PSI - Issue 72

Dražan Kozak et al. / Procedia Structural Integrity 72 (2025) 270 – 277

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4. Analysis of fatigue fractures caused by stone impacts on the diverter pipe and the SINTAP procedure 4.1. Analysis of fatigue fractures caused by the impact of stones on the diverter pipe The greatest stress occurs at the point where stones impact the pipe, leading to a high probability of crack initiation at that location. A numerical analysis was conducted to calculate the stress intensity factor during the second phase of crack growth. It was assumed that a semi-elliptical crack with a major radius of 1 mm and a minor radius of 0.5 mm had been initiated. The crack is positioned on the inside of the pipe, which aligns with the numerical results. Six contours with an element size of 0.04 mm were defined around the crack tip. The analysis determined that the crack grows due to the fatigue of the material. The specified crack, based on the global coordinates, is shown in Figure 6.

Fig. 6. The specified crack based on the global coordinates.

The third phase of crack growth was not considered in this analysis. Defined Paris constants C and m are 1.62∙10 27 ((m/cycle)/(Pa∙m 0.5 )m, and 2.6664. The dominant type of crack opening is defined by the K I factor of stress intensity, as the crack is subjected to tensile loading, resulting in a breakaway type of crack opening. The results of the numerical analysis for the K I stress intensity factor are shown in Figure 7.

Fig. 7. K I stress intensity factor in the 4th crack contour.

The crack in the second propagation phase can propagate by 50.938 mm from its initial size, leading to unstable crack growth and eventual failure of the structure.