PSI - Issue 41

592 A.M. Ignatova et al. / Procedia Structural Integrity 41 (2022) 589–597 4 Ignatova A.M., Yudin M.V., Voronov V.L, Ignatov M.N., Gladky I.L., Inozem sev A.A., Naimark O.B. / Structural Integrity Procedia 00 (2019) 000–000

Fig. 2. Potassium fluorphlogopite sample after fracture.

A 23 mm steel ball (Steel 20) was used as a projectile. The fracture fragments velocity was determined on the basis of a video recording obtained with Photron Fastcam SA5 high-speed camera. The maximum filming speed of the camera was 775,000 frames per second at a resolution of 128×24 pixels. To obtain high quality video footage with short exposure times, the high-speed video recording system was equipped with a lighting unit consisting of seven light sources of 1,000 watts each. The video footage was processed using frame-by-frame image analysis method of ImageJ-FiJi software product (TrackMate module). The trajectory of each fracture fragment was traced in provisional coordinates, followed by determination of the distance covered by the fragment from frame to frame, and next, taking into account the time scale of the video, determination of fragments velocity at a certain moment of time. In order to take into account the individual properties of fracture fragments, size range of fragments has been established in frame-by-frame image analysis using the same ImageJ-FiJi software product (Analyze Particles module). Sample fracture with a steel ball has been performed at a pneumatic test unit (Fig. 3). The steel ball was accelerated in a pipe with the inner diameter of 25 mm and the length of 3950 mm using pneumatic equipment – a 5.2L pump with a high pressure receiver. The receiver was filled with compressed air using a high pressure compressor. Ball velocity was registered using a measurement system based on capture of time when the impactor crosses the control section of the movement trajectory limited by a net of laser beams in the beginning and end of the trajectory. The video recording process is triggered by a signal generated by an automated testing system.

Fig. 3. Pneumatic unit for acceleration of a steel impactor.