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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Fig. 5. The constitutive dependences (a) and load – displacement curves for uniaxial tensile test: experimental and calculated with different constitutive dependences (b)

4. Results of numerical calculation of the stress and strain in front of a crack

Fracture process of S355JR steel was studied for three characteristic fracture mechanisms, which occur in ferritic steels – fully brittle, mixed brittle-ductile and completely ductile. Fig. 6 presents three load-displacement diagrams recorded during specimens testing which correspond to the fracture process by these mechanisms. If fracture is fully brittle, the cracking occurs without (or with negligible) plastic deformation of the specimens (Fig. 6a). In the case of the mixed brittle – ductile mechanism realization, a significant plastic deformation is observed at the load displacement diagram of the specimen (Fig. 6b) before brittle fracture occurs. Here, conditions for the implementation of brittle fracture are met only after significant plastic deformation of the tested specimen. A typical diagram of completely ductile specimen fracture is shown in Fig. 6c. The share of plastic deformations in the process of specimen fracture is very high while the conditions for brittle fracture realization have not met. In order to accurately analyze the cracking processes and the development of stress and strain fields, numerical calculations were performed at various stages of specimen loading. Marking on the load-displacement graphs of Fig. 6 (Pi) indicate the points in which numerical calculations were performed. The results of calculations in the form of distributions of stress and strain components for the specimens tested at respective temperature are shown in the drawings in the further part of the article.

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Fig. 6. The load-displacement dependences for specimens tested at different temperature: (a) T = – 120 0 C; (b) – 80 0 C; (c) 20 0 C

The stress components distribution before the crack tip in the plane of symmetry (in the middle plane) of SENB specimen tested at temperature – 120 0 C for the specimen fracture (for P1) are shown in Fig. 7a. The stress in the direction along crack extension denoted as  11 , the stress in direction perpendicular to crack plane –  22 , and the stress in specimen thickness direction –  33 . Stress level  22 is higher than in other components of stress. Because