Acoustic Waveguide Cure Curves for Materials Ranging from Fast Cure Resins to Slow Cure Concrete

The attenuation and transmission velocities of ultrasonic waves traveling through curing polymers are related to the three general phases of curing which can be categorized as; increasing viscosity; gelatinization (the transition from a liquid state to that of a rubbery gel), and hardening (increasing modulus). This should be expected because the acoustic wave transmission in materials depends upon their molecular structure which is related to the material viscosity, density and modulus. In 1952 Sofer and Hauser [1] passed 2.3 Mhz longitudinal ultrasonic waves through curing polymers and related attenuation and velocity measurements to the degree of cure. However, wave dispersion can be a problem with this technique and an improved approach is to use embedded acoustic waveguides to guide the ultrasonic waves through curing polymers. A step in this direction was taken by Roth and Rich [2] in 1953 who developed a 28 kHz ultrasonic technique for measuring viscosity during the polymerization of plastics. They used a thin metallic strip into which shear waves were magnetostrictively induced and when this strip was immersed in a viscous liquid, the attenuation of the shear waves traveling along the strip could be related to the liquid viscosity. This metallic strip can be considered to be an acoustic waveguide (AWG) excited and measured from one termination. Later, in 1971, Lynnworth[3] and in 1974, Papadakis [4] developed AWG techniques using magnetostrictive activation of torsional waves and applied their methods to curing polymers.