Spatial localization of air inclusions in carbon fiber T-beam, by use of wavelet entropy time series from hammer tap test.

Σπυρίδων, Μπρούζας; Spyridon, Brouzas

dc.contributor.author	Σπυρίδων, Μπρούζας	el
dc.contributor.author	Spyridon, Brouzas	en
dc.date.accessioned	2021-09-07T09:52:02Z
dc.date.available	2021-09-07T09:52:02Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/53809
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.21507
dc.rights	Αναφορά Δημιουργού 3.0 Ελλάδα	*
dc.rights.uri	http://creativecommons.org/licenses/by/3.0/gr/	*
dc.subject	NDT	en
dc.subject	Wavelet entropy time series	en
dc.subject	Carbon fiber	en
dc.title	Spatial localization of air inclusions in carbon fiber T-beam, by use of wavelet entropy time series from hammer tap test.	en
heal.type	bachelorThesis
heal.classification	engineering	en
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2021-05-21
heal.abstract	Many critical safety structures such as aircrafts are constructed using extensively composite materials; therefore, non-destructive testing (NDT) of composite structures is imperative. The following thesis investigates a new method of NDT for carbon fi ber structures based on the analysis of a vibration signal after exciting the composite specimen with a pulse. The analysis proposed in this report consists of transforming the signal using the Haar Wavelet Transform, segmenting the Transform in the time domain and calculating its Informational Entropy, as de fined by Shannon, for every frame (Wavelet Entropy Time Series). The use of Wavelet Transform in combination with Shannons Informational Entropy (Wavelet Entropy) has been proven to identify irregularities in signals, mostly when comparing them to healthy signals using the Kullback Leibler Divergence (Relative Wavelet Entropy). Wavelet Entropy Time Series requires no additional signals for comparison. In this thesis, notions such as Wavelet Entropy and Wavelet Entropy Time Series are introduced and defi ned. The presupposition that Wavelet Entropy Time Series can single out and localize damaged areas of a structure is backed up both theoretically and experimentally. To prove this experimentally, a carbon-fi ber T-beam containing air inclusions was subject to hammer tap tests across its length. Accelerometers were mounted along its long axis. For every excitation, these accelerometers measured the vibration signals, which were then analyzed using Wavelet Entropy Time Series, and viewing its trend. The experiment identifi ed 2 locations where the Wavelet Entropy Time Series follows an increasing path. The signal from exciting the adjacent area to these locations also exhibits similar behavior those locations but with less intensity. Repetition of the experiment provides similar results proving that the outcomes were not random. It is therefore clear that the properties of the beam locally differ from the rest of the beam. This in combination with the knowledge that the beam contains air inclusions gives us a strong indication for their existence. However, extensive research is required to establish the accuracy and applicability of this NDT method. Non-destructive testing (NDT) of composite specimens can be a tedious task, as such, any new NDT method can be a new tool in the arsenal of an NDT inspector. The applicability of wavelet entropy time series for NDT could also probably extend outside of composite materials, for example in metal structures. The method, should it be developed commercially, could be a low-cost, reliable testing technique that requires just a computer, an accelerometer with relatively small sampling frequency of 5000Hz as well as little to no specialization on behalf of the tester.	en
heal.advisorName	Γεωργίου, Ιοάννης	el
heal.committeeMemberName	Σπύρου, Κωσταντίνος	el
heal.committeeMemberName	Μπελιμπασάκης, Κωσταντίνος	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Ναυπηγών Μηχανολόγων Μηχανικών. Τομέας Ναυτικής Μηχανολογίας. Εργαστήριο Ναυτικής Μηχανολογίας	el
heal.academicPublisherID	ntua
heal.numberOfPages	156 σ.	el
heal.fullTextAvailability	false