Post-Lamination Response of Warm-Bent Laminated Glass

Warm-bent laminated glass is obtained by elastically curving glass plies against a constraining negative mould and by performing, in this condition, the lamination process in autoclave. After removing the constraints, the laminate holds its curved geometry because of the shear coupling from the polymeric interlayer. So curved panels are called “warm bent” to distinguish them from “cold-bent” ones, where flat glass is bent on site and restrained by a frame. An analytical study is presented to describe how, after removal of the constraints, the laminate maintains the curvature only partially, suffering an initial spring-back followed by a long-term relaxation. The model problem considered here is that of two Euler-Bernoulli beams coupled by a thin viscoelastic adhesive layer. Within a variational approach, we analytically describe the relationship between the initial constrained shape and the shape of the curved beam, which is time-dependent due to viscosity of the interlayer. Localized contacts and stress concentrations may occur, depending upon the type of profile that is initially imposed. Comparison of the cases of instantaneous or gradual release of the contact with the mould evidences a remarkable reduction of the transient state of stress in the second case.