AUTOMOBILE SIDE GLAZING is generally composed of ∼4 mm thick sheets of either tempered safety glass (TSG) or laminated safety glass (LSG), and also demonstrates simple or complex curvature. TSG indicates a single piece of thermally treated glass possessing substantially higher mechanical strength than annealed (stress-free) glass. When broken at any point, the entire piece spontaneously breaks into small blocky particles. LSG indicates two pieces of glass bonded by an intervening layer of specially formulated plastic. It will break under sufficient loading, but the shards tend to adhere to the polymer interlayer, which also provides a barrier to penetration. Most of today's passenger vehicles come equipped with TSG, but LSG is increasingly being used for its safety and convenience benefits. The base material used for both types of glazing is annealed soda-lime glass with various additives (e.g., calcium, iron, copper), and it is generally tinted either green for solar load reduction, or gray for lites behind the B-pillar for privacy. (Pillars are bars that are located at the upper side of the vehicle separating the front and rear window, windshield, at the rear glass of the vehicle. The B-pillar is located between the side of the driver and the rear passenger.) This glass is made by the float process that was developed by Sir Alastair Pilkington in 1959 (Pilkington PLC, 2000). The process consists of drawing molten glass in a continuous ribbon across a vat of molten tin to produce a more uniform, flaw-free product than the plate glass process that it replaced. Upon exiting the tin bath, the glass goes through an annealing lehr. Automatic cutters remove the edges and cut the product to length for further processing. Annealed glass can be drilled, given edge preparations, heated and bent, tempered, laminated or given coatings. Monolithic annealed glass is rarely used in modern vehicles because of its low strength and undesirable fracture characteristics. The U.S. regulation governing the design of automobile glazing is found in the Federal Motor Vehicle Safety standards at 49 CFR 571.205, Glazing Materials (2001), which indicates that one purpose of the standard is to "minimize the possibility of occupants being thrown through the vehicle windows in collisions." This safety consideration is particularly important since, although a consistent majority of rollover fatalities were determined or believed to have not been wearing their seatbelts, a substantial 28% were, in fact, restrained but died anyway (Deutermann, 2002). The standard that governs material selection for automotive glazing is ANSI/SAE Z26.1-1996. This is a material standard, and does not govern the safety performance of the glazing system made from the material that is specified. The automotive glazing system comprises the transparent window proper, a regulator system including mounting brackets if it is moveable, plus any edge fixation and/or framing.
Tempered glazing is the dominant glazing for sidelights---as it has been since the early 1960s when it largely displaced laminated glass in these positions. Although chemically strengthened glazing has been used on a limited scale, thermal tempering is the preferred process.
