression after exposing the polymer to 95 % relative humidity and 70 ⁰C. Ultrasonics were utilized to evaluate changes in the cure kinetics and final properties of the epoxies due to variations in their polymer chemistry, i.e., different stoichiometries and the presence of a residual solvent. Changes in longitudinal and shear sound speeds proved how the fabrication process influenced the curing and the viscoelastic properties of various epoxies.
The chemical structure during cure was monitored using Fourier transform infrared spectroscopy. The evolution of the polymer’s molecular structure while curing corroborated the trends obtained using ultrasonics. The evaluated curing kinetics were modeled using the Hill equation to better understand numerically the curing processes and allow for future predictions. Combining ultrasonics and FTIR has the potential to effectively characterize the properties of polymers in both an in-field and manufacturing setting, aiding in the tailoring process, and ensuring their reliability in demanding applications.