PSI - Issue 13

Ivica Galić et al. / Procedia Structural Integrity 13 (2018) 2109 – 2113 Galić et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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Fig. 3. Internal crack location and dimensions for DN50 PN160 valve body

3. Results and discussion

A comparison of SIF values obtained through FEM and X-FEM for the internal crack of a DN50 PN160 valve is presented in Figure 4. Here, the change in the stress intensity factor is observed as a function of the angle φ .

Fig. 4. Changes of SIF values along crack tip

From Fig. 4 it is evident that the values of SIF obtained by X-FEM are slightly greater than the values calculated with the classical method. Shapes of the curves are approximately the same and the maximum value of SIF, calculated as an average value of the first five contours, is approximately 11% higher for X-FEM than the maximal value obtained by the classical FE method. When SIF is obtained as an average value while neglecting the first contour, the difference is only 1.2%. Based on the greater values of the stress intensity factors shown in Fig. 4, it can be concluded that the life assessment obtained by using stress intensity factors obtained through X-FEM will be shorter than life assessment obtained by the classical FE method. Therefore, it is justified to use X-FEM for complex shapes like valve bodies, since a more conservative prediction can be made.