Mjerenje izvan ravninskih pomaka i deformacija uslijed smičnog opterećenja primjenom stereo korelacije digitalne slike

undergraduate thesis

• Title (english): Measurement of out-of plane displacement and deformation due to shear load using stereo correlation of digital image
• Author: Petra Vinčić
• 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

Određivanje mehaničkih svojstava materijala pri jednostavnom i složenom opterećenju od velike je važnosti budući da je većina inženjerskih konstrukcija tijekom eksploatacije podvrgnuta kompleksnim režimima opterećenja. Cilj eksperimentalnih ispitivanja je identifikacija mehaničkih parametara materijala kako bi se pouzdanije opisalo ponašanje materijala i procijenio životni vijek konstrukcije. Postojeće metode za ispitivanje materijala na smik unazad nekoliko godina se konstantno modificiraju jer se uz smik na ispitnim uzorcima pojavljuje i efekt izvan ravninskog savijanja. Najpoznatije metode mehaničkih smičnih ispitivanja provode se na Iosipescu i Arcan prihvatu. Obje test metode koriste leptiraste ispitne uzorke s dva V zareza (eng. butterfly specimen) kako bi se između njih postiglo ujednačeno stanje smicanja. Osim toga, kako bi se odredilo ponašanje materijala uslijed smičnog opterećenja provode se mehanički eksperimenti uvijanja štapova okruglog ili pravokutnog presjeka.
U ovom radu je provedeno ispitivanje leptirastih uzoraka na jednoosnoj elektromehaničkoj kidalici Beta 50-5 (Messphysik Austrija). Smično opterećenje je na ispitni uzorak preneseno pomoću modificiranog višeosnog Arcan prihvata. Cilj ovog rada je odrediti izvan ravninske pomake i deformacije na uzorcima različitih debljina. Za predložena ispitivanja su korišteni uzorci debljina 1, 2, 3 i 4 mm izrađeni od konstrukcijskog čelika DC01. Polja pomaka i deformacija na površini uzorka izmjerena su metodom korelacije digitalne slike. Za određivanje izvan ravninskih polja pomaka i deformacija korišten je stereo optički mjerni sustav Aramis koji na temelju korelacijskog algoritma uspoređuje sliku zabilježenu u referentnoj konfiguraciji s nizom slika površine ispitnog uzorka u deformiranoj konfiguraciji. Primjenom predloženog mehaničkog i optičkog postava izračunati su pomaci i deformacije u promatranoj zoni interesa (tj. između dva V zareza).
Za svaki ispitni uzorak je izmjereno i analizirano polje smičnih deformacija, promjena debljine uzorka odnosno gužvanje materijala te polje pomaka u smjeru okomitom na promatranu površinu ispitnog uzorka. Povezivanjem podatka zabilježenih na jednoosnoj kidalici i izmjerenih polja pomaka i/ili deformacija metodom korelacije digitalne slike određen je dijagram ovisnosti smične deformacije i naprezanja. Osim toga, zabilježeni su dijagrami ovisnosti promjene debljine uzoraka o naprezanju u karakterističnim mjernim točkama.

Abstract (english)

Determining the mechanical properties of materials at simple and multiaxial loading is of great importance since most of the engineering structures are subjected to the complex loading regimes during their exploitation. The aim of the experimental investigation is to identify the mechanical parameters of the material in order to describe material response in a more reliable way and consequently evaluate the lifetime of the constructions. The existing experimental methods for mechanical investigation when the sample is subjected under shear loading have been constantly modified in the last few years because an additional out of plane bending effect was noted. The most known methods of mechanical shear testing are conducted on the Iosipescu and Arcan rigs. The latter test methods use butterfly specimen with two symmetrical V notches in order to achieve an uniform shear state. Furthermore, in order to access the material behaviour under shear loading regime can be achived by applying torsion to the circular or rectangular bars.
In this work, the experimental investigation was performed on butterfly samples. The mechanical tests have been conducted on the uniaxial Beta 50-5 testing machine (Messphysik Austria). The shear laoding was carried on the test sample via modified multiaxial Arcan rig. The aim of this thesis is to determine the out of plane displacements and strains occurring on the butterfly specimens with different thicknesses. For the proposed investigation, samples with 1, 2, 3 and 4 mm thicknesses were made of DC01 constructional steel. The displacement and strain fields were measured by digital image correlation method on the surface of the sample. A stereo optical measuring system Aramis was used to measure the out of plane displacements. The proposed comercial measuring system compares the image of the region of interest taken in the reference configuration with a series of images captured in the deformed configuration. Aramis measuring system is based on the correlation algorithm. The displacement and strain fields of the observed, between the two V notches, were calculated using the proposed mechanical and optical setup.
Shear strain field, change of thickness of the sample or (i.e. the material wrinkling ) and the displacement field in the perpendicular direction of the observed surface region were measured and analyzed for the four test samples. Shear stress and strain relation was determined coupling the data reported on the uniaxial testing machine and the measured displacement and strain fields is determined. Moreover, the relation of the change of thickness and shear stress are reported for the characteristic measuring points.

• Keywords: Arcan test metoda; leptirasti uzorak; gužvanje materijala; metoda korelacije digitalne slike; optički mjerni sustav Aramis.
• Keywords (english): Arcan Rig; Butterfly Specimen; Material Wrinkling; Digital Image Correlation Method; Aramis Optical Measuring System.
• Language: croatian
• URN:NBN: urn:nbn:hr:235:192032
• 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 00:34:34