Određivanje rezolucije pomaka i deformacija metodom korelacije digitalnih volumena na epoksidnoj smoli ojačanoj staklenim vlaknima

undergraduate thesis

• Title (english): Evaluation of displacement and strain resolution of digital volume correlation algorithm applied on glass fiber reinforced epoxy resin
• Author: Gabrijel Mađerić
• Mentor: Zvonimir Tomičević (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2019-03-01, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering

Abstract

Jedna od najčešće korištenih suvremenih metoda za nerazorna ispitivanja kompozitnih materijala je računalna tomografija (CT). S obzirom na sve veću primjenu kompozita u svim granama industrije potrebna su sve naprednija ispitivanja koja vrlo precizno mogu procijeniti odziv materijala uslijed mehaničkog opterećenja. Računalna tomografija radiološka je metoda koja koristi snop ionizirajućeg zračenja kako bi se mogla odrediti vanjska i unutarnja struktura mjernog objekta. Osim toga, pomoću ove metode mjerenja dostupne su informacije o geometriji ispitnog uzorka i mikrostrukturi promatranog objekta. Kod mjerenja CT uređajem javljaju se različiti šumovi i mjerne nesigurnosti, uzrokovane vanjskim i unutarnjim čimbenicima, koje direktno utječu na kvalitetu dobivenih 3D volumena.
S obzirom da su zabilježeni 3D skenovi niz digitalno zapisanih slika, na rekonstruiranim volumenima moguće je provesti mjerenja cijelog polja pomaka i deformacija primjenom korelacije digitalnih volumena (DVC) čiji se algoritam temelji na metodi korelacije digitalne slike. Osim mjerenja na površini ispitnog uzorka DVC metoda nam dozvoljava pristup odziva materijala unutar ispitnog uzorka.

U ovom radu provedeno je skeniranje uzorka za vlačno ispitivanje. Skeniranje je provedeno pomoću industrijskog μ-tomografa NIKON XT H 225. Uzorak za vlačno ispitivanje kompozitni je materijal izrađen od mat staklenih vlakana koja se nalaze u matrici od epoksidne smole. Skeniranje je provedeno uzastopno dva puta kada je uzorak bio u neopterećenom stanju. Provedenom rekonstrukcijom registriranih projekcija definiran je 3D volumen na kojem je zatim primijenjena DVC metoda s ciljem određivanja polja pomaka odnosno deformacija unutar ispitnog uzorka. U ovom radu korišten je globalni DVC algoritam Correli C8 koji se zasniva na metodi konačnih elemenata. Iz izmjerenih podataka promatrano je kako šumovi i mjerne nesigurnosti utječu na veličinu konačnih elemenata korištenih kod mjerenja pomaka i deformacija. Glavni cilj ovog rada je određivanje standardne rezolucija pomaka i deformacija za različite veličine konačnih elemenata. Izmjerene vrijednosti standardne rezolucija pomaka i deformacija analizirane kod neopterećenog ispitnog uzorka važne su za daljnja mehanička ispitivanja. Poznavanjem standardne rezolucije pomaka i deformacija definiran je najmanji prirast pomaka odnosno deformacija koje se može mjeriti ovom tehnikom s obzirom na primijenjenu veličinu konačnog elementa.

Abstract (english)

Computed tomography (CT) is one of the most commonly used modern methods for non-destructive testing of composite materials. Considering increased application of composite materials in many industries, more advanced tests are required to accurately estimate material behaviour due to mehanical loading. Computed tomography is a radiological method that uses the beam of ionizing radiation to determine external and internal structure of the measuring object. Moreover, informations about the geometry and the microstructure of the observed object are available when proposed measurement method is applied. Various noise and uncertainities, caused by different external and internal factors, are generated while acquiring radiographs with the CT device which can directly affects the quality of the obtained 3D volumes.
Since registered 3D scans are series of digitally recorded images, measurement of the entire displacement and strain fields can be performed on the reconstrucetd volumes applying the Digital Volume Correlation (DVC), based on the already established Digital Image Correlation (DIC). However, in addition to measurements on the surface of the test sample, the DVC method allows us to access the material response within the test sample.

Within this work the 3D volume of the uniaxial dog bone sample was conducted. The device used for this test was industrial μ-tomograph NIKON XT H 225. The dog bone sample was made of the mat glass fibers embedded in epoxy resin. The acquisition of the 3D scans was performed two times consecutively when the sample was in unloaded state. 3D volume was then recontructed from the recorded 2D projections. Afterwards, the DVC method was applied to measure displacement and strain fields within the dog bone specimen. In this work, global DVC algorithm Correli C8, based on the finite element method, was used. The aim was to observe the influence of the noise and uncertanities on finite element size, for measuring displacements and strains, was then observed from measured data.

The objective of this work is to determine the standard displacement and strain resolution for different size of C8 finite elements. Registered values of the standard displacement and strain resolution, analyzed in the unloaded sample, are very important for further mechanical testing via μ-tomography. The smallest increase of the displacement and strain values, considering the applied finite element size, that can be measured with the proposed technique are defined by accessing the standard displacement and strain resolution.

• Keywords: kompozit; nerazorna ispitivanja; računalna tomografija X-zrakama (X-CT); korelacija digitalnog volumena; standardna rezolucija pomaka; standardna rezolucija deformacija
• Keywords (english): composite material; non-destructive testing; X-ray computed tomography (X-CT); Digital Volume Correlation (DVC); standard displacement resolution; standard strain resolution
• Language: croatian
• URN:NBN: urn:nbn:hr:235:559531
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: undergraduate; Academic / professional title: sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka strojarstva (sveučilišni/a prvostupnik/ prvostupnica (baccalaureus/baccalaurea) inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2019-05-23 00:21:31