PSI - Issue 68

Nedeljko Vukojević et al. / Procedia Structural Integrity 68 (2025) 379– 385 N. Vukojević et al. / Structural Integrity Procedia 00 (2025) 000–000

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A preliminary investigation of the form and degree of the polynomial function for describing the process was applied. In general, the polynomial expression of the second degree describes the observed processes well enough, and the expression is of the following form: . ... (8) For the analysis of the relationship between input parameters ( R eH , D, t ) and the output quantity - objective functions ( KV and K JIc ) - the same initial form of the regression model of linear form was used, and optimization was carried out through the later 'stepwise' analysis regression model and number of parameters. 3.1. Analysis of the results for the total impact energy As the first output function of the goal, the dependent function KV was analyzed - values of total impact energy in the observing points of the experimental model. Based on the 'stepwise' analysis, the final mathematical form of the regression equation is created, which describes the considered process with sufficient reliability. ... (9) The coefficient of determination is R 2 = 0.905. The statistical characteristics of the regression model PRESS RMSE, RMSE, R 2 and PRESS R 2 indicate a satisfactory match between the real data of the experiment and the 'predicted' data. ! ! ! "" ## !! $$ #!#! #$#$ !$!$ %# & ! ' $ () *+ *+ *+ *+ *++ *++ *++ *+ *+ *+ = + + + + + + + + + ! "# "# $ %&D()*H ,(D)D - ,(,D*! . /0(/%0 1 ,(,),& - 1 ,(,,!* . 1 )()D* 1 = + ! " ! + ! " ! ! " ! ! " !

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Fig. 2. 'Surface response' diagram: (a) R eH x t parameter; (b) D x t parameter relationship

Some variables were excluded because the dispersion analysis concluded that their influence is insignificant, such as, parameters R eH 2 , D 2 , relations R eH x D . Fig. 2 shows the 'surface response' for the combination of influential treated parameters of the R eH x t experiment, where the spatial-surface representation of the change in the value of the output