Estimation of adhesive bond strength in laminated safety glass using guided mechanical waves: Part I. An energy velocity approach

Laminated safety glass is used in the automobile industry and in architectural applications. Laminated safety glass consists of a plastic interlayer, such as a layer of poly vinyl butyral (PVB) or Butacite, surrounded by two adjacent glass plates as shown in Figure 1. The glass can be float glass, plate glass, tempered glass, or sheet glass, and the plastic interlayer is made of a viscoelastic material with relatively high damping(1,2). Typical thickness values of the glass plates and PVB interlayer are given in Table 1. The level of adhesive bond strength between the plastic interlayer and the two adjacent glass plates has a significant role in the penetration resistance against flying objects and is a critical parameter towards ensuring the proper performance of safety glass(1,2). Penetration is prevented primarily by absorbing the kinetic energy of the projectile by stretching the plastic interlayer, partial delamination between the plastic interlayer and the two adjacent glass plates, and by the fracture surfaces generated in the two adjacent glass plates. Laminates with very high adhesion levels fail in a quasi-monolithic plate-like mode; the plastic interlayer is stressed beyond its rupture strength and is cut and torn by pieces of glass. For laminates with low adhesion levels, large shards of glass delaminate from the plastic interlayer increasing the risk of injury from impact. An optimal level of adhesion is then required for the safety glass to absorb enough of the impact energy to prevent projectile penetration, while simultaneously preventing the plastic interlayer from being stressed beyond its rupture strength. For these reasons, estimation and control of adhesive bond levels in laminated safety glass is a critical issue.