Cold-lamination-bending of glass: Sinusoidal is better than circular

Cold-lamination-bending (CLB) of glass consists, first, in constraining the unbonded glass-interlayer package in the desired curved shape and, second, in performing the lamination process in autoclave. Releasing the laminate, the curvature is only partially maintained through the interlayer bond, due to an initial spring-back followed by the relaxation of the polymeric interlayer. Here, the whole process of single-curvature CLB, including the phase of release and the consequent contact problem with the constraining mould, is analyzed using sandwich beam theory. Comparisons are made between “stiff” interlayers (like Ionoplastic Polymers) and “soft” interlayers (like PVB). The time-dependent redistribution of stresses due to the interlayer viscosity is found for any assigned initial shape of the mould. Remarkably, the constant-curvature shape, indeed the most used, provokes shear stress concentrations in the interlayer with consequent risks of delamination. The sinusoidal shape, which for typical values of the deformation inappreciably differs from the circular one, provides a much smoother distribution of the shear stresses. A properly-designed gradual release of the laminated glass from the mould can substantially contribute to mitigate the peak stresses.