Acoustic characterization of changes in viscoelastic properties of epoxy during cure

The transformation of an epoxy during cure from a viscoelastic liquid to a viscoelastic solid is characterized by the change in the shear and longitudinal ultrasonic velocities and attenuations. The measurement of these ultrasonic properties is reported for several different resins cured at room temperature. The velocities are used to calculate the bulk and shear moduli as a function of cure time. The results indicate a parallel development during cure of the shear and bulk moduli. Measurements of the longitudinal attenuation at several different frequencies indicate the viscoelastic response can be characterized by a single relaxation time which increases as the cure progresses.