An empirical method for correcting dispersion in pressure bar measurements of impact stress

Abstract

The dispersion of stress waves in pressure bars distorts a propagating stress pulse, and hence limits the accuracy with which dynamic stress can be measured. This dispersion is caused by a frequency dependence of phase velocity, and previous methods of dispersion correction have adjusted the phase shift of dispersed frequency components using a theoretical bar characteristic. However, the effectiveness of these schemes with more than a small amount of dispersive distortion is very limited. A new method of dispersion correction described in this paper is based on a bar phase characteristic which is derived from measured stress pulses arising from the impact of very small spheres. Examples are given of reconstructing impact stress from a range of particle sizes, showing that the method is very effective even with large amounts of dispersive distortion.