PSI - Issue 39

Viktor Morozov et al. / Procedia Structural Integrity 39 (2022) 432–440 Author name / Structural Integrity Procedia 00 (2019) 000–000

437

6

generated in the sample with EEW or with cut and its propagation reinitiated and controlled during tests. Paths of the crack propagation with various lengths plotted for the second approach. The first approach allowed us to reveal the dependence between crack propagation velocity and amplitude of loading presented in Fig. 7, and next to determinate boundary failure stress amplitude, which was 70 MPa by linear extrapolation the dependence to zero crack velocity.

Fig. 6. Characteristic mechanical pulse waveform in PMMA lamel sample.

Visual control of PMMA cylinder samples revealed system radial cracks growing from the whole line of the explosion channel to the outer surface of the sample (Fig. 8) and perpendicular to the ends of the cylinder. Relatively thin samples were fractured into two or mere fragments by that cracks. Failure of thin samples may be explained by the fact that radial pressure in the cylinder decreases in the radial direction.

Fig. 7. Dependence between crack propagation velocity and amplitude of applied pulse loading in tests with PMM lameles. Crosses demonstrate obtained in tests results and straight line is extrapolation to achieve boundary value of amplitude.

The nature of the cracks system in fluoroplastic samples was dramatically different (Fig. 9). The grid of short cracks growing from the explosion cannel along its line initiated on the first step. And in the second step, these cracks grow to the outer surface of the cylinder. These cracks may merge and produce general cracks propagating along the generatrix of the cylinder and causing its failure.