Ultrasonic Monitoring of Hardness of Industrial Rubbers

Abstract

Ultrasonic testing is normally known to be a very useful Non-Destructive Testing (NDT) method for detecting defects in materials. In recent years, NDT methods are very much in practice and act as a powerful technique for inspecting and measuring various properties of engineering materials. This paper is based on the interaction between characteristics of ultrasonic waves and rubber hardness. An Ultrasonic NDT set-up was developed in-house for recording digitized ultrasonic data in real time. A transmitting as well as receiving transducer with a central frequency of 1 MHz was used during the experiments to generate and capture longitudinal pulse for both natural and synthetic rubbers, having different shore hardness ranging from 55 to 85. It was found that the ultrasonic velocity was not only sensitive to hardness of rubbers, but also to temperatures. The set-up was specially furnished with temperature controllers for calculating ultrasonic velocity in rubber samples at different temperatures. Dependence of ultrasonic wave velocities with hardness and temperatures were studied from experimental observations. Acoustic impedance, reflection, and transmission coefficients were also calculated for explaining the behavior of ultrasonic waves in normal mode.