Novel perspectives on self-monitoring internal rubber failure using piezoresistivity

Carbon black (CB) fillers are often used to increase the ultimate strength and durability of rubber products. Incidentally, CBs are also electrically conductive and this property at low filler concentrations was successfully exploited by several researchers to monitor changes in mechanical properties of rubber by piezoresistance evaluation. In the present work, piezoresistive response of deformed natural rubber (NR) filled with higher concentrations of CB, which are often encountered in rubber products under dynamic loading conditions like tires, conveyor belts, vibration dampers and the like was investigated. Unfortunately, high carbon black content significantly decreased piezoresistive signal, severely limiting the self-monitoring capability. Moreover, unexpectedly high and undesirable for electromechanical application such as precursor of shoulder peak phenomenon (PSPP) and shoulder peak phenomenon (SPP) were observed. However, these otherwise undesirable phenomena in a noble way was used for self-monitoring the rubber integrity during cyclic deformation. The gradual increase in residual strain, indicating rubber matrix fatigue, was clearly related to changes in experimentally detectable electrical resistance as a function of PSPP and SPP. The study is optimistic of a new concept for self-monitoring and forecasting rubber structure degradation under long-term cyclic loading predictable from simple obtainable piezoresistive response.