A Comparative Study of Ultrasonic Contact and Immersion Method for Dimensional Measurements

Ultrasonic testing (UT) is one of the most widely used techniques for non-destructive testing. This is an effective method to provide information of the test material like dimension, geometry, and shape. The precise thickness measurement is necessary for many industries to observe the deterioration, destruction and damages in metals, composite structures, pipes, soldering, and welding. In UT, the pulse-echo (PE) method is the conventional ultrasonic method used for testing and acquiring information about the specimen. In PE method, the ultrasonic wave is transmitted by the single transducer and the reflected signal from the specimen is received back by the same transducer. The duration between transmitted and received signal, e.g., time of flight is then measured. In this article, a comparative study of the dimensional measurements (thickness measurements) of an ASTM (American Society for Testing and Materials) reference block is carried out using ultrasonic contact and immersion methods. Longitudinal ultrasound was generated in the reference block by a piezoelectric broadband transducer. The responses of the ultrasonic echoes were recorded using an ultrasonic flaw detector. For the ultrasonic testing, the uncertainty associated with thickness measurement of a standard ASTM reference block is found as ± 0.035 mm while using immersion method. However, the estimated uncertainty is higher as ± 0.088 mm in case of contact method. The study clearly shows that the immersion testing system is capable to precisely measure the thickness with relatively lower uncertainty than the contact approach.