Abstract: An ultrasonic viscometer is described which is particularly designed for monitoring the viscosity of a thermally curing resin or composite, such as a fiber-reinforced epoxy composite, in an autoclave at high temperature. According to a preferred embodiment, the viscometer comprises a piezoelectric element of lithium niobate crystals bonded to a first buffer of copper, which is bonded on the other side to a second buffer of aluminum. The resin or composite is in contact with the second buffer. When the transducer emits a short ultrasonic pulse, two echoes are reflected back, the first echo being generated by the copper-aluminum interface, the second by the aluminum-resin interface. The signals from the two echoes are processed to obtain the complex reflection coefficient at the interface of the second buffer and the resin, from which the viscosity of the resin can be calculated and the cure state of the resin determined.

Abstract: Disclosed is a method for determining the dispersion of a surface acoustic wave in an object, including the steps of generating a broadband acoustic wave in a surface of the object, detecting the wave at first location on the surface, and detecting the wave at a second location on the surface. Fourier transforms of the first and second detected waves are calculated, then the change in phase .DELTA..phi.(f) of the frequency component f of the detected wave, between the first and second locations, is computed from the phase components of the quotient of the two transforms. The dispersion of the wave in the surface is given by the formulav(f)=(2.pi.f .DELTA.l/.DELTA..phi.(f))In a pulse-echo version of the method, the wave is generated and detected at the first location, and generated and detected at the second location, the dispersion then being according to the formulav(f)=4.pi.f .DELTA.l/.DELTA..phi.(f)).

Abstract: Disclosed is a method for measuring the depth a of a surface flaw in an object, including the steps of irradiating the flaw with an incident acoustic surface wave signal, detecting a reflected acoustic surface wave signal, including a first portion reflected from the surface edge of the flaw and a second portion reflected from the bottom of the flaw, and analyzing the interference between the first and second portions of the reflected signal to determine the depth of the flaw. The analysis may be carried out by Fourier transforming the reflected signals from the time domain to the frequency domain, selecting a frequency f.sub.n for which a maximum or minimum amplitude is detected independent of the angle of detection, and calculating the depth a from the formula a=nV.sub.r /2f.sub.n, where n is an integer, and V.sub.r is the speed of an acoustic surface wave in the object.