PSI - Issue 41

A.M. Ignatova et al. / Procedia Structural Integrity 41 (2022) 589–597 593 Ignatova A.M., Yudin M.V., Voronov V.L, Ignatov M.N., Gladky I.L., Inozemtsev A.A., Naimark O.B./ Structural Integrity Procedia 00 (2019) 000–000 5 The potassium fluorphlogopite sample was fixed in the holder of the test unit so that only one of the sample's ends was rigidly fixed. Four impact tests have been conducted with the following parameters: ball velocity 230 m/s, collision angle 90º; ball velocity 120 m/s, collision angle 90º; ball velocity 230 m/s, collision angle 30º; ball velocity 120 m/s, collision angle 30º. As an alternative to a frontal impact at an angle of 90º, an impact angle of 30º (Fig. 4) was selected as it was experimentally proven earlier (Ignatova et al.) that this setup creates rebound conditions and change in the trajectory of the projectile.

Fig. 4.Scheme of the steel ball impacting the target at an angle of 30º.

Results and discussion. Fig. 5 shows frames from the video footage that correspond to various collision parameters. The following phenomena complicating the analysis of the video footage have been discovered in the course of the video processing:  rotation of fracture fragments during fragmentation field emission;  shimmering of fracture fragments during rotation (caused by the properties of the material);  secondary acceleration of fragments in the stream of the compressed air accelerating the impactor. In order to avoid the influence of these factors, data on zero velocities and sharp velocity fluctuations have been excluded from the results of frame-by-frame analysis, assuming that they were caused by secondary phenomena. Figures 6 and 7 show diagrams describing the change in the velocity of fragments during the first 4 µs after collision. The obtained dependencies are hyperbolic. A relatively wide spread in velocity values of individual fragments is due to the difference in size. Fig. 8 shows diagrams of fracture fragments particle size distribution in each of the experiments; the data is summarized in Table 1. Since the particle size determines the mass and, hence, initial kinetic energy, the table also contains calculated values of kinetic energy of fragments (minimum, maximum and average).