ON THE LOW-VELOCITY IMPACT BEHAVIOR OF GLASS PLATES

Circular plates of float glass with thicknesses between 3 mm and 12 mm and clamped at a radius of 65 mm have been impacted with a 3 mm diameter hardened steel ball travelling at velocities in the range of 10 - 50 m s(-1). The fractures can be classified as Hertzian ring cracks at the contact zone with or without conical fractures; crushed impact zones on the front face which may be accompanied by cone cracks, median, radial and lateral cracking and in some cases star cracks propagating from the rear face. Examples of these will be described together with a qualitative predictive analysis for their occurrence as a function of impact velocity, plate thickness and surface condition. Of particular interest is the observation of crack bifurcation within the cone fractures in plates of thicknesses below 6 mm.