Acoustic anisotropy and dissolved hydrogen as an indicator of waves of plastic deformation

The method of acoustoelasticity is an ultrasonic method of nondestructive testing based on measurement of acoustic anisotropy, which is defined as the relative difference between the velocities of plane transverse ultrasonic waves of mutually perpendicular polarization. In contrast to the methods of tensometry, the method of acoustoelasticity allows one to obtain average values of mechanical stresses along the thickness of the material. Comparative studies of the distributions of acoustic anisotropy and concentrations of dissolved hydrogen were obtained for specimens from rolled commercial alloys in the case of large plastic deformations and after their destruction. The significant influence of microcracks on acoustic anisotropy was revealed. A new formula for the dependence of acoustic anisotropy on initial texturing, stresses, localized plastic deformations and microcracks is proposed. The theoretical model based on the concept of local surface microcracking was constructed. It allows us to explain the correlation between the distributions of acoustic anisotropy and hydrogen concentrations. Analytical expressions for the relation between the velocities of ultrasonic waves and components of the damage tensor were obtained. This makes it possible to evaluate the damage based on the anisotropy of the acoustoelastic properties of the material. The results of the investigation allow us to propose a new method for identifying the regions of localization of plastic deformations, microcracking and local zones with increased hydrogen concentration.