It follows from the obtained

It follows from the obtained distributions that the trends discovered in the early loading stages became persistent and unambiguous: the magnitude of acoustic anisotropy in the regions of maximum plastic strain exceeded that of the anisotropy in the midpoints of the working area by nearly two times (see curves 2 and 3 in Fig. 4). Analysis of the measured velocities of the plane transverse ultrasonic wave polarized along the direction of the applied load, V1, allows to assess the wave\'s overall behavior during cyclic elastic-plastic strain. Fig. 5 shows the V1 velocity curves at the stages prior to sample fracture. As noted above, in order to measure acoustic anisotropy, it is sufficient to measure the propagation time of ultrasonic waves, which was achieved in all 1–23 points. The thickness of the examined region also needs to be measured to calculate the velocities. However, the curvature of the surface in points 1, 2 and 22, 23 was such that it proved impossible to measure the thickness with the required accuracy. For this reason, Figs. 5 and 6 show the distributions of ultrasonic wave velocities only in points 3–21. The measurement results obtained allow to conclude that, firstly, the transverse wave velocity V1 is not only non-constant, but actually exhibits ezh2 pathway of monotonous increase and decrease. Secondly, this velocity has a clear decreasing trend in the regions of higher plastic strain and directly near the site where the neck formation and sample fracture occurred. Finally, the behavior of velocity variation correlates to that of acoustic anisotropy variation in the sample as a whole. This indicates a macroscopic process affecting the entire working area of the sample. Further investigation of the decrease in the transverse wave velocity V1 in the regions of high plastic strain and near fracture sites can be valuable in developing techniques for detecting the areas of critical stress and strain in the structural elements diagnosed. The distribution curves for the velocity of the transverse wave polarized perpendicularly to the direction of the applied load, V2 (Fig. 6a), and for the velocity of the longitudinal ultrasonic wave V3 (Fig. 6b) were also obtained for these points at similar measurement stages. As in the case of transverse velocity V1, they are not constant quantities and have both regions of monotonic decrease and monotonic increase. While an overall decrease can be ascertained for the longitudinal wave velocity around points 9–21, corresponding to the midpoints of the working area and the region of high plastic strain, Maternal inheritance currently seems impossible to draw any clear conclusions about the transverse wave velocity V2, despite the qualitative similarities in the constructed curves. Additional experiments are required to study the variation in the transverse wave velocity V2 and the longitudinal wave velocity V3.
Conclusion The largest values of acoustic anisotropy were obtained in the regions of the highest plastic strain in the sample. Similar patterns were observed both for the longitudinal wave velocity V3 and for the transverse wave velocity V1, polarized along the direction of the applied load.
Acknowledgment
Introduction The basic principles of the acoustoelastic method were laid down by Benson and Raelson in their major study [1], published in 1959 and concerned with assessing the stress-strain state of standard steel samples with a prismatic cross section under uniaxial loading. The effect discovered by the authors was the linear dependence between the propagation velocities of transverse elastic waves polarized in mutually perpendicular directions and the applied stresses. One of these waves was parallel to the direction of the applied load, and the other was perpendicular to it. This phenomenon has been named the acoustoelastic effect. Unlike other acoustic techniques, the acoustoelastic method allows to assess the stress-strain state. The key qualitative and quantitative characteristic of the acoustoelastic method is the acoustic anisotropy parameter determined by the following formula: