An automated ultrasonic immersion technique for the determination of three-dimensional elastic constants of polymer composites

Abstract

Abstract An automated, ultrasonic immersion system based upon an original National Physics Laboratory design has been built and evaluated. Ultrasonic transducers operating at a frequency of 2.25 MHz have been used to investigate both tensile and shear velocities in fibre reinforced composite samples. The automation of the system allows fast and efficient large area scanning to be performed. Hence both large-scale, spatial variations in the tensile velocities can be investigated and also, all of the three-dimensional elastic moduli of fibre-reinforced polymer composites can be deduced by monitoring the variation of ultrasonic velocity with angle of incidence on orthogonal planes. Preliminary results indicate that the system will yield most of the three-dimensional elastic moduli to absolute accuracies of better than ± 1 % and in the fast scanning mode, will detect spatial variations of the time-of-flight of ultrasound with a fractional timing error of ± 0.001%. Work is in progress to correlate the ultrasonic propagation to three-dimensional mesostructural features. An automated, two-dimensional image analyser has been developed in-house and a Noran, three-dimensional confocal laser scanning microscope system is being automated at Leeds to determine the three-dimensional fibre orientation states and voidage within composite samples. Therefore it will soon be possible to evaluate existing models linking three-dimensional mesostructure to ultrasonic propagation and the stiffness constants of anisotropic materials.