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Recovery Behaviour of Laminated Cold Bent Glass: Numerical Analysis and Testing

Speaker: Sophie Pennetier, Project Engineer, SHoP Construction
Series: MMS Brown Bag Seminars
Location: Engineering Quad E219
Date/Time: Thursday, August 29, 2013, 12:30 p.m. - 2:00 p.m.

Abstract:

The behaviour of laminated glass largely depends on the mechanical properties of the interlayer. For linear, static calculation, simplified representations of laminates usually give satisfactory, reliable results. In contrast, if more refined membrane or time dependent behaviour shall be taken into account, the comprehension of the interlayer properties is fundamental, since most interlayers such as PVB or SG present a strong nonlinear viscoelastic behaviour comprising shear modulus depending on time, loading and temperature.

In particular, integration of interlayer properties allows studying complex products such as the recent technology of laminated cold bent glass, where glass panels are elastically bent into a curved shape and then laminated for establishing a shear-compound preserving the deformation. Interior stress from this process causes short- and long-term springback behaviour of the laminate if the panel is not held in position. A full understanding of this phenomenon is important for predicting the interior stress and geometrical shape of the glass at different stages. Furthermore, relaxation of the laminates introduces forces in the supporting structure.

The work presented here is based on initial research and testing for getting reliable interlayer and compound properties. A FE-model taking into account the viscoelastic properties of the interlayer has been realised in order to simulate the cold bending procedure as well as the spring back occurring initially (after release from the bending jig) and after several months. The numerical model is done with CODE ASTER software comprising geometrical and material non-linear analysis, e.g. the viscoelastic interlayer material. For comparison, a similar model has been independently realised in ANSYS at the ITKE.

The numerical results need to be validated against physical tests, thus laminated cold bent specimens (2.4 x 0.8m, curvature radius 5m) as a scaled version of those used at Strasbourg railway station being a reference building in this field, have been tested at the University of Stuttgart. 3D-monitoring of the springback as long term effect has been conducted using photogrammetry over a time period greater than three months. Results provide information about the short- and long-term influence of boundary conditions such as material properties, initial bending shape or manufacturing technique.