Lap shear tests on adhesive bonds of historic iron and mild steel

Putty has been used for ages to seal the connection between glass plates and glazing bars in window frames or iron and glass roofs. Nowadays, putty can be replaced by adhesive, to make the two materials structurally work together. To gain insight in the structural behaviour, this article examines the magnitude of the stresses that can be transmitted between glass panels and historic iron which are bonded with modern adhesive.
Experiments on single-lap joints were carried out to determine the influence of parameters, specific for renovation, on the shear strength. The material of the substrate (modern construction steel/19th century mild steel), its surface roughness (obtained by grit blasting) and its treatment (application of zinc-phosphate epoxy paint) were tested. All substrates were bonded with an MS polymer adhesive. The experiments demonstrated that a variation in surface roughness has a small effect on the average shear strength, which is positive for the renovation practice. However, the time period between grit blasting and bonding/applying a paint layer seemed crucial.