Analysis of glass/polyvinyl butyral laminates subjected to uniform pressure

Complex stress fields develop during the loading of glass/polymer laminates used as architectural safety glazing due to: (1) large glass/polymer modul us mismatch (E-glass/E-polymer similar to 10(3)-10(5)), (2) polymer viscoel asticity, and (3) nonlinear, large deflection behavior encountered in comme rcial scale glazing. We present a model for stress analysis of such laminat es that consists of a three-dimensional finite-element model incorporating polymer viscoelasticity and large deformations. The model has been applied to study quasi-static deformation of a square, simply supported, glass/poly vinyl butyral/glass laminate in response to uniform pressure loading. One o f the major findings is that stress development may fall outside the so-cal led "monolithic" limit, for two well-bonded pieces of glass, and the "layer ed" limit, for two freely sliding plates. One reason is because deformation of large plates prior to glass first cracking includes considerable membra ne stresses and the monolithic and layered limits are derived for the case of small bending deflections of beams. We also find that stress development is influenced by temperature (or loading rate), particularly in the vicini ty of the polymer glass transition temperature. However, the effect of temp erature can be diminished at large deflections as membrane stresses dominat e and coupling between glass plies plays a lesser role in stress developmen t. A method is presented to compute the probability of glass first cracking by combining our finite-element-based stress analysis with a Weibull stati stical description of glass fracture. One surprising result of the analysis is that for typical glass Weibull moduli (5-10), the Weibull effective str ess used to compute the probability of first cracking is only weakly depend ent on temperature. The stress analysis and failure prediction model presen ted may be applied to describe the load-bearing capacity of laminates of ar bitrary shape and size under specified loading and support conditions.