A technique is presented for estimating the state of viscosity of a thermally curing resin. The resin's complex shear modulus at 1 MHz is derived from the measured reflection coefficient of shear wave pulses at the tool-resin interface. A special transducer-buffer assembly that operates at high temperature and provides a reference calibration signal has been developed. With this assembly, absolute determinations are made throughout the cure cycle of the storage (real) and loss (imaginary) components of the shear modulus. The high-frequency dynamic viscosity is calculated from the latter. Comparison with data obtained at low shear rates with a 10-Hz torque viscometer indicates the feasibility of using the high-frequency technique to monitor the rheological properties of thermally curing resins.
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