PSI - Issue 16

Ihor Dzioba et al. / Procedia Structural Integrity 16 (2019) 97–104 Ihor Dzioba, Sebastian Lipiec/ Structural Integrity Procedia 00 (2019) 000 – 000

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a

b Fig. 8. The opening stress component (a) and strain (b) distributions before of crack tip at T = – 80 0 C

Next situation of stress and strain distributions (Fig. 9) accorded to completely ductile crack growth (Fig. 3c) which was recorded during specimen tested at 20 0 C. Qualitatively the evolution of the stress  22 distributions is similar as in the previous case, but the level of the stress  22 value is lower. Maximum stress value reaches the level about of 1450 MPa (Fig. 9a). While the level of strains in the area before the crack tip is similar to the previous one.

b

a

Fig. 9. The opening stress component (a) and strain (b) distributions before of crack tip at T = 20 0 C

5. Conclusions

Based on the experimental and numerical calculation results obtained in this study some conclusions are presented. Implementation of the fracture process in the material is possible after reaching certain critical levels of mechanical fields in local areas. Brittle fracture takes place if a high level of normal stresses is reached in the local material area, but strain has low level. For the tested steel S355JR, the level of critical stresses should be in the range of 1500 ÷ 1600 (MPa). The lower level chosen such, because at 1450 MPa (tested at T = 20 0 C) brittle fracture did not take place, and in the case of a fully brittle fracture (at T = – 120 0 C) the values of stress before tip crack exceeds 1500 MPa. The higher value was estimated, based on results specimen tested at mixed brittle-ductile fracture (at T = – 80 0 C). In this case maximum of stress  22 is equal of 1650 MPa, but critical value must be lower, because they act in a certain area. Whereas the level of plastic deformation in this area is very low, namely lower than