AN AUTOMATED ULTRASONIC IMMERSION TECHNIQUE FOR THE DETERMINATION OF 3-DIMENSIONAL ELASTIC-CONSTANTS OF POLYMER COMPOSITES

An automated, ultrasonic immersion system based upon an original Natio nal Physics Laboratory design has been built and evaluated. Ultrasonic transducers operating at a frequency of 2.25 MHz have been used to in vestigate both tensile and shear velocities in fibre reinforced compos ite samples. The automation of the system allows fast and efficient la rge area scanning to be performed. Hence both large-scale, spatial var iations in the tensile velocities can be investigated and also, all of the three-dimensional elastic moduli of fibre-reinforced polymer comp osites can be deduced by monitoring the variation of ultrasonic veloci ty with angle of incidence on orthogonal planes. Preliminary results i ndicate that the system will yield most of the three-dimensional elast ic 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 pr ogress to correlate the ultrasonic propagation to three-dimensional me sostructural features. An automated, two-dimensional image analyser ha s been developed in-house and a Noran, three-dimensional confocal lase r scanning microscope system is being automated at Leeds to determine the three-dimensional fibre orientation states and voidage within comp osite samples. Therefore it will soon be possible to evaluate existing models linking three-dimensional mesostructure to ultrasonic propagat ion and the stiffness constants of anisotropic materials. (C) 1998 Els evier Science B.V.