Effect of electrical stress on sound propagation of polymeric insulating materials

The application of ultrasonic nondestructive test techniques to detect the degradation of the insulating materials has been investigated. Using the accelerating test, samples of polyvinylchloride, polyethylene, and acrylic were put under electrical stress with different stress levels and different durations. Using the echo-pulse method, ultrasonic velocity was measured for every specimen, before and after the electrical stress. A change in the ultrasonic velocity inside the insulating material was observed after applying the electrical stress. These observations indicate that ultrasonic velocity measurements could be used to detect the degradation as well as the density of the insulating materials