Research on Out-of-Plane Bending Test of PVB Laminated Glass Plate with Different Number of Layers

Abstract

Polyvinyl Butyral (PVB) laminated glass (LG) with varying numbers of layers is extensively utilized in building structures, and its complex mechanical properties, due to the presence of PVB, pose significant challenges. While comprehensive research has been conducted on the bending behavior of two-layer PVB laminated glass, studies focusing on three-layer variants remain limited. This study aims to investigate the bending behavior of three-layer PVB laminated glass under out-of-plane forces and to ascertain the effects of increasing the number of layers. Experimental studies were carried out on one-, two-, and three-layer PVB laminated glass plates subjected to such loads. During the loading process, the out-of-plane displacement and surface strain of the glass plates were monitored and analyzed. From these observations, load-deflection curves were constructed, allowing for the determination of deflection and strain distribution across the planes. The impact of the number of glass layers on stiffness and ultimate load capacity was examined. Additionally, another experiment was conducted to analyze the mechanical properties of the laminated material (PVB). The research results indicate that the tensile strain at the bottom layer of the laminated glass plate reaches its threshold under an out-of-plane load, leading to a brittle fracture in that layer. However, the remaining layers of PVB LG do not fail at this stage, enabling the plate to continue bearing the load. The average ultimate loads for three-layer, two-layer, and one-layer PVB laminated glass are 37.8 kN, 36 kN, and 24.7 kN, respectively, with a ratio of 1:0.95:0.65. The bending stiffness values for these are 2.77 kN/mm, 1.71 kN/mm, and 1.21 kN/mm, respectively, corresponding to a ratio of 1:0.62:0.44. The stiffness shows a nonlinear increase with the layer count, an effect attributed to the PVB’s characteristics according to the analytical findings. The tensile behavior of the laminated materials demonstrates a bilinear characteristic when subjected to strain. The out-of-plane bending tests on glass plates reveal that when the strain rate is low, PVB behaves like a quasi-linear elastic material. Therefore, for design calculations of PVB LG, adopting an elastic modulus of 1.34 MPa for PVB is deemed reasonable. The findings of this study provide insights for research on laminated glass plates, which are instrumental in refining the calculation methods specified in relevant design standards. Concurrently, it offers guidance for selecting the appropriate number of PVB LG layers in engineering applications.