2.1. The testing theory of acoustoelasticity
Acoustoelasticity theory is one of the main bases of ultrasonic stress testing. Acoustoelasticity theory is based on
the finite deformation of continuum mechanics to study the relationship between the elastic solid stress state and the
macroscopic elastic wave velocity. Based on the four basic assumptions of acoustoelasticity, the elastic wave
equation (acoustoelasticity equation) in stress medium under initial coordinates can be obtained [8].