## 3 Experimental Results
It is only possible to assume that a greater force and a longer exposure time to the corrosion solution support the development of a crack in the material. Of course, the structure of the material also influences this phenomenon. Figure 8 confirms this assumption. The results of the signals of Specim 4, immersed in the solution for a period of \(t_{2}=12\) h with an applied force \(F_{2}=1.5\) kN, are  
Figure 6: Graph of the absolute value of the voltage phasor of Specim 2 corrosion crack. Figure 7: Graph of the absolute value of the voltage phasor of Specim 3 corrosion crack. lower than the previous signals of Specimens 2 and 3. It follows that a longer exposure time to the corrosion solution affects the propagation of the crack. It is visible on points no. 2, no. 8, no. 10, and no. 11, whose values are at the level of the signal value from point no. 5 for Specim 2 and Specim 3. Figures 9-11 show the absolute values of the signals of Specim 5, Specim 6, and Specim 7. From these signals, it is possible to read that the exposure time has a positive effect on the formation of the crack. With different exposure times and force \(F_{3}\) = 1.8 kN, the signal values decreased. Figure 8: Graph of the absolute value of the voltage phasor of Specim 4 corrosion crack. Figure 9: Graph of the absolute value of the voltage phasor of Specim 5 corrosion crack. However, if the results of specimens 5, 6, and 7 are compared with the results of specimens 2, 3, and 4, the result will be a non-linear relationship between the strength and the values of the signals. Since at force \(F_{2}\) = 1.5 kN, the values of the signals are lower than at force \(F_{3}\) = 1.8 kN. It is, therefore, possible to assume a non-linear relationship even with a force of \(F_{1}\) = 1.2 kN. From the results plotted in Figure 7, it is also possible to see that the value of the signal from point no. 1 dropped to the maximum level of point no. 10, which is the assumption that corrosion is spreading in this direction. In the area of higher frequencies, however, it rose compared to other values. This phenomenon can indicate either the absence of a crack at this point on the surface or just below the surface of the material specimen. Or the presence of another discontinuity in the material. A better representation of the eleven points is offered by maps that are drawn on a color scale. The maximum value is searched for in the resulting signals, which are displayed on the map in the field of the corresponding measuring point. The fields representing the measurement points are assigned a color from the color scale based on the value. Figure 12b shows the map of the maximum values of Specimen 2, and Figure 12c shows the map for Specimen 3. Both specimens were in the corrosion solution for the same  
Figure 4:0 Graph of the absolute value of the voltage phasor of Specimen 7 corrosion crack. Figure 4:1 Graph of the absolute value of the voltage phasor of Specimen 6 corrosion crack. time \(t_{1}=6\) h. The specimens differ in the force applied to the specimen in the solution. In Specimen 2, the signal from point no. 5. At this point, corrosion has most affected the structure of the material. From the drawing of the map of Specimen 3, the corrosion affected a larger area but with less intensity than in Specimen 2. In Figure 12d,e are drawn maps of specimens that were in the corrosion solution for \(t_{2}=12\) h. These are Specimen 4 and Specimen 5, respectively. In Specimen 4, there was a larger surface disturbance compared to Specimen 5. The crack in Specimen 6, Figure 12f, is deeper than the crack in Specimen 5 and extends mainly to the area of point No. 5  
The results from Specimen 4, Figure 12d, show the spread of the crack in the direction of points no. 10 and no. 11. On Specimen 7, Figure 12g, the effect of corrosion is visible in points No. 2, No. 5, and No. 8. However, it is clear from the map that the crack partially extends into the areas of points No. 1, No. 10, and No. 11.