Nonlinearity based signal processing for defect detection

Koen Van Den Abeele, Jan Hettler, Seyed Morteza Tabatabaeipour, Steven Delrue

Research output: Contribution to conferenceAbstractpeer-review


When seeking out evidence for nonlinear behaviour, various signal processing techniques can be applied for the comparison of two signals, one being a slight distortion of the other. For instance, the pulse inversion technique compares the responses to two out-of-phase excitation signals. Alternatively, one can compare the response at a finite (nonlinear) excitation amplitude to a scaled response at a very low (linear) excitation, as performed in the scaling subtraction technique. In this report, several numerical as well as experimental examples are given in which these nonlinearity based signal processing techniques are used in practice to visualize damage features in solids. In view of kissing bond defect detection in friction stir welds, the pulse-inversion method was employed in a contact pitch-catch mode using a chirp signal. B-scan spectral heat maps obtained after pulse inversion allow to easily identify and size damage zones along the weld path. Secondly, the scale subtraction technique will be illustrated in combination with an ultrasonic sparse array SHM system to detect damage locations (impacts and delaminations in CFRP plates) without the need of baseline signals taken on an intact specimen. Finally, we show that the phenomenon of Local Defect Resonance (LDR) can be facilitated and validated using the scaling subtraction technique.
Original languageEnglish
Publication statusPublished (in print/issue) - 12 Jun 2017
EventNew Mathematics for a Safer World: Wave Propagation in Heterogeneous Materials - 15 South College Street, Edinburgh, United Kingdom
Duration: 12 Jun 201715 Jun 2017
Conference number: 2017


ConferenceNew Mathematics for a Safer World: Wave Propagation in Heterogeneous Materials
Abbreviated titleICMS
Country/TerritoryUnited Kingdom
OtherThere are safety critical structures all around us such as nuclear plants, aircraft, gas pipelines, bridges and railway tracks. They are safety critical since any failure is potentially catastrophic. To avoid such disasters these structures are checked periodically for the presence of flaws and other precursors to the component failing. This is performed at various stages in the lifetime of the component: at the manufacturing stage, while the component is in service, and to assess the component for re-manufacturing at the end of its lifetime. Safety has become more pressing of late as many of these structures are operating well beyond their intended lifespan. To address this problem there have been rapid developments in the types of ultrasonic sensors that are used to find these flaws and cracks. These sensors produce massive data sets and therefore require a matched development in the mathematical algorithms used to extract the knowledge from this data. To enable this development this workshop brought together leading mathematicians, engineers and those from other disciplines.
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  • ultrasonic
  • nonlinearity
  • NDT
  • composite
  • welding


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