Mechanism of defect creation on sheet glass by particle impact and its influence on stray light

Abstract

Stray light on the windshields of automotive vehicles, caused by the impact of small particles, imposes severe safety hazards during night driving. Due to reduced contrast by stray light, nonilluminated objects are perceived much later than through pristine windshields. The objective of this paper therefore is to show the dependence of stray light on impact velocity, impact angle, particle shape and the mechanical properties of the impacting particle and the target material. Single and multiple impacts of SiC (≈1 mg/particle) and quartz sand (≈ 0.7 mg/particle) on ordinary and strengthened float glass under angles of 30°, 45° and 90° and velocities between 50 and 200 km/h were investigated. Profilometer and various methods of stray light measurement, such as total integrated scattering, were used. Based on the correlation between surface roughness and stray light, it can be proved that the amount of stray light is proportional to the ratio of impact volume to the area of the undamaged surface. Caiculating the contact pressure during impact on the target for Sharp and rounded particles in dependence on velocity and impact angle and applying the fracture mechanical criteria for the formation of lateral cracks allows the modeling of the impact volume for the various combinations of particle and target contacts and thus an estimation of the stray light to be expected. Comparison of the model calculation with experimental data exhibits good agreement. Both sets of data show an increase in the amount of damage with increasing velocity and steeper impact angle. The damage caused by SiC is always more severe than the damage by quartz sand. Increasing the fracture toughness of the target material reduces the extent of the damage by about 10%. Α more pronounced reducdon of stray light and mechanical deterioration of up to 60% in comparison to normal float glass can be achieved by a newly developed composite material, consisting of a 0.2 mm thick glass, a 0.36 mm thick layer of PVB, and a float glass Substrate of 3 mm thickness.