## 4 Results and Discussion
An increase in the load in the contact of the tool with the treated surface is accompanied by an increase in friction powers, causing the dissipation of vibrational energy, which is especially noticeable in the high frequency range. 2. An increase in frictional powers between the surfaces of the tool and the workpiece causes heating of the surfaces. This can lead to a decrease in the mechanical properties of processed material, which reduces the proportion of brittle fracture in favor of the viscous mechanism during chip formation. Brittle cracks are characterized by a high speed of crack movement and short pulses that create amplitude spectra propagating into the high frequency range. Viscous cracks have a significantly lower rate of development and form longer pulses, producing smaller amplitudes at high frequencies. 3. Changes in the rigidity of the elements of the elastic system, including the tool, the part, and mechanisms for their mounting. An increase in cutting powers during wear of the cutting edge can cause mobility in the joints of parts, leading to an increase in the duration of pulses accompanying the formation of chip elements. To substantiate the first mechanism, Figure 17 shows how the amplitude of the AE signal changes in different octave bands when the grinding wheel on a flat-grinding machine (Figure 3) comes into contact with the workpiece. In Figure 17, the value \(\delta\) shows a decrease in the initial amplitude A. Their ratio \(\Delta\) as a percentage reflects the impact of frictional interaction on the AE signal. When the tool and the workpiece come into contact, the interaction of the grinding wheel grains is present, and friction does not have time to form yet. Still, at subsequent moments, normal loads and a corresponding friction power arise in the contact. This immediately affects the amplitude of the AE signal, but in different frequency ranges, and the result of a decrease in amplitude is different. Figure 17 shows the percentage reduction in RMS of AE amplitudes for seven octaves. For the lower three octaves, there were no noticeable changes, and friction did not affect the AE signals in these frequency ranges. Further, the percentage decrease in amplitude increased from octave to octave. In the 32 kHz octave band, the amplitude dropped by 82%. The shown change in the composition of the acoustic signal indicates that in the state  
Figure 17: The proportion of decrease in RMS amplitude (\(\Delta\)) in octave frequency bands when the grinding wheel and the workpiece come into contact. of close contact between the tool and the workpiece, the pulses of interaction between the grinding grains and the workpiece become longer. As the contact density increases, surface irregularities transform into a state close to all-round compression, which prevents the formation of brittle cracks, and the pulses become longer. In this case, the interaction energy is distributed over a more extended period, which reduces the power density. The second mechanism is associated with a temperature change that increases with friction. An increase in temperature affects the mechanical properties of materials, such as hardness and elastic modulus. In metals, an accelerated decline in mechanical properties begins in the region of temperatures 0.5 from the melting temperature [59]. Changes in the parameters of the AE signals when the temperature of the tool and workpiece changes under the impact of friction powers can be traced when turning steel workpieces at different speeds. Figure 18 shows recordings of the high-frequency AE signal during face turning at constant speeds with an increasing cutting speed due to transverse feed towards the periphery. Figure 18a shows a recording of a VA signal in the frequency range of 7-10 kHz when turning NiCr20 TiAl steel [54] at relatively low speeds. Figure 18b shows a similar record, but at increased cutting speeds of 41 Cr54 steel. Figure 18a shows that with an increasing cutting speed, the signal amplitude increases almost linearly.