Experimental Study of the GFRP Perforation Stochasticity Near the Ballistic Limit

The work aims at experimentally analyzing features of the impact interaction of a steel spherical projectile with glass fibre-reinforced plastic (GFRP) specimens with the thicknesses of 4 mm, 6 mm, and 7.3 mm at the velocities near the corresponding ballistic limits. The experimental study was carried out in two stages. At the first stage, ballistic curves, estimations of V50 and limit perforation and non-perforation velocities were obtained based on the results of the first series of impact tests using the Lambert-Jonas approximation. At the second stage, a series of tests was carried out for GFRP specimens of each thickness, when the initial projectile velocity was selected so that it fell into the zone of mixed results to obtain the perforation frequency curves. Based on the results of more than 300 experiments, it was established that the perforation frequency curves for GFRP specimens with the thicknesses of 6 mm and 7.3 mm can be obtained using the normal distribution law. Also it was found that the ratio of the width of the zone of mixed results to the corresponding V50 estimation for two thicknesses of specimens was about 4%, which is significantly less than the scatter of the strength characteristics of GFRP specimens obtained during the static tests.