A practical, nondestructive method to determine the shear relaxation modulus behavior of polymeric interlayers for laminated glass

A practical, nondestructive method to determine the shear relaxation modulus behavior of viscoelastic polymer interlayers used in laminated glass is demonstrated. The method is based on a direct measurement of the laminate effective thickness using a four point bend test geometry or uniform pressure loading of laminate plates. The effective thickness expressions that incorporate the polymer shear modulus explicitly in the formulation are then used to calculate the polymer shear modulus in an inverse fashion. Comparison of this approach with dynamic mechanical analysis shows the new approach to be accurate over a wide range of test conditions. The approach described has the advantage of being able to characterize the polymer interlayer in situ. We have focused on laminated glass in this study, but the approach is applicable to any laminated combination of different material types consisting of a compliant core sandwiched between stiff skins.