Investigation of rubber formulation by measuring ultrasonic propagation velocity

Non-destructive tests can identify and investigate the defects and properties of the test piece without changing the physical and mechanical properties of the sample. In this study, the non-destructive inspection method of ultrasonic waves was used to investigate the rubber formulation. In this method, the time between the transmission and the reflection of ultrasonic waves is measured and using this time propagation velocity is calculated. As components percent of the rubber are changed the physical and mechanical properties of rubber are altered and as a result, the velocity of ultrasonic propagation is changed. To investigate the rubber formulation at first 12 samples with different formulations were prepared and for each of the samples the propagation velocity of the longitudinal sound waves was measured. In order to establish the mathematical model between used elements percent in the rubber formulation and longitudinal wave velocity the multiple linear regression was used. To evaluate the accuracy another sample with a new formulation was developed and longitudinal wave velocity was measured. The comparison between the results of the test and those of the regression model showed a low error in the predicted result by the proposed model; therefor, the ultrasonic waves can be used to investigate the rubber formulation and the rubber production lines can use this non-destructive test to control tire quality online.