PSI - Issue 33

Vitor E.L. Paiva et al. / Procedia Structural Integrity 33 (2021) 159–170 Author name / Structural Integrity Procedia 00 (2019) 000–000

167

9

cycle. For Specimen #20, the critical point was located on the left side of the rim. Strains were slightly higher than the one located on the right side. Thus, a crack is most likely to start at this critical point. For the case of Specimen #21, after 10 cycles of observation, both critical points showed similar behavior. This DIC acquired strain information was also verified by the optical fiber Bragg strain gage sensor readings, as shown in Figures 13 and 14. These strain gage sensors (Fiber Optic Bragg Sensors) were bonded to locations close to the anticipated critical points identified by DIC analysis performed during previous tests carried out to quickly identify the critical points on the specimens. One can see that the resultant measurements agreed well with those obtained using the DIC analysis. 3.2. Buried tests After the specimens were buried, they were firstly loaded during five cycles with the same pressure ranges used in the in-lab tests. Strains at the hot-spots actuating in the case of specimens #20 and #21 are presented in Figures 11 and 12 for the in-lab and buried tests. Only three cycles were plotted for clarity purposes. One can see that the influence of the soil restraint on the deformation of the dent area is minor by comparing the circumferential strains actuating at the hot-spot locations under the in-lab and buried conditions. Quantitative strain measurements for these conditions are given in Table 1 for these two specimens and for others where those measurements were carried out.

Fig. 11. Circumferential strain variation along three cycles of pressurization at the most-strained points in Specimen #20 (a) DIC before burying (b) FBSG before burying (c) FBSG after burying.

Fig. 12. Circumferential strain variation along three cycles of pressurization at the most-strained points in Specimen #21 (a) DIC before burying (b) FBSG before burying (c) FBSG after burying.