Analysis of Glass/Polyvinyl Butyral Laminates Subjected to Uniform Pressure

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Abstract
Complex stress fields develop during the loading of glass/polymer laminates used as architectural safety glazing due to: (1) large glass/polymer modulus mismatch (Eglass/Epolymer ∼ 103–105), (2) polymer viscoelasticity, and (3) nonlinear, large deflection behavior encountered in commercial scale glazing. We present a model for stress analysis of such laminates 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/polyvinyl butyral/glass laminate in response to uniform pressure loading. One of the major findings is that stress development may fall outside the so-called “monolithic” limit, for two well-bonded pieces of glass, and the “layered” limit, for two freely sliding plates. One reason is because deformation of large plates prior to glass first cracking includes considerable membrane 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 vicinity of the polymer glass transition temperature. However, the effect of temperature can be diminished at large deflections as membrane stresses dominate and coupling between glass plies plays a lesser role in stress development. A method is presented to compute the probability of glass first cracking by combining our finite-element-based stress analysis with a Weibull statistical description of glass fracture. One surprising result of the analysis is that for typical glass Weibull moduli (5–10), the Weibull effective stress used to compute the probability of first cracking is only weakly dependent on temperature. The stress analysis and failure prediction model presented may be applied to describe the load-bearing capacity of laminates of arbitrary shape and size under specified loading and support conditions.

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