Method for monitoring the mechanical state of a material

A simple but precise method is described for simultaneously measuring the flight times for shear and longitudinal ultrasonic pulses. This measurement can be used to calculate the average tensile or compressive stress component along the propagation path because the two sound speeds depend differently on stress. It can also be used to monitor the ductilities of structural components because the modulus ration G/B which can readily be derived from the two flight times is a measure of the ease of plastic flow relative to the ease of brittle fracture. As an example, it is shown that as a tool steel becomes more ductile during tempering after quench hardening, its G/B ratio decreases. Also, it is shown that G/B varies systematically with atomic number, and that f.c.c. metals with small G/B are ductile but those with high G/B are intrinsically brittle.