Photographic studies of the normal impact of hard spheres on fused silica generating hertzian cones

• Published in: Journal of non-crystalline solids 2023-09, Vol.616, p.122428, Article 122428
• Main Author: Chaudhri, M. Munawar
• Format: Article
• Language: English
• Subjects: Circularly polarized light; Crack bifurcation; Fused silica; Hertzian cone crack angle; High-speed framing photography; Loading rate; Maximum cone crack velocity; Poisson's ratio; Tungsten carbide projectiles
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2023.122428

•A new experimental approach using circularly polarized light combined with stress-induced birefringence of fused silica has been used in this work to follow, using high-speed framing photography, the damage in fused silica when it is impacted with a 2 mm diameter tungsten carbide sphere travelling at 150 m s−1.•From this arrangement we were able measure more accurately the contact time between the projectile and the silica block, the rayleigh surface wave velocity, the longitudinal wave velocity, the velocity of the hertzian cone cracks generated and the loading time of the projectile.•From this information we were able to calculate the time taken to form very initial ring/cone crack. Then we show the loading rates generated at the time of formation of the cone cracks. We show that the higher is the loading rate, the smaller is the angle of the hertzian cones.•It is suggested that the loading rate affects the poisson's ratio of the glass near the loading area, which controls the angle of the hertzian cone cracks generated. Colour high-speed photographic framing sequences of the normal impact of 2 mm diameter tungsten carbide spheres on a block of fused silica at 150 m s−1 were taken at 1 × 106 frames per second. The initiation and growth of the resulting two coaxial cone cracks, which formed within 0.1 µs of the initial projectile contact, were followed. The innermost cone crack of a semi included angle of 32° travelled at a velocity of (2270± 100) m s−1 which is close to the theoretical maximum crack velocity of 2180 m s−1 in fused silica. Importantly, the semi included angle of the cone crack was about a half of the angle of the cone crack produced by quasi-static loading. A suggested explanation, based on the localized decrease of the target's Poisson's ratio due to the high impact loading rate, has been proposed and examples are given which support this suggestion.