In the recent twenty years, the percentages of occupant deaths that involve ejection have not changed very much although seat belt use has increased from 10% to 66%. Clark (1989) also suggested the use of an 18 kg (40 pound) spherical test object moving at 33 km/h (20 mph) perpendicular to the glazing planes to test the adequacy of the laminate strength, after finding that the maximum “effective mass” of a dummy collapsing against a window glazing approximates that of the 40 pound test weight, and that the preliminary commercial laminated glazing adequately framed could resist ejection at this test speed The T-edge is trapped in the front and rear channels of the window, allowing the glazing to go up and down but preventing the cracked glazing from pulling out of the channels, thus maintaining the ejection reduction quality through the strength of the stretching plastic layer or layers. Also, this and our earlier unpublished work included the development of the “T-edge” encapsulation of the front and rear edges of movable (side window) glazing in order to transfer window loads to the window frame. The earlier work of one of us indicated this need to reduce ejection by returning to laminated glazing, with experiments utilizing the two ply or glass-plastic laminated glazing, with its greater laceration reduction as well as ejection reduction qualities. Passenger cars roll over in crashes less often than light trucks and vans and sport utility vehicles, with about 20 to 25% of occupants killed in all crashes in passenger cars killed with ejection, and about 40% of occupants killed in crashes in light trucks and vans and sport utility vehicles killed with ejection. Of those ejected, about 7500 were killed with ejection through glazing areas, with 5400 of these ejected through the front side windows. Sixty one percent of those killed with ejection were killed in rollover crashes. Of these, 10,900 were killed with whole body or partial ejection, 36% of those killed. For averaged values in the period of 1988–1993, about 30,000 people were killed each year in crashes of light vehicles (passenger cars, and light trucks and vans and sport utility vehicles). It is this occupant ejection component of the glazing failure modes that is the most dangerous aspect of tempered glass. Injuries involving glazing include primarily lacerations from broken glass and ejections through the glazing areas. Note also that a blow with a sharp object, such as an awl or prick punch, can shatter tempered glass with very little energy input. It takes more than three times the kinetic energy of a blunt object to penetrate through a typical laminated glazing than to shatter and penetrate through tempered glass. The laminated glazing may be cracked but the plastic interlayer holds the glass pieces together and keeps the window closed. But when the tempered glass is fractured, it shatters, scattering the glass fragments and opening out the window. This makes tempered glass have a harder surface, resisting fracture when struck by a blunt object under loads that crack the annealed glass of windshield type laminated glazing. The glass is reheated, given the needed curvature in a mold, then blasted on both sides by cool air, causing a shrinkage or compression of the surfaces. The glass is cut to the window size and any necessary holes are cut. In today’s manufacture, molten glass floating on a hot bath of liquid tin, “float glass,” is drawn off on rollers then cooled slowly to become annealed glass. In the United States, the windshield remained of laminated glass, with its ability to prevent the penetration into the occupant compartment of a heavy object that would shatter tempered glass. Tempered glass side and rear windows were gradually introduced in other models and by other manufacturers, essentially replacing laminated side and rear windows by 1961, with contested arguments that tempered glass was better for side windows than laminated glazing. It was first introduced in the United States in a Chrysler model in 1936. Tempered glass for automobiles was developed in Europe, and soon was considerably less expensive than laminated glazing. The plastic interlayer holds together the pieces of glass when broken, greatly reducing the danger. Henry Ford introduced the laminated windshield, first developed in Europe, for the Model T in 1927, and soon after the windows were also with laminated glazing. The first windshields, about 1903 in the United States, and soon after the first glass windows, were of plate glass, which breaks into long, sharp, dangerous shards. Automobile glazing in the United States is primarily the three ply (annealed glass/polyvinyl butyral or PVB plastic interlayer/annealed glass) laminated windshield, and tempered glass side, rear, and roof windows.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |