PSI - Issue 5

Jan Kec et al. / Procedia Structural Integrity 5 (2017) 340–346

343

Jan Kec, Ivo Cerny / Structural Integrity Procedia 00 (2017) 000 – 000

4

Fig. 2 Measured profile depth of dent A

Fig. 3 Location of strain gauges at dent A

To measure the deformation of dent B, three strain gauges circumferentially oriented were used – Fig. 5. Strain gauges 3 and 4 were situated inside the dent B, strain gauge 5 was located on the edge between the dent profile and unaffected surface. It can be seen from the dent profile that its shape is non-symmetrical. The highest value of the profile depth was reached in the first third of the dent in longitudinal direction (measurement No. 3) and in the second third of the dent in circumferential direction – Fig. 4. The highest measured value of the dent depth was 4,23 mm.

Fig. 4 Measured profile depth of dent B

Fig. 5 Location of strain gauges at dent B

2.3. Pressure test

Pressure test was performed by the internal pressure, as the recommended pressure medium water was used. During the first part of the pressure test, the pressure increased gradually to the operating pressure 6,3 MPa at the rate about 3,5 bar/min., then the 2 minutes dwell at operating pressure level and and the unloading followed. The whole course of measurement was recorded with the help of the measuring equipment. During the continual increase of pressure up to the operating level, all strain gauges on dent A show almost linear course without residual deformations. The higest deformation values were reached in the deepest place of the dent (strain gauges 19, 20), negative deformation values, on the contrary, were observed on the strain gauge situated at the dent edge. The dependences of deformations and internal pressure suggest that the dent has a tendency to decrease its depth - Fig. 6. In case of dent B, during the continual growth of pressure up to the operating level, strain gauges 3 and 4 show linear increase of deformation with two different line slopes. After the unloading, considerable positive residual deformations occurred. However, no line slope corresponds with the theoretical one calculated from Hook law for the biaxial state of stress. On strain gauge 5, two different line slopes with negative deformation values were also observed. After the unloading, they remained negative residual - Fig. 7.