The damage threshold of laminated glass structures

The effect of varying the thickness of the individual glass layers on the impact resistance of a range of laminated glass constructions has been examined. Chippings, similar to those used in traditional road construction, have been accelerated to velocities in excess of 20 m/s using a purpose-built catapult system. Tests have been conducted at both normal and 45 degrees angles to the surface of the glass laminate and the critical velocity for damage initiation, V-crit, determined. The results of this low velocity study indicate that the thickness of the outer glass is the primary parameter in determining V-crit, whereas the inner thickness has a secondary influence on this threshold. Off-axis impact testing has shown that it is the normal component of the impact velocity that determines the damage threshold. A detailed optical inspection of the failed laminates highlighted a change in fracture mode from flexure-induced star cracking to top surface cone cracking as the overall laminate thickness is increased. (C) 1998 Elsevier Science Ltd. All rights reserved.