Polymers are widely used in various industries because of their characteristics such as elasticity, abrasion resistance, fatigue resistance and low temperature. In particular, the tensile characteristic of rubber composites is important for the stability of industrial equipment because it determines the energy absorption rates and vibration damping. However, when a product is used for a long period of time, polymers become hardened owing to the changes in characteristics because of aging, thereby reducing the performance and increasing the possibility of accidents. Therefore, accurately predicting the mechanical properties of polymers is important for preventing industrial accidents while operating a machine. In general reactions, the linear Arrhenius equation is used to predict the aging characteristics; however, for rubber composites, it is more accurate to predict the aging characteristics using nonlinear equations rather than linear equations. However, the reason that the characteristic equation of the polymer appears nonlinear is not well known, and studies on the change in the characteristics of the natural and butadiene rubber owing to degradation are still lacking. In this study, a tensile test is performed with different aging temperatures and aging time to evaluate the aging characteristics of rubber composites using strain energy density. We propose a block effect of crosslink structure to express the nonlinear aging characteristics, assuming that a limited reaction can occur owing to the blocking of reactants in the rubber composites. Consequently, we found that a relationship exists between the crosslink structure and aging characteristics when the reduction in crosslink space owing to aging is represented stochastically. In addition, a modified Arrhenius equation, which is expressed as a function of time, is proposed to predict the degradation rate for all aging temperatures and aging times, and the formula is validated by comparing the degradation rate obtained experimentally with the degradation rate predicted by the modified Arrhenius equation.
The correlation between tribological properties of resin bonded copper-graphite composites and electrical signal transmission is investigated. Particular attention is given to the loss of electrical signal at the sliding interface and the amount of signal noise as a function of the composition in the composite. A custom designed slip-ring type tribotester with a copper ring has been used for this study. Results show that the tribological properties of the sliding couple, that is closely associated with morphology of sliding surfaces and the presence of transfer films, determine the amount of voltage drop at the interface and electrical signal noise. The change of the applied load during sliding experiment changes the coefficient of friction (COF) and energy loss at the sliding interface, suggesting that the effective contact area at the rubbing surface of the composite strongly affects the amount of voltage drop. It is also found that the electrical signal noise is directly related with the fluctuation of the friction coefficient caused by the variation of contacts at the sliding interface and by the transient patches of transfer films on the surface of the ring.
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