Abstract

Nondestructive Stress State Evaluation Using Acoustoelasticity Phenomenon

N.Nikitina (Nizhny Novgorod Branch of Blagonravov Mechanical Engineering Research Institute of Russian Academy of Sciences, Nizhny Novgorod, Russia)

e-mail: wvs@dynamo.nnov.ru

Taking into account nonlinear terms in the wave equation, one may find the dependence between the velocity of elastic waves and the values of mechanical stresses. So, two pure shear waves exist, which propagate normally to the load direction, and the relative value of their velocities difference is proportional to the difference of in-plane principal stresses. However, the directly measured ultrasonic wave parameter isn't the velocity, but (for example) the propagation time, the thickness of testing material also varies when the stresses are varied. Therefore, one must have three, not two, equations in order to determine each principal stress. The solution of this problem is based on the use of the longitudinal wave propagated across the plane of stress acting. The combined equations for the case of in-plane (biaxial) stressed state of initially anisotropic plate are proposed. Special piezoelectric transducers are used to generate and receive ultrasonic pulses of smooth envelope and main frequency equal to 2-10 MHz. Time-of-flight measuring with relative error equal to 0.005% is provided for longitudinal and shear ultrasonic pulses. The values of the acoustoelastic coefficients of engineering metals and alloys are experimentally determined. So, the evaluation of the mechanical stresses by the ultrasonic method is provided.

Section : 3