Prediction of the optimal vulcanization of a fiber-reinforced elastomeric isolator made of natural rubber-ethylene propylene diene monomer blend

To seismically isolate a structure, it is possible to interpose a rubber device between the foundation and superstructure that increases the period of the superstructure, a feature that allows the structure to be “transparent” to the seismic excitation. A package of several rubber pads typically constitutes a seismic isolator; they are 10–20 mm thick vertically interspersed with either steel laminas or fiber-reinforced polymer dry textiles suitably treated. So, the rubber has a primary role and must be vulcanized correctly to create the polymer cross-linking properly. All rubber mechanical properties are strongly affected by curing temperature and curing time. Under vulcanization is a typical production error that suppliers make in large-scale productions, especially when the size of the devices is considerable. It is common to deal with elastomeric isolators where rubber pads have been treated at a largely suboptimal temperature. This article proposes a numerical model for predicting the cross-linking degree of rubber pads used in seismic isolation and made by a natural rubber-ethylene propylene diene monomer rubber compound. The aim is to correctly define the optimal curing temperature and exposition time for producing a rubber quadruple shear test specimen and a fiber reinforced elastomeric isolator (FREI). The model is a kinetic one and takes into consideration the induction time. An experimental investigation has been conducted to validate the model with visible inspections and hardness measurements taken on the rubber pads (quadruple shear specimens) and the rubber devices. The results have shown the reliability of the new numerical model proposed, with a homogeneous mechanical properties distribution obtained within the rubber pads and the FREI.