The Morphology of the Hertzian Cone in Plate Glass by Projectile Impact
A.Miyamoto and Y.Murakami
Abstract:Plate glasses of windows and doors of buildings are often destroyed by the bullets in the criminal cases using firearms. When a plate glass is impacted by a projectile, the Hertzian cone is produced behind the impact point of this glass. It is known that the apex angle of the Hertzian cone crack in Pyrex glass caused by small steel ball impact varies in a systematic manner with the impact velocity. However, there are few reports especially on the results caused by the lead bullet impact. In order to obtain the basic data to estimate the impact velocities and the incident angles of the projectiles, an experiment about the morphology of the Hertzian cone was carried out. In the experiment, projectiles (11mm dia. Steel balls and 0.38 inch (9mm) dia. Lead bullets) were shot onto the float plate glasses (soda-lime glasses). A strong correlation was found between the ratio of the Hertzian cone diameter to the plate glass thickness and the impact velocity. It was also found that the Hertzian cone caused by inclined impact became the size equivalent to the velocity component which is normal to the glass surface. Thus, the morphology of the Hertzian cone can be one of the indexes for estimating the impact velocities and the incident angles of the projectiles. Key Words:Hertzian cone , Plate glass , Projectile impact , Fracture , Impact velocity, Incident angle