## 2 Material Testing  
The material employed to construct the prototype PBs is a specially prepared flexible polyurethane-based elastomer. The chemical composition of this polymer includes certain additives to improve its damping properties, which are extremely desirable for energy-dissipation devices, particularly for seismic isolation bearings. The analyzed polymer has been used so far for the crack injections in the recently proposed Flexible Joint Method (FJM), which is an innovative technique of repairing damaged masonry and concrete structures. The effectiveness of the FJM in strengthening damaged structures has been confirmed through many in situ and laboratory tests, and the results obtained from both experimental and numerical studies have been already published (see [35]). In order to get an insight into the basic mechanical characteristics of the analyzed polymer, an extensive material testing was firstly performed. The first stage was to conduct static tension and compression tests with the use of the polymeric cylindrical specimens measuring 28 mm in diameter and 28 mm high. For the purpose of this investigation, a Zwick/Roell Z020 mechanical tester (Zwick/Roell, Ulm, Germany) was employed. The measurements were performed in a room temperature of T = 23 \({}^{\circ}\)C, and relative humidity of 50% for five different strain rates: \(v_{1}=10^{-1}\)s\({}^{-1}\), \(v_{2}=5\times 10^{-2}\)s\({}^{-1}\), \(v_{3}=10^{-2}\)s\({}^{-1}\), \(v_{4}=5\times 10^{-3}\)s\({}^{-1}\), and \(v_{5}=10^{-3}\)s\({}^{-1}\). The tests were conducted until the total failure of the tested specimens. The average stress-strain curves from the static tension and compression tests are shown in Figure 1.  
The results clearly demonstrate that the analyzed polymer is markedly nonlinear and its mechanical behaviour strongly depends on the strain rate, which is typical for viscoelastic materials. If the load is applied slowly, the stress relaxation occurs. On the other hand, if the load arises rapidly, the influence of relaxation phenomena on stress-strain behaviour is less significant. The strength of the tested material, which is a consequence of its modulus, appears to increase with the higher strain rate. Therefore, the higher the strain rate, the larger the force needed to obtain the same deformation level. Figure 1: (**a**) Tensile and (**b**) compressive stress–strain curves for five different deformation rates. In order to determine the dynamic properties of the analyzed polymer, Dynamic Mechanical Analysis (DMA) tests were performed. The DMA test is the most commonly adopted method to measure the viscoelastic parameters of various materials, as they are subjected to constant oscillating deformations over a wide range of temperatures. More specifically, when a sinusoidal load is applied, the resultant sinusoidal strain is measured. In this approach, phase difference between the stress and strain plots, together with the amplitudes of the stress and strain waves, are used to determine a variety of fundamental material parameters, including storage modulus, loss modulus, loss factor, and the glass transition temperature. The storage modulus represents the elastic behaviour of the material and defines the energy stored due to the applied strain. The loss modulus depicts the viscous behaviour of the material and defines its energy dissipation properties. The ratio of the loss to storage modulus, which can be calculated as the tangent of the phase angle between the stress and strain waves, is termed as the loss factor and provides the information on the relationship between the elastic and inelastic components. In addition, the loss factor is frequently used to characterize the damping properties of viscoelastic materials. The larger the tangent of the phase angle, the greater the energy dissipation ability of the material. Finally, the glass transition temperature, which is measured by the peak value of the tangent of the phase angle, separates two dramatically different states of deformation resistance.