PSI - Issue 14

Shashidhar Naik H. G. et al. / Procedia Structural Integrity 14 (2019) 900–906 Shashidhar Naik H. G. et.al./ Structural Integrity Procedia 00 (2018) 000–000

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2.3. Strain Energy Release Rates

The values of SERR in the three modes of fracture, were computed using the basic principle of MVCCT. Total Strain Energy Release Rate, G T was calculated as the sum of the values of SERR in the three modes. The effective strain energy release rate, G EFF is defined as the ratio of the nodal strain energy release rate to the critical strain energy release rate. The critical value of SERR, G C was computed using the equations obtained by B-K law [Benzeggagh and Kenane, (1996)]. The crack was said to propagate when the ratio of G T/ G C reaches unity. 3. Results and Discussion A parametric analysis was carried out to compute the SERR along the delamination front. The delamination sizes were varied from 10 mm to 100 mm at the interface considered, while the initial displacement is kept constant. The bonding state of the plate post analysis is shown in Figure 3 for an initial delamination size of 100 mm. The contact stresses for all the three modes; opening mode, tearing mode and scissoring mode, for various delamination sizes is presented in the Figure 4. From the plot it can be seen that the contact stresses values increase as the delamination starts to grow. The results of the computed SERR in all the three modes along the delamination front and the combined computed SERR plot for the considered interface are shown in Figure 5. It was evident that Mode III stress was predominant over Mode I and Mode II from the results. G T /G c values were plotted against all diameters of delamination as shown in Figure 6, to predict the point at which the delamination starts to propagate. It can also be noted that the delamination begins to propagate at 90.5 mm. This is the critical delamination size for which the G T /G c ratio reaches unity.

Figure 3. Bond state (BDSTAT) plot for 100 mm delamination size