CHARACTERIZATION OF PARTICLE IMPACT BY QUANTITATIVE ACOUSTIC-EMISSION

Acoustic emission (AE) is proposed as a method of monitoring hard particle impact on surfaces. In a preliminary study, small spherical particles of nominal diameter 53-63 μm and 75-90 μm of bronze and glass respectively were dropped in vacuum onto steel or aluminium target plates at selected velocities between 2.5 and 7.1 m s-1. At these low velocities the collisions are entirely elastic and no erosion occurs. However, a quantitative AE signal analysis method was developed which enabled various parameters from the particle impacts to be determined, with the potential for measuring the degree of plasticity of impact in later experiments. AE signals were detected with a calibrated broad bandwidth piezo-electric transducer positioned on the opposite face of the target plate at the impact epicentre. The Green's function for the plate, together with the AE transducer and system response obtained by calibration using a capacitance transducer, were deconvolved from AE signals to yield the impact force function of the particle impact. The velocity dependence of the impact time and peak impact force thus determined agreed with that predicted from semi-empirical models of elastic particle impact. The absolute magnitude of these two parameters also compared very well with theoretical values. The quantitative acoustic technique developed was capable of sizing the particles, and the results compared favourably with the particle size distribution measured optically, giving the correct mean particle diameter to within 10% and the distribution spread to within 26%. This fundamental approach provides a framework for later extension to plastic and partially plastic particle impact Thus the technique could be developed for on-line erosion monitoring. © 1990.