The Behaviour of Laminated and Toughened Glass under Static Bending and Impact at Different Velocities

JSGT 1944 V28 T133-T151

The bending of laminated glass with hard cellulose interlayers is not very different from that of sheet glass, .but when a soft vinal interlayer is used the apparent .modulus of elasticity is reduced. This decrease is most marked with small pieces of glass, and tends to the value to be anticipated if the two pieces of glass were independently deformed. When broken under impact just heavy enough to crack at least one of the glasses, laminated glass with a cellulose acetate interlayer again behaves in a manner similar to that of sheet glass. The interlayer resists splintering, however, and the assembly remains a coherent whole until much higher energies of impact are applied than those required to fracture the glass. As this energy is increased further the laminated glass has a tendency to break up into a number of large pieces, that is, to be brittle. This property of brittleness is a variable one, and for any given impact there is a given probability of brittleness. The experiments show that the capacity of laminated glass to resist a blow of a given energy is markedly increased at velocities above 20 mph Under bending, thermally-toughened glass behaves in a manner similar to sheet glass, except that the bending strength is approximately doubled. Under slow impact the strength of the material is also large, but as the incident velocity is increased above 20 mph there is a drastic reduction in strength. The various properties of toughened glass can be quantitatively explained on the assumption that it behaves like sheet glass with a constant compressive stress at the surface.

R. N. Haward