Dry interlayers out of cast polyurethane rubber for interlocking cast glass structures: experimental exploration and validation

A novel, reversible structural system comprising interlocking, dry-assembled cast glass components is currently being developed at the TU Delft Glass & Transparency Lab. This paper, in continuation of the research conducted by (Oikonomopoulou et al. 2018a), investigates the mechanical properties of different materials that function as dry interlayers for interlocking cast glass structures. The interlayers should be preferably transparent, able to be pre-formed to the desired shapes, and resistant to UV-radiation-induced colour shifts, long-term compressive loads and creep. Based on the above criteria, polyurethane (PU) rubber with a shore hardness between 60A - 80A is chosen as the most suitable material. Accordingly, different readily available PU interlayers are selected and cast in the desired shape. Each interlayer is introduced between two interlocking osteomorphic cast glass components (bricks) and the assembly is tested under compression in series of 3 specimens. The experiments indicate that for the harder interlayer variants, failure mainly occurs due to peak stresses occurring at the shortest section of the brick, where the manufacturing tolerances of the concave-convex surface are the highest, leading to mismatch, i.e. incomplete contact at that area of the interlayer with the glass units. The stiffer interlayers further contribute to the failure due to the increased shear stresses induced at the edges of the interlocking surface while they are deforming. This is evident by the radial breaking pattern of the failed glass blocks. Interlayer variants with low tear resistance fail due to the perforation of the interlayer leading to glass-to-glass contact. Still, all specimens with interlayer in between presented a considerably higher failure stress than an assembly with no interlayer, highlighting the critical contribution of the PU to the structural performance of the system