PSI - Issue 20

4

A.A. Alexeev et al. / StructuralIntegrity Procedia 00 (2019) 000 – 000

A.A. Alexeev et al. / Procedia Structural Integrity 20 (2019) 254–258

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Fig. 3. Trajectories of the movement of cracks in PMMA samples: the top row is at +20 C without crack branching, the bottom row is at -60 C with crack branching

On the basis of works carried out by Serensen et al. (1970), Ravi-Chandar and Knauss (1984), Sharon and Fineberg (1996), Bediy (1991), Naimark and Uvarov (2000), it was established that the parameter controlling the transition of a crack from straight propagation to branching mode is the critical (limiting) value of the crack propagation velocity V* =500 – 800 m/s in brittle plastics. However, the limiting value of the crack velocity at multiple branching with parallel movement of the front of several cracks V* =750 – 920 m/s, consistent with the data of above works with branching single crack V* =500 – 800 m/s, shows that excess energy entering the crack tip is used to create new cracks, and not to increase speed. It has been hypothesized that the criterion of crack branching is the achievement of the critical (limiting) value of the crack propagation velocity ( V* =500 – 800 m/s in brittle plastics), both when branching a single crack and when multiple branching with parallel movement of the front of several cracks. These results confirm the hypothesis proposed earlier by the authors of the physical mechanism of crack branching, where the achievement of the critical velocity V* for crack branching is a sufficient condition, and the necessary condition is that the energy flow to the top of a moving crack exceeds the energy of a single crack G* .