Ultrasound lockin thermography as a quantitative technique for quality control assessment of cast iron turbine components

Abstract

This paper explores the application of ultrasound activated infrared thermography for the detection and quantification of flaws in industrial cast iron turbocharger components. The use of amplitude modulated ultrasonic heat generation allowed selective response of defected area, since the defect itself is turned into a local thermal wave emitter. Due to the very fast cycle time (< 30 s/part), the method could potentially be applied for 100% quality control of cast parts.After a brief description of the measurement technique and experimental setup used to carry out the tests, main results and discussion are reported. Most emphasis has been addressed to assess the influence of different operative parameters on defect's detection capability as well as accurate sizing of the discontinuity.

Investigation of heat generation sources in lock-in sonic thermography using laser Doppler vibrometry

“…In addition, it requires only a relatively low excitation power to heat the defect, thus preventing potential damage of the inspected part caused by high-amplitude vibrations. ULT has been proposed in recent years as an effective NDT method in a number of applications, such as imaging of aerospace structures [7], non-destructive testing of adhesive joints and riveted structures [8], maintenance of CFRP rims [9], qualification of industrial cast iron turbocharger components [10] and cracks detection in steel load bearing members [11]. Acoustic excitation can also be accomplished by using short sonic multi-frequency bursts (UBP) [12] or wideband frequency sweeps (UST) [13] in order to reduce the testing time and eliminate the effects related to the onset of undesirable standing wave patterns caused by ultrasound frequency matching with structural resonances.…”