Measuring Dislocation Density in Aluminum with Resonant Ultrasound   Spectroscopy
  Dislocations in a material will, when present in enough numbers, change the speed of propagation of elastic waves. Consequently, two material samples, differing only in dislocation density, will have different elastic constants, a quantity that can be measured using Resonant Ultrasound Spectroscopy. Measurements of this effect on aluminum samples are reported. They compare well with the predictions of the theory. 
Felipe Barra, Andres Caru, Maria Teresa Cerda, Rodrigo Espinoza,   Alejandro Jara, Fernando Lund and Nicolas Mujica