Experimental Investigation on the Impact of Intact Hailstones on Thin Steel Sheets

Abstract

This paper first outlines a method for producing water-based artificial hailstones that remain intact upon impact on thin steel sheets at high velocities. The objective is to simulate certain natural hailstones that remain intact after hitting steel roofings at terminal velocities, causing greater dents than the hailstones that shatter because more energy is available to damage the steel sheet. The intact (impact-resistant) water-based artificial hailstones were used in a systematic series of impact tests on steel sheets. The variables were diameter of the spherical hailstones (from 25 to 50 mm), impact velocity (20 to 50    m / s ), steel sheet thickness (0.35 to 1.00 mm), and the steel material’s yield stress (300 to 550 MPa). The test results of the intact water-based artificial hailstones are then used to develop three-dimensional (3D)-printed hailstones that can be handled more easily and be reused. It was found that the dent depths incurred by spherical artificial hailstones of the same diameter impacting on flat steel sheets perpendicularly varied slightly less than linearly with their kinetic energy. However, for the same kinetic energy, smaller projectiles caused greater dent depths than larger ones because the dent area caused by a smaller projectile was more localized, so for a given plastic deformation energy of the steel sheet, a smaller dent area requires a greater dent depth. The dent depth caused to a flat steel sheet is therefore a function of the spherical projectile’s kinetic energy (mass and velocity) and diameter, and the sheet steel’s thickness and yield stress. It increases with the increase in the first parameter, and decreases with the increase in the other three. It was demonstrated and explained that the momentum of a projectile may not be an appropriate parameter for determining the resulting dent depth.