The three-dimensional elastic constants of materials can be measured using the ultrasonic immersion method.
Knowledge of the elastic constants can be used to feed back into models of the material's behaviour or that of the composite manufacturing process used.
By rotating the sample, time of flight measurements can be obtained a range of angles of incidence, typically up to 40 degrees.
From the time of flight, the phase velocity can be determined as a function of the angle of incidence of the ultrasonic pulse.
Using Christoffel's equations, the measured data can be fitted using a least squares numeric method to determine six of the nine elastic constants.