PSI - Issue 28

V.V. Sudin et al. / Procedia Structural Integrity 28 (2020) 1637–1643 Sudin V.V./ Structural Integrity Procedia 00 (2019) 000–000

1641

5

Fig. 4. (a) load-displacement curve of a specimen with a high energy of the final fracture after the formation of a brittle crack. The area corresponding to the energy of fracture prior cleavage is shaded in gray. (b) the fracture of the specimen corresponding to the load-displacement curve. temperature shows that for the studied materials, the maximum force is achieved when the pendulum deflects about 4 mm, which corresponds to the depth of a ductile crack of about 1.3 mm. Thus, the main work on fracture resistance is performed with a small initial part of the ductile crack. This initial section makes a small contribution to the area of the shear fracture of the specimen, but it is of primary importance for reliability assurance of the material. In turn, the ductile final fracture and the area of the shear lips, formed after reaching the maximum on the dynamic curve Tanguy et al. (2005), make a large contribution to the shear fracture area of the specimen, but their formation consumes a relatively small amount of energy – up to 30% in the case of the base metal and up to 40% in the case of the weld metal (table 1).

Table 1. Results of Charpy tests Metal

Specimens in transition region

Specimens in danger zone

Percentage of specimens in danger zone, %

Average contribution of final fracture in total energy of fracture, %

Welding method №1 Welding method №2 Welding method №3 Welding method №4 Welding method №5 Welding method №6

74 66 72 61 72 81 83 42 39 20

1 9 8 4 0 1 0 3 0 0

1.4

13.8 19.9 32.2 39.6 21.3

13.6 11.1 24.6

15

5.6 0.0 0.5 0.0 7.1 0.0 0.0

5.9 7.2

HAZ 09G2S QT HAZ 09G2S N

203

10.8 29.3

17G1S

09G2S N 09G2S QT

2.8 7.2

This observation is explained by the fact that at the initial stage of deformation, the movement of the pendulum is accompanied by plastic deformation of the specimen of the initial section. As the crack develops, the specimen cross section decreases, which leads to a decrease in force. When a brittle fracture is formed, the cross-section of the specimen decreases sharply and the value of the specific work of the formation of a ductile final fracture also decreases due to a decrease in the volume of the material subjected to plastic deformation during bending. Thus, as the ductile crack grows, the specific energy of its movement decreases and the most significant decrease occurs at the moment of formation of a brittle crack.