PSI - Issue 5

Jan Kec et al. / Procedia Structural Integrity 5 (2017) 340–346 Jan Kec, Ivo Cerny / Structural Integrity Procedia 00 (2017) 000 – 000

344

5

Fig. 6 Dent A: Stress – strain curve at operating pressure Fig. 7 Dent B: Stress – strain curve at operating pressure The second part of the test consisted of the cycling by internal overpressure with maximum value 6,3 MPa and minimum value close to the zero pressure. Total number of cycles with these parameters was 10 000. (10 000 cycles with these parameters were applied). Strain gauge measurements were carried out always after 2000 cycles. Fig. 8 shows the increment of deformation on strain gauge 23. Therefore, the effect of pressure cycles resulted in the change of the dent A profile. Deformation fluctuations can be attributed to temperature changes in the laboratory.

Fig. 8 Evaluation of residual stress after various pressure cycles The following burst test was performed with continual measurement of deformations of dents at gradual increase of the internal pressure up to to the fracture of the body. During the test, two dwells at 66 % yield point and at 100% the yield point were carried out. Loading rate was about 4,5 bar/min. Deformation behaviour of both dents can be seen in Fig. 9 and 10.

Fig. 9 Dent A: Stress – strain curve during burnst test

Fig. 10 Dent B: Stress – strain curve during burnst test