An Evaluation Approach to NDT Ultrasound Processes by Wavelet Transform

摘要

The possibility of employing wavelet analysis in ultrasonic nondestructivernapplications has been studied since the beginning of the eighties, givingrninteresting results at least in laboratory applications. Nevertheless, inrnorder to apply this technique efficiently as an analysis tool supporting therndiagnosis process in routinely Quality Control applications, it is necessaryrnto further assess the applicability conditions. To this purpose, within thernframe of the European IMT Research Program INDUCE, an evaluation andrndevelopment activity is running, focused on some nowadays productionrncritical diagnosis targets. This paper reports the preliminary resultsrnobtained. In particular, one-dimensional signals (pulse-echo waveforms) wererninvestigated; features from scale-time plots were studied; a prototype ofrngraphic interface for the control of the processing of two-dimensionalrnsignals and programs for file management and data processing were developed;rnoperating correlation with a global NDT data organisation model wasrnestablished. Some flaws (delamination, bridging, insert) in carbon fibrerncomposite components were investigated, with special reference to therndiscrimination between micro-voids and resin enrichment zones and to somerncritical time-position of flaw peaks (e.g. small void signal near the frontechornone). Moreover, taking into account the impracticability of collectingrna sufficiently high number of experimental representative situations, arnsemi-empirical modelling was formulated, in order to provide knownrndefect/structure/flaw-location configurations able to address waveletrntransform applications. MATLAB Tools were used. Results encourage deeperrninvestigation, aiming particularly at the possibility to automate some flawextractionrnalgorithms, both in terms of detection and characterisation.