PSI - Issue 30

A.A. Alexeev et al. / Procedia Structural Integrity 30 (2020) 1–5 A.A. Alexeev et al. / StructuralIntegrity Procedia 00 (2020) 000–000

2 2

the transition of the crack from straight-line propagation to the branching mode is the critical value of the crack propagation velocity V* (limiting velocity), which depends on the material. The measurements of the crack branching velocity were mainly carried out on model materials - polymers by Serensen et al. (1970), Ravi-Chandar and Knauss (1984), Kobayashi (1985), Sharon and Fineberg (1996), Bediy (1991), Sheng (1999), Naimark (2000), Uvarov (2000). Investigation of the process of crack propagation and branching in a structural material such as steel was carried out for example by Finkel (1970) and Duffy (1969), but them was not performed the crack branching velocity measurements.

Nomenclature V

crack velocity, m/s crack length, mm critical crack velocity

L

V* G*

energy of the material’s resistance to the growth of a single crack

2. Equipment and materials To experimentally determine (measure) the velocity of a crack in steels during the transition of a crack from straight-line propagation to the branching mode, a series of tests was carried out to fracture by internal pressure of steel thin-walled cylindrical shells (vessels). ). Shells made of a seamless pipe (steel 20) with a length of 1500 mm, diameter of 159 mm, wall thickness 5 mm, with two welded spherical bottoms 5 mm thick. In the central part of the shell, an artificial defect was applied - a longitudinal notch with a depth, width 1.5 mm, length 50 mm. The vessel was loaded with internal pressure as a result of the expansion of freezing water, liquid-filled and sealed vessel cooled at a negative temperature until it fracture (Fig. 1).

Fig. 1. General view of fracture of the vessel.