A New Polycarbonate and Glass Laminate and its Affects on the Relationship Between Residual Tensile Stresses and Impact Resistance of Windshields

Current windshield manufacturing processes produce residual tensile stresses near the edges of windshields. This residual tensile stress reduces the ability of the windshield to withstand suddenly applied external loading over a short time interval near the edge.

Present manufacturing processes can reduce some of the residual tensile stress produced during the annealing process, but currently it is technically difficult to eliminate.

However, an innovative and more cost-effective solution for the residual tensile stress problem has been proposed. Application of a thin film of polycarbonate around the perimeter of the windshield allows the energy generated during impact loading to be dissipated without the need to change the windshield’s material properties.

This paper presents the Knott Laboratory findings and conclusions generated from impact testing six different windshields, at nine perimeter impact locations protected by the polycarbonate film and none unprotected perimeter control impact locations per windshield.