An evaluation approach to NDT ultrasound processes by wavelet transform

The possibility of employing wavelet analysis in ultrasonic nondestructive applications has been studied since the beginning of the eighties, giving interesting results at least in laboratory applications. Nevertheless, in order to apply this technique efficiently as an analysis tool supporting the diagnosis process in routinely Quality Control applications, it is necessary to further assess the applicability conditions. To this purpose, within the frame of the European IMT Research Program INDUCE, an evaluation and development activity is running, focused on some nowadays production critical diagnosis targets. This paper reports the preliminary results obtained. In particular, one-dimensional signals (pulse-echo waveforms) were investigated; features from scale-time plots were studied; a prototype of graphic interface for the control of the processing of two-dimensional signals and programs for file management and data processing were developed; operating correlation with a global NDT data organization model was established. Some flaws (delamination, bridging, insert) in carbon fibre composite components were investigated, with special reference to the discrimination between micro-voids and resin enrichment zones and to some critical time-position of flaw peaks (e.g. small void signal near the front-echo one). Moreover, taking into account the impracticability of collecting a sufficiently high number of experimental representative situations, a semi-empirical modelling was formulated, in order to provide known defect/structure/flaw-location configurations able to address wavelet transform applications. MATLAB Tools were used. Results encourage deeper investigation, aiming particularly at the possibility to automate some flaw-extraction algorithms, both in terms of detection and characterization.