Tensile tests for the improvement of adhesion between rubber and steel layers in elastomeric isolators

Steel reinforced elastomeric isolators are currently the most used bearings for seismic isolation purposes. The steel reinforcements are cut to the desired shape, sandblasted, cleaned with acid, and coated with bonding compound during the manufacturing process. Then the elastomer and steel layers are stacked in a mold and subjected to vulcanization so that they are glued together and constitute a single body. Good adhesion between the layers is very important for the correct functioning of the device. Adhesion conditions become critical when the isolators are subjected to tensile stresses, which arise under direct tensile actions or large shear strains. To analyze the influence of changes in the manufacturing process on the isolator adhesive behavior, the authors performed tensile tests on square-shaped small-scale specimens rather than expensive shear tests on full-scale isolators. Hence, the adhesion behavior between elastomer and steel layers was investigated through the tensile tests discussed herein. Among the influencing parameters that were considered, it was found that an increase in vulcanization time does not improve the adhesion, but it may actually worsen the capacity of the isolator in terms of strength. Moreover, it was found that using elastomer without an oily component improves the adhesion between the layers and increases the isolator’s dissipative capacity.