Development of a Virtual Instrument for Immersion Type Ultrasonic Inspection with a Computer Controlled Multi-Axis Motion Controller
The Pulse Echo (PE) technique is a widely used ultrasonic non destructive testing technique to test materials by analyzing ultrasound echoes reflected from flaws and discontinuities. In conventional PE technique, called contact type PE, an ultrasonic transducer is in constant contact with a test piece, transmitting and receiving ultrasonic signals from the test specimen. The inherent shortcomings of PE are the need for; uniform couplant conditions, the ultrasonic transducer to remain in contact with the test object throughout the scan and a limitation to scan regular surfaced objects only. This paper provides for extending a system initially developed for contact type PE, to perform Immersion Testing (IT) which is a contactless pulse-echo inspection method with the probe and test piece separated by a predetermined volume of water of certain thickness. A computer controlled 3-axis transducer position manipulator (motion frame) is constructed for assistance in conducting automated tests. The efficacy of immersion testing relies on the precise control of the motion of transducer. The existing immersion type motion controllers along with dedicated data acquisition and analysis system are quite expensive and are beyond the affordability of smaller ultrasonic labs. Hence the proposed system including the motion frame and Data Acquisition Unit (DAQ) can serve as a competent, low-cost and reliable IT system benefitting several small scale industries and labs.
A Study of the Couplant Effects on Contact Ultrasonic Testing
The amplitude of a back-wall echo depends on the reflection coefficient of the interface between a transducer and a test material when using contact pulse-echo ultrasonic testing. A couplant is used to transmit ultrasonic energy across the interface, but has an influence on the amplitude of the pulse-echo signal. To investigate the couplant effect on pulse-echo ultrasonic testing, back-wall echoes are measured by using various couplants made of water and glycerine in a carbon and austenitic stainless steel specimens. The amplitude of the first back-wall echo and the apparent attenuation coefficient increases with the acoustic impedance of the couplant. The couplant having a higher value of the transmission coefficient is more effective for flaw detection. The reflection coefficient should be known in order to measure the attenuation coefficient of the test material.
A review of artificial intelligence applied to ultrasonic defect evaluation
The main objective in ultrasonic defect evaluation is to locate and classify suspect flaw indications quickly and accurately. Since the volume of data to be assessed can be very large, traditional forms of defect evaluation involving a skilled human interpreter are often unsuitable. The progress in the automated evaluation of ultrasonic data has been considerable in recent years and this paper outlines some of the approaches adopted in this area. Traditional pattern recognition techniques and the currently popular neural network approaches have been widely employed to process feature sets, extracted from A-scan signals. Knowledge-based system techniques, although not so widespread, are also considered. A number of authors have taken the approach that such AI techniques should be embedded in an integrated software framework for defect evaluation, and this is also discussed