3.2.2. Set of P2P3P4 Connections

The promising results obtained for the first set prompted us to extend it with data related to the P4 connection, which differed not only in the dimensions of the front plate, but also in the class of screws. Training patterns in this case were separated as follows: learning was performed on patterns from P2 and P3 connections (i.e., P2 = {S2, S4, S5}, P3 = {S4, S5}), while testing and validation involved a set of patterns related to P3 and P4 connections (i.e., [P3 = {S2}, P4 = {S2}], and P4 = {S4, S5}, respectively). An example of the results obtained from testing and prediction is shown in Figure 10. As before, there is good agreement between the measured axial forces F2 and the values estimated by the ANN (Figure 10a). The predicted values of the forces in the S3 screws (which were not equipped with force sensors) for all three connections are shown in Figure 10b. The nature of their changes is similar to the other bolts in the analyzed connections.

**Figure 10.** The results of force identification: (**a**) testing; (**b**) prediction.
