## 2 Sample Characteristics  
The isolator prototypes were built by ILPEA Industries of Pordenone, Italy, and experimentally tested at the Laboratory for Testing Materials and Structures of the University of Udine, Italy. The samples were square-shaped and small, because this configuration results in the lowest cost for the manufacturer. The thickness of the elastomer and steel layers were realized in the same order of magnitude of those used for medium-size real isolators. The geometrical characteristics of the samples are shown in Figure 2.  
The samples were produced using a square-based mold, in which a 20 mm thick steel plate was placed at the bottom and an elastomer covering of 5 mm (if provided) was placed on the vertical lateral surfaces. Subsequently, 6 mm thick elastomer layers alternating with the 3 mm thick reinforcement elements, were inserted one on top of the other. The steel reinforcements were sandblasted and pre-treated with primer and mastic. The sandblasting roughens the steel surface to facilitate bonding. The primer, applied directly to the steel, is a chemical substance that is meant to improve the adhesion between steel and mastic. The  
Figure 2: Geometrical characteristics of samples used for the tensile tests. mastic, a liquid glue. is applied over the primer to paste the elastomer layer to the steel reinforcement. After the whole mold is filled with these layers, the next operation is the vulcanization. During vulcanization the layers are subjected, for certain period of time, to a pre-determined compression at a temperature that causes them to glue to each other, so that the layers are held together and substantially constitute a single body. The vulcanization time varies, depending on the dimensions of the isolator. The characteristics of all 24 tested samples are reported in Table 1.  
Elastomer layers with three different shear modulus, G = 0.4 MPa, G = 0.8 MPa and G = 1.4 MPa, were used. Different types of compound can be present in a group of samples with the same shear modulus. The compounds that were considered and their characteristics are:  
* 35,713--hardness 70, shore A, styrene butadiene rubber (SBR)-based, which is a synthetic rubber, dissipative compound
* 35,718--hardness 60, shore A, natural rubber (NR)-based, dissipative compound
* 34,821--hardness 40, shore A, NR-based, dissipative compound
* 312--hardness 70, shore A, SBR-based, non-dissipative compound
* 27,303--hardness 60, shore A, SBR-based, dissipative compound. All of these compounds are used by ILPEA to produce seismic isolators, apart from compound 312, which is used to produce road joints. This compound has good abrasion resistance and good elongation capacity, but it is not dissipative. To investigate how the adhesion between elastomer and steel layers can vary, the following manufacturing processes were taken into consideration:  
* The basic vulcanization time of the tested samples, considering their dimensions is 135 min according to ILPEA manufacturing standards. In the experimental campaign, this time was varied to investigate if the variation produced effects on the layers' adhesion. Longer vulcanization time involves longer pressure application and heating, which are the processes that result in the reorganization of the rubber compound crosslinks to obtain the final elastomer and the gluing of the elastomer to the steel layers. Time periods of 150 and 180 min are taken into consideration. * Corundum was used for sandblasting instead of standard grit to produce some of the samples used in the study. Corundum is an aluminum oxide and it is used in the manufacture of abrasives because of its great hardness, which is close to that of diamond. It can also be produced synthetically. This material may be able to increase the roughness of steel reinforcements, and consequently, the adhesion between steel and elastomer layers. * Isolators usually have an elastomer layer covering the lateral external surface.