A sandwich-transducer technique for measurement of internal dynamic stress

A technique for the measurement of internal dynamic stresses in rods is described and experimental results are presented. The technique utilized a piezoelectricquartz-crystal disk with a concentric guard ring scribed on each side through conductive plating. The transducer was sandwiched with epoxy adhesive in a Hopkinson-pressure-bar arrangement to compare its output from the center electrode area with surface-mounted strain gages. Preliminary tests showed good peak-stress agreement between the two and pulse shapes were also found to be identical. The effect of bonding on the piezoelectric constant was also investigated. This constant was found to be about 8 percent greater than the accepted value for alpha quartz. This difference was attributed to radial effects.