No abstract

We subjected rubber coupons to cyclical uniaxial tension to investigate the softening effect, where the primary loading at its initial position was followed by additional unloading and reloading. Less stress was required upon reloading than that required in the previous loading for the same degree of stretch, reached on the first loading. This stress softening is significant when reloading follows virgin loading. The magnitude of stress softening is related to the maximum stretch elastomers can achieve in each cycle. To investigate this phenomenon, rubber coupons were subjected to four cycles of simple tension until the desired stretch was reached. We expected that several tests under the same conditions would provide almost identical results. However, we observed different stress requirements for different degrees of stretch when multiple cycles of the same stretch were performed. For three different experimental tests of the same amount of stretch, we saw huge differences in each cycle of loading-relaxation-reloading, a phenomenon that was more obvious during stress relaxation.

This study aims to model and validate the influence of temperature on the stress relaxation of silicone rubber, numerically. The stress relaxation tests were performed at a constant strain level using a constant crosshead speed at the below ambient temperatures. The Time-Temperature superposition, The Williams-Landed-Ferry (WLF), was applied to describe temperature and stress relaxation of Silicone rubber. First, the master curve was obtained, and then the WLF coefficients were determined by curve fitting technique. This study demonstrated that temperature affected the stress relaxation and stress relaxation decreases with decreasing temperature. Also, FEM results validated the experimental results.

This study aims to experimentally compare the elasto-mechanical behaviors of ethylene propylene diene monomer rubber (EPDM), neoprene rubber, silicone rubber, and natural rubber. Rubbers were tested under uniaxial, equibiaxial, and planar loading for five different samples of each material, and the average values have been calculated. Based on the experimental results, a rubber identification was performed by using different rubber models such as Ogden, Mooney-Rivlin, etc. presented in the literature. The result of this study demonstrated that the EPDM rubber showed the highest stress value compared to the other rubbers, silicone rubber, and natural rubber showed similar behavior. Moreover, Neoprene rubber showed the lowest stress value.

Modeling and analysis of a system of two self-balancing pendulums is presented in this paper. Such systems are commonly used as elements of automotive door latch mechanisms that can be subjected to oscillatory excitation or vibratory inertia forces occurring during crash events. In order to avoid an unwanted behavior such as opening of the door, the considered mechanism should be properly designed and its dynamical response well understood and predictable. One pendulum of the double-pendulum system, playing the role of a counterweight (CW), is used to reduce the second (or main) pendulum motion under inertia loading. The interaction force between the pendulums is defined as the reaction of a holonomic constraint linking the rotations of both pendulums. Another reaction force acts between one of the pendulums and the support, reinforced by the action of a preloaded spring. An important aspect of the model is its discontinuous nature due to the presence of a gap in the interface area. This may result in impacts between both pendulums and between one of the pendulums and the support. High-frequency/high-acceleration amplitude vibratory motion of the base part provides inertia input to the system. Classical multibody dynamics approach is adopted first to solve the equations of motion. It is shown that the considered system under certain conditions responds with a high-amplitude irregular motion. A special methodology is used in order to study the regions of chaotic motion, with the goal to gain more understanding of the considered system dynamics. Bifurcation diagrams are presented together with quantitative and qualitative analysis of the motion. The sensitivity of solutions to variation of system parameters and input characteristics is also analyzed in the paper.