Experimental studies of the effect of steel damage on the patterns of surface waves propagation

The issue of monitoring the process of damage accumulation by controlling the acoustic properties of a metal is considered. The aim of the work is to develop an ultrasonic technology that is applicable in production conditions to assess the technical condition of a metal before it is destroyed. The possibility of creating a "damage indicator" was investigated using a high-frequency elastic surface wave as a sensor. The ultrasonic sounding technology used in this work was focused on expanding the spectrum of the probing signal by making it possible to improve the accuracy of measurements. As a parameter characterizing the internal friction, the shape of the acoustic probing pulse is used and, alternatively, the time of passage of a fixed distance in the metal by the wave. Demonstration experiments were carried out on flat samples from pre-annealed steel grade St10. Cyclic tests were carried out using a universal test machine from Tinius OIlsen Ltd., model H100KU providing a load measurement error of 0.5%. The samples were subjected to 50 cycles of soft loading with a voltage amplitude in the cycle of 0.6; 0,7 and 0,8 of the conditional yield point at a constant rate of movement of the active grip of 5 mm/min. The inversion of the observed signal from the amplitude change in time to the amplitude distribution and obtaining (on the basis of this inversion of the parameters) a priori of the chosen statistical Dirichlet distribution model are at the heart of the technique aimed at analyzing the shape of the probing pulse. The change in the stress of loading in the cycle leads to a significant change in the parameter of self-organization of the shape of the probing signal, while there is no significant change in the propagation velocity of the surface wave for different loading regimes. The results demonstrate the possibility of characterizing the value of the elastic hysteresis, which is one of the measures of internal friction in solids by measuring the shape coefficient of the acoustic probe pulse of surface waves.