An Ultrasonic Non-Destructive Evaluation of Contents of Silica Powder and Carbon Black in Nitrile Rubbers

Abstract Ultrasonic testing is primarily used as one of the popular non-destructive methods. Ultrasonic non-destructive methodologies are also being used as effective tools for process characterization and property detection in engineering materials, including polymers, rubbers etc. Different additives are mixed with pure rubber to improve mechanical properties like hardness, tensile strength, ductility etc. Such property changes are seen to have direct bearings on features of ultrasonic waves. The present research is focused on the study of the interaction between ultrasonic wave velocity and quantum of additives (silica powder, carbon black) in rubbers. Nitrile rubber samples, mixed with different weight percentages of silica powder (varying from 28 to 43%) and carbon black (varying from 16 to 43%), have been considered for experimentation. An experimental setup, consisting of an ultrasonic transducer and heating arrangement, has been developed in-house for observing ultrasonic pulse behaviour from the samples at varying temperatures (30–160°C). All the experiments have been carried out with a 1 MHz piezoelectric transducer operating in pulse-echo mode to determine ultrasonic wave velocity in the longitudinal mode in the rubber samples at different temperatures. It is found that the experimental results, that the variation of ultrasonic longitudinal velocity (ULV) in NBR samples at different temperatures are able to differentiate the types of additives and their contents (in wt %) in them by the slope and intercept of the best-fit-line of the ULV vs. temperature variations, respectively.