Design Considerations for Lightweight Windshields

The car of the future must not only meet stringent emissions standards, it must be more fuel efficient and cost less without compromising occupant safety. Much progress has been made in reducing emissions via improved engine designs, better engine control systems, and advanced catalyst technologies. Initial assessment by MIT researchers shows that by 2020, conventional vehicles will be twice as fuel-efficient, half as polluting and cost little more. This paper, which is in support of the goals of PNGV (Partnership for New Generation of Vehicles), focuses on lightweight glazing of the future car with the targeted weight reduction of 30% to help improve corporate average fuel economy. To this end, much work has been carried out in designing and testing the conventional laminated safety windshield which accounts for 62% of the total glazing weight. Since occupants' safety is of utmost concern, lightweight designs must be optimized in terms of strength, fatigue, impact resistance, laminate geometry and orientation, and their overall contribution to structural stiffness of the vehicle frame. The paper compares the mechanical properties of tin vs. air side of soda-lime-silica float glass - notably strength, fatigue, hardness and elastic modulii - which are influenced by surface composition and which figure heavily in lightweight windshield design. Similarly, the edge finish of individual glass plies as it affects the strength and safety of the final product is addressed. The contribution of glazing to vehicle stiffness, which affects occupants' safety, is also discussed. The paper concludes with the acoustic damping requirements which pose a serious challenge for lightweight glazing system for the car of the future.